ABB Review Special Report - ABB - ABB Group

Contents61319252932374247HVDC superhighways for ChinaNew HVDC transmission lines will carry electricity from theThree Gorges power plant to China’s coastal regions.FACTS: improving the performance of electrical gridsHow flexible AC transmission systems let utilities utilize theirexisting power lines more efficiently.ABB static var compensator stabilizes Namibian grid voltageNamibia’s long transmission lines give rise to unusual resonance.A new SVC has solved the problem.Advanced transformer control and monitoring with TECABB’s TrafoStar Electronic Control system models a transformer’sactual state, allowing condition-based maintenance.Power systems consultingA look at ABB power systems applications that integrate the domaincompetence of consulting experts with the latest software tools.Inform IT Wide Area MonitoringPSG modules from ABB optimize asset utilization and can preventthe collapse of entire power networks.Industrial IT and the utility industryHow does the unique business environment of the utility industrybenefit from Industrial IT?A battery energy storage system for AlaskaThe world’s largest BESS is providing essential back-up power for90,000 people in the Fairbanks area.High-voltage cable technologyNew XLPE cable system applications are available that can oftencompete with overhead lines.535761Powering Troll with HVDC Light TMNew ABB technologies allow power to be supplied from land toplatforms offshore.SwePol Link: new environmental standards for HVDC transmissionA unique HVDC link connects the electricity networks of Polandand Sweden.50 years of HVDC transmissionABB has supplied more than half of the world’s HVDC transmissioncapacity.2Special ReportABB Review

EditorialCity lights – a ‘power showcase’built on technology and experienceIn the aftermath of the recent poweroutages that plunged northeasternAmerica and parts of Europe into darkness,politicians and utility ownersrushed to debate the state of the world’spower infrastructure. The outcome ofthis discussion has been general agreementthat more investment is needed.But besides pointing out the vulnerabilityof outmoded infrastructure, theblackouts also served to make a point:wherever we live, we can no longerunquestioningly count upon a reliablesupply of electrical power.While these events gave a full-scaledemonstration of what can happenwhen unstable power systems are drivento their operational limits, it is goodto know that technologies are availablethat could almost certainly have preventedthem from happening.ABB is the world’s leading providerof power technology products andsystems. Constant investment in theirfurther development has enabled ourcompany to book several remarkableachievements in recent years.For example, the world’s largest batterysystem, which went into operation inAlaska in 2003, relies on ABB convertertechnology. Such systems bridge thetime between power cuts and the startupof emergency power generation.Alaska’s new battery is designed toprovide 40 MW of electrical power for15 minutes. Other battery installationsempowered by ABB converter technologyare soon to go into operation inthe United States.ABB is the undisputed world leader inHVDC transmission. The power convertersat the heart of this technologycan make a huge contribution to gridstability. An HVDC power transmissionlink between the Three Gorges damand Changzhou in China successfullycompleted all trials in 2003, and has thecapability to operate at power levels ofup to 3300 megawatts – a new worldrecord! In Brazil ABB recently commissionedpower transmission systems witha total length of 1267 kilometers. Constructionof the systems, which includedfive substations and four series compensationbanks, was completed in justtwelve months.The list goes on: the largest-ever gas-insulatedsubstation for an important nodein the Saudi Arabian high-voltage network;the world’s longest undergroundhigh-voltage cable, developed and installedby ABB, stretching 177 kilometersfrom Victoria to South Australiaand the winner of environmental andengineering awards.ABB also holds the world record in highpowerswitching with its generator breakers,which can interrupt up to 200 kA atgenerator voltage levels of around 30 kV.These records are solid proof of ABB’sability to provide world-class powertechnology, and of our company’sstrong commitment to research anddevelopment. Such performance isbased on R&D programs that investigatethe physical limits of current interruptionand high-voltage insulation, orthe application of semiconductorswitching in our power electronicsdevices.In addition to device-oriented R&D,ABB also looks at the ‘big picture’. Anexample is our wide area approach tomonitoring power system dynamics andnetwork stability. Engineering tools wehave developed enable us to analyze acomplete grid in a very short time, andpropose significant improvements.This Special Report is devoted to ABBtechnologies which, by ensuring networkstability, prevent the emergenceof situations that could cause entirepower systems to collapse. As anoverview of our company’s broad competencein this important area, the Reportdemonstrates ABB’s ability to supplythe utility industry with each andevery part of its infrastructure. To makesure that electrical energy, upon whichwe depend so much, is available whereverand whenever it is needed.H. Markus BayeganChief technology officerABB LtdSpecial ReportABB Review3

ForewordReliable grids, with power technologiesfrom the market leaderenced business leaders. ABB has builtits reputation in power technology onthese three strengths.The recent blackouts in the US andEurope have made more than just themedia think about the critical importanceof a secure and reliable supply ofpower. In our homes and throughoutbusiness and industry, the message isclear: no longer can we take for grantedthat power will simply be availableeverywhere, always.Reliable power grids are the result of apartnership between governments, theelectric utilities, consumers and, notleast, the providers of the all-importanttechnology that generates, transmitsand distributes the power so efficiently.Over a country’s power infrastructureflows its lifeblood – the energy that isessential to efficient running of ourhomes and offices, our factories andairports. Much of our future prosperitywill depend on how we look after it.Modern power systems are the result ofcontinuous development and improvementwhich, over the years, has led tohighly sophisticated and complex technologies.Their reliable operation is atribute to the work of dedicated scientists,innovative engineers and experi-Invention and innovation have a longtradition at ABB, and many of the keytechnologies upon which the powerindustry is founded were pioneered byour company. Our track record goesback more than a century, and includesthe world’s first three-phase powertransmission system and the world’s firstself-cooling transformer. ABB also pioneeredHVDC technology. To mark thisachievement, our company will celebrate‘50 years of HVDC’ together withour customers in spring 2004.It is this pioneering spirit that still drivesus today. Recent breakthroughs includeour HVDC Light TM technology, whichextends the economical power range ofhigh-voltage direct current transmissiondown to just a few megawatts andopens up new possibilities for improvingquality in power grids.Our utility and industrial customersaround the world rely on proven powertechnologies, researched, developedand made by ABB. In power transmissionand distribution, ABB is the recognizedleader, with a world market shareof some 20 percent.Every fourth power transformer andhigh-voltage circuit breaker in the worldcomes from ABB. Some of our high-endproducts and systems – generator breakers,for example – have beaten eventhis proud record and captured morethan half of the world market. The sameis true in other important areas of thepower sector, like high-voltage directcurrent (HVDC) transmission or flexible4Special ReportABB Review

Forewordalternating current transmission systems(FACTS).State-of-the-art technologies such asHVDC and FACTS have precisely thequalities and capability that arerequired to prevent blackouts.HVDC lets utilities solve two problemsat the same time: using it to interconnectasynchronous power grids notonly increases reliability, but also setsthe stage for power trading acrossthose grids. Most of the world’s powernetworks were designed as nationalgrids or as regional grids within acountry. To facilitate open markets,these networks increasingly requireHVDC interconnections.With FACTS, utilities have devices attheir disposal with which they can betterutilize their existing infrastructure.FACTS provide an alternative to the constructionof new transmission lines orpower generation facilities by helpingto maintain or improve the operatingmargins necessary for grid stability. As aresult, consumers get more power withoutany extra strain being put on theenvironment, and projects are completedin a substantially shorter time.Wide area monitoring (WAM) systems areanother ABB offering that can preventthe collapse of entire power networks.GPS-synchronized current, voltage andfrequency information gives power systemoperators a dynamic overview of thenetwork conditions, and indicates theonset of conditions that, if unchecked,could cause system instability.The power grids of the 21st centurymust incorporate such high-end technologiesif they are to meet all thechallenges that lie ahead. The blackoutsof 2003 have served notice on theutilities, and demonstrated to the widerpublic, that power grids are vulnerable.In many countries, deregulation has alltoo often undermined the will to makenecessary investments in high-endtechnologies.A first step toward correcting this situationwould be for regulators to offer investors,such as utilities and developers,special incentives that encourage themto install technologies which can beimplemented quickly and increase therobustness of their transmission grids.In addition, quality standards for thepower supply are needed to ensurepower reliability and security.ABB is ready to give its best: proventechnology. But beyond superior powerproducts, systems and services, there isanother decisive contribution that ABBcan make: speed. Short delivery times,guaranteed by a commitment to beingfastest in everything we do, are inkeeping with the prevailing sense ofurgency. Power consumers around theworld do not want to wait, and shouldnot have to wait, one moment longerfor a reliable power supply.Peter SmitsMember of the Executive CommitteeHead of Power Technologies DivisionABB LtdSpecial ReportABB Review5

HVDC superhighwaysfor ChinaLeif Englund, Mats Lagerkvist, Rebati DassWhen completed in 2009, the Three Gorges hydroelectric powerplant being built on the middle reaches of the Yangtze river will bethe largest of its kind anywhere in the world. With 26 turbinegenerators,each rated at 700 MW, the total generating capacity willbe a staggering 18.2 gigawatts.No less challenging was the development of a technically andeconomically viable transmission system to carry this power toChina’s coastal regions, where it is urgently needed. After carrying outfeasibility studies, the State Power Grid of China decided to build ahybrid AC-DC transmission system with over 10,000 km of HVAC andHVDC lines and about 2475 MVA of transformation capacity. The HVDCsystems leaving the power plant site include bipolar transmissionsuperhighways with ratings totaling more than 10,000 MW.6Special ReportABB Review

Two of the world’s most powerfuland longest high-voltage direct current(HVDC) power transmission highways,each with a nominal rating of3000 MW, are currently being installedin China. Being built by ABB in cooperationwith the State Power Grid ofChina, they will eventually carry cleanhydroelectric power from the ThreeGorges power plant, situated on themiddle reaches of the Yangtze river, tomajor load centers near Shanghai andShenzheng on the Chinese coast.1Location of the Three Gorges power plant on the Yangtze riverThree Gorges DamBeijingHigh availability and a low forced outagerate were key goals from the start ofthe transmission projects. Advancedtechnologies, backed up by solid fieldexperience and featuring built-in operationalflexibility and low maintenance,are therefore being used in all thecrucial areas.To promote and ensure the success ofthe projects at all stages, close cooperationamong ABB, the client, the client’sdesign and inspection representatives,and local equipment manufacturers,was enshrined in the project contractsin the form of training and transfer oftechnology (see panel).Three Gorges power plantThe Three Gorges dam across the Yangtzeriver 1 is the largest of its kind inthe world. Approximately 1.5 kilometerslong and 185 meters (590 feet) high, itsreservoir, with a normal water level of175 meters (560 feet), will stretch over560 kilometers (350 miles) upstream.The hydroelectric plant, with 26 turbine-generators rated at 700 MW, will havea total capacity of 18.2 gigawatts (thenext-largest hydropower plant, Itaipu inBrazil, has a capacity of 12 GW). It isplanned to later install a further six unitsin an underground powerhouse, takingthe total capacity to 22.4 GW. This figurerepresents a more than six percent increasein China’s current total installedcapacity of 350 GW. The average yearlyproduction of the Three Gorges plantwill be 84.7 TWh [1,2].ChongqingYangtzeYellow RiverThree Gorges-Changzhou HVDCHong KongShanghaiWuhanThree Gorges-ShanghaiHVDC (planned)Three Gorges-Guangdong HVDCPower evacuation systemThe power generated by the ThreeGorges plant will be transmitted to gridsin central China, east China, Sichuanand Guangdong via the Three GorgesTransmission System. With over 10,000kilometers of HVAC and HVDC lines,this system will form the basis fora new national transmission grid, as thepresent seven regional power networksand five independent provincial networkswill be combined to create twoTransfer of technology (ToT) and local manufacturingThe contracts for both projects (3GC and 3GG) included extensive co-design, training andToT programs.The co-design program calls for the detailed design to be carried out jointly by design engineersand experts representing SPG and ABB.Training of SPG’s representatives covers maintenance and operation. Its goal is to ensureproper operation and maintenance of the projects by local personnel.The ToT programs include know-how transfer in HVDC system design, control design andapparatus manufacturing to different organizations, ABB as well as non-ABB, in China. Theseprograms will serve China’s long-term objective of increased self-reliance in the design andproduction of high-tech HVDC equipment.Special ReportABB Review7

new regional networks. A national integratedgrid is planned for 2015.A major portion of the power will becarried to China’s industrialized coastalareas in Shanghai and Shenzheng bymeans of four HVDC links 2 :Gezhouba-Shanghai 1200-MW HVDCbipole, in operation since 1991.Three Gorges – Changzhou 3000-MWbipole (3GC), commissioned in May2003.Three Gorges – Guangdong 3000-MWbipole (3GG), currently being commissioned.Three Gorges – Shanghai, 3000 MW,scheduled to be operating by 2007.HVDC was chosen to transmit powerfrom the Three Gorges plant for severalreasons. Since the central and eastChina/Guangdong AC networks arenot synchronized an AC transmissionscheme would have required coordination,and it would have been verydifficult to ensure adequate stabilitymargins. HVDC allows controlled transmissionof power between the networks,which also retain their independence.DC is also more economic interms of construction costs and losses.Five series-compensated 500-kV AClines would be necessary to transmitthe same amount of power, and eachline would require a larger right-of-waythan one HVDC transmission line for3000 MW.Unmatched experience withHVDC bulk powerABB’s record of large bipolar HVDC installationsis unmatched. Prior to winningthe ThreeGorges contract,ABB had successfullybuilt a wholeseries of largebipolar installationsworldwide,for example:Itaipu (Brazil):two bipoles,each rated 3150 MWIntermountain Power Project (USA):one bipole, 1920 MWRihand-Dadri Project (India): onebipole, 1500 MWHVDC allows controlledtransmission of powerbetween the central andeast China/GuangdongAC networks, whichremain independent.2Left bank14x700 MWThree Gorges12x700 MWRight bankFour HVDC links will carry hydroelectricity from the Three Gorges power plantto China’s coastal area and the industrial region of GuandongCentral ChinaChandrapur–Padghe Project (India):one bipole, 1500 MWQuebec-New England Multiterminal(Canada/USA): three bipolar stationsrated 2250/2250/2000 MWHighway construction onscheduleABB was awarded the first contract, tosupply equipment for two converterstations for the 3000-MW HVDC bipolarlink between Three Gorges and eastChina, in April 1999. This entrusted ABBwith overall project responsibility, includingthe supervision of site work undertakenby the client. The contract alsoincluded ToT, covering HVDC systemdesign, control design and equipmentmanufacturing. Approximately 85% ofthe total contractvalue was forequipment or servicesprovided bythe ABB Group.The installationwas commissionedon time inMay 2003.In October 2001 ABB won a second order,this time for the 3000-MW HVDClink between Three Gorges and Guangdongprovince. This fast-track projectcuts 30 percent off the normal lead-±500 kV, 3000 MWThree Gorges – Changzhou±500 kV, 1200 MWGezouba – Shanghai± 500 kV, 3000 MWThree Gorges – Shanghai±500 kV, 3000 MWThree Gorges – Guangdongtime, enabling the first pole to be commissioned28 months after signing ofthe contract. Similar in scope to the3GC, it provides for more local content.3East ChinaGuangdongIndoor DC yard at Zhengpingconverter station (3GC)8Special ReportABB Review

The ToT covers HVDC system design aswell as the design of the control andprotection system. This project is welladvanced and on schedule.4500-kV yard with SF 6 gas-insulated switchgear, at Jingzhou converter station (3GG)3GG benefits from 3GCThe 3GC project has established a worldrecord by transmitting 1650 MW on asingle pole. Since the Zhengping converterstation is exposed to very heavyindustrial pollution, the DC pole insulatorshad to be longer than those themanufacturers could provide. This andthe difficulty of coordinating the externaland internal insulation of extra-longbushings led to the decision to build indoorDC switchyards 3 . All high-potentialDC equipment is installed indoorsand all the DC neutral equipment is outdoors.There are four separate halls foreach pole: one for switches, two for theDC filter capacitor banks, and one forthe DC PLC capacitor bank.The 3GG project is in a class of its ownwith regard to the very short 28 monthsto commissioning for monopolar and32 months for bipolar operation. Herethe knowledge and experience baseprovided by the 3GC project proved tobe a huge asset. Areas that profited includedthe project engineering phaseand the equipment design and deliverytimes, all of which could be significantlyreduced. The cost benefit to theclient was also considerable.5Converter stationLongquan (3GC)Jingzhou (3GG)To keep the AC yard of the 3GG Jingzhouconverter station as small as possible,outdoor gas-insulated switchgear (GIS) isused for all of the ten 500-kV bays 4 .Power circuit arrangement used for the 3GC and 3GG projectsy0y0y0y0yy3000 MW+500 kVDC-lineElectrodelineDC-line–500 kVyyy0y0y0y0Converter stationZhengping (3GC)Huizhou (3GG)The transmission systemsThe 3GC and 3GG projects are bothbipolar transmission schemes [3] withidentical main primary and secondaryequipment and operating strategies.The two 3GC converter stations are atLongquan (Hubei province) and Zhengping(in Changzhou, Jiangsu province),about 890 km apart. Longquan converterstation is situated some 50 km fromthe Three Gorges Dam. The receivingstation at Zhengping is approximately200 km from Shanghai. Power will betransmitted eastward during the peakgeneration period and toward the centralpower grid whenever reservoirwater needs to be conserved.The converter station at the transmittingend of the 3GG project is located 16 kmfrom Jingzhou city, about 135 km fromthe Three Gorges power plant. The receivingstation is at Huizhou, in Guangdongprovince. Power will be transmittedover a distance of 940 km.Special ReportABB Review9

Power ratingsThe links are designed for a normal ratingof 2 x 1500 MW under the (relativelyconservative) specified conditions.They have been designed for a continuousoverload capability of 3480 MW,and a 5-second overload capability of4500 MW.6Thyristor valve structuresTo minimize bipole outage the HVDCsystem can be operated with balancedbipolar currents, using the ground matsof the converter stations as temporarygrounding, should the ground electrodesor their lines be out of service.The nominal reverse power transfercapability is 90% of the rated power.The HVDC links are designed to operatecontinuously down to 70% of the ratedDC voltage. The main technical dataare given in the table.Power circuit arrangementThe main circuit arrangement of thetwo links 5 is identical except for thereactive power compensation equip-Main parameters3GC (3GG)Nominal power rating, MW 3000Nominal dc voltage, kV ±500Transmission distance, km 890 (940)Power overloads at maxambient temperatures withredundant cooling inservice, MW:Continuous 31502 hour 339010 seconds 42305 seconds 4500Converter transformers:Type1-phase,2-windingPower rating, MVA 297.5/283.7Smoothing reactors:TypeOil-insulatedValue, mH 290/270 (290)Thyristor typeYST-90DC filter typePassiveAC filter typePassiveAC system voltage, kV 525/500AC system frequency, Hz 50ment. Stable steady-state and dynamicoperation of the AC-DC systems is ensuredby optimizing use of the reactivepower capacity of the generators in theThree Gorges power plant and the ACnetworks at each end of the links. Oneand-a-halfbreaker configurations areused on the AC side at both stations.The links have beendesigned for a rating of2x1500 MW, a continuousoverload capabilityof 3480 MW, anda 5-second overloadcapability of 4500 MW.In addition to the bipolar transmissionscheme, the links can be connected formonopolar transmission with either aground or metallic return. The maincircuit connection on the DC side istypical for an HVDC bipole with over-head transmission line. Metallic returntransfer breakers and ground returntransfer switches have been installed tomeet the requirements of monopolarmetallic return operation, and providecapability for uninterrupted transfer.Neutral bus grounding switches arealso installed at the neutral buses ofboth stations to meet temporarygrounding requirements.Thyristor valvesA double valve scheme 6 was chosento take account of the converter transformersbeing single-phase, two-windingunits. Longquan and Jingzhou converterstations have 90 thyristors (3 kA,7.2 kV) per valve, while at the receivingstations Zhengping and Huizhou eachvalve has 84 thyristors (same rating).Dry-type damping capacitors and filmDC resistors are used. Comprehensivefire detection and protection is incorporatedin the valve hall design.AC filteringFour types of filter are used: doubletuned 11th and 13th, double tuned 24th10Special ReportABB Review

and 36th, double tuned 12th and 24th,and C-type 3rd harmonic. Shunt capacitorbanks, with and without dampingreactors, balance the reactive powerrequirement at Jingzhou, Zhengping andHuizhou converter stations.DC filteringRobust passive DC filtering ensures aperformance level of 500 mAp (bipole)/1000mAp (monopole) for bothprojects. Each terminal pole has twofilter arms designed as double tunedfilters, one tuned to the 12th and 24thharmonics and the other to the 12thand 36th harmonics.7Control and protectionThe projects’ control and protectionstrategies are realized with ABB’s stateof-the-artMACH2 system. MACH2features highlevelperformance,lowmaintenance, avery powerfulprogrammingenvironmentand good integrationwithSCADA systems.The SCADAsystems enable information about theoperating status of each converterstation to be accessed remotely by dispatchcenters. These centers have fullremote control capability and can regulatepowertransmissionPower will be transmittedeastward during the peakgeneration period and towardthe central power grid wheneverreservoir water needsto be conserved.Converter transformer arrangement per poleon the link.Terminal-toterminalcommunicationisvia opticalfiber groundwire. Capacitynot neededfor communicationis used for dispatch and for datatransfer on the networks, but could alsobe used for commercial purposes.Control functions such as power ramping,frequency control and dampingmodulation, are also integrated. Thestation engineer can adjust the interfaceand parameters as required bythe system.Converter transformers andsmoothing reactorsThe single-phase converter transformers7 in the Longquan and Jingzhou stationsare rated 297.5 MVA, 525/√3:210.4/√3(210.4 for Y-D) kV, 16% reactance, withan OLTC tap range of +25/-5 (1.25%per step). The Zhengping transformersare rated 283.7 MVA, 500/√3:200.4/√3(200.4 for Y-D) kV, 16% reactance.Here, the OLTC tap range is +26/-2. Inthe Huizhou station the transformersare rated 283.7 MVA, 525/√3:200.6/√3(200.6 for Y-D) kV, 16% reactance, alsowith an OLTC tap range of +28/–4(1.193% per step). Dry-type bushingsare used for the valve hall penetration.The converter transformers at Longquan,Jingzhou and Huizhou are alsoequipped with electronic control,allowing analysis and reporting, plusintelligent fan control to minimizelosses.The smoothing reactors are connectedto the valves via the bushing penetratingthe valve hall wall. An electroniccontrol system for the reactors atLongquan, Jingzhou and Huizhoufeatures the same capability as thatprovided for the transformers.Special ReportABB Review11

Power take-offElectric power generation in China tends to be located in the northeast (coal-fired), and in thewest and southwest (hydropower), while the main consumer areas are in the eastern coastalarea and southern industrial region of Guangdong.China’s total generating capacity of more than 350,000 MW (end of 2002) needs to grow to atleast 500,000 MW by the end of the decade to cope with increased demand. Due to its fastgrowingeconomy, many areas, including Shanghai, Guangdong and Zhejiang provinces, arealready today suffering from a significant power supply shortfall. Guangdong province, for example,has a deficit of over 30,000 MW, some of which is met through imports from neighboringHong Kong.China now plans to start adding 25,000 to 30,000 MW each year through 2005, for an annualgrowth of 7% to 8%. Both AC and DC transmission are foreseen for the extensions. Over the nextten years, the HVDC market – long-distance transmissions and back-to-back stations to interconnectthe regional networks – is estimated at 40,000 MW.DC-side breakers and switchesSF 6 breakers are used for all the highspeedDC switches: metallic returntransfer breakers, neutral bus groundingswitches, neutral bus switches andground return transfer switches. Theground return transfer switch is theonly one of these to be of conventionalpassive design. All the others have anactive auxiliary transfer circuit consist-ing of a capacitor and a charger. Thecharger gives the DC switches extracurrent commutation capability, enablingthem to handle even the highestoverload currents.Operating configurationsThe links can be operated in many differentconfigurations and modes. Emergencyoperation is provided for, as is“A remarkable achievement in the history of ABB’s HVDC technology”The inauguration of the Three Gorges – Changzhou HVDC link in August 2003 in the presenceof representatives of the Chinese government, State Council Three Gorges Office, State PowerGrid Corporation and ABB, marked the successful completion of trials and the start-up of commercialoperation. The 500-kV, 890-kilometer long HVDC link can operate at world record levelsof up to 3,480 megawatts, and when the Three Gorges generators begin operating later thisyear it will transmit electricity to millions of consumers in eastern China. The largest and longestbipole DC power transmission link in China was completed on schedule in four years.“Considering the project’s technical complexity, this is a remarkable achievement in the historyof ABB’s HVDC technology,” says Peter Smits, head of ABB’s Power Technologies division.“By delivering this challenging project on time almost to the day, we have demonstrated ourcommitment to speed and precision, and to improving the quality of life for millions of Chinesecitizens.”operation without telecommunication.Through accurate measurement andcontrol it is ensured that in the case ofbipolar balanced operation with localstation ground the unbalance current toground will be zero.The operating modes are:BipolarMonopolar earth return and metallicreturnReduced DC voltage (from 500 kV to350 kV)Reverse power operationBipole and pole power controlPole synchronous and emergency(separate) power controlPole backup synchronous control(for modulation of DC current withoutinter-station telecommunication)Pole current controlMeeting China’s energy demandChina plans to substantially expand itsgenerating capacity by 2010 in order tocope with the predicted growth indemand (see panel). At the same time,two new regional networks will becreated as the basis for a new nationaltransmission grid. HVDC, with all itsadvantages for long-distance transmission,is expected to play a major rolein the extensions.Leif EnglundMats LagerkvistRebati DassABB Power TechnologiesSE-771 80 LudvikaSwedenleif.englund@se.abb.commats.lagerkvist@se.abb.comrebati.dass@se.abb.comReferences[1] Introduction to China’s Yangtze River Three Gorges Project. The PRC State Council Three Gorges Construction Committee, Ministry of Land andResources, State Environmental Pollution Administration, State Bureau of Cultural Relics, September, 2002.[2] Z. Xiaoqian, D. Gongyang, G. Ricai: The Three Gorges power grid and its development. Cigré 1998, 37–203, Paris.[3] Z. Xiaoqian, et al: Design Features of the Three Gorges – Changzhou ±500 kV HVDC Project. Cigré 2000, 14–206, Paris.12Special ReportABB Review

FACTSImproving the performanceof electrical gridsRolf Grünbaum, Åke Petersson, Björn ThorvaldssonAfter years of underinvestment in their transmission infrastructure, power utilities are being forced tolook at ways of utilizing their existing transmission lines more efficiently, at possibilities for cross-bordercooperation, and at the issue of power quality. This situation has dramatically increased interest in newas well as traditional solutions.FACTS (Flexible AC Transmission Systems), such as SVC, SVC Light ® , TCSC and others, are just suchsolutions. They take advantage of the considerable technical progress made in the last decade andrepresent the latest state of the art. While a typical application would be to increase the capacity of anygiven transmission line, this article describes some special cases with unique requirements and howthey were met.If prestigious projects were ever neededto demonstrate FACTS’ credentialsas an improver of T&D performance,none could serve better than the Dafang500-kV series capacitors helping to safeguardBeijing’s power supply, the EaglePass back-to-back tie straddling theUS/Mexican border, or the ChannelTunnel rail link. These, in their differentways, show why FACTS is arousing somuch interest in the electrical supplyindustry today.Dafang: series capacitors safeguardthe Beijing area power supplyPower demand in the area served by theNorth China Power Network, with 140million people and including Beijing, isgrowing at a steady pace. Installing newgeneration plant and transmission lines isnearly impossible due to urban growth.An attractive alternative is to insert seriescapacitors in the existing transmissioncorridor to provide series compensation.Special ReportABB Review13

1The Dafang 500-kV series capacitorsThe main protective devices used areZnO varistors and circuit-breakers. Thefirst is to limit the voltage across thecapacitor and is supplemented by aforced-triggered spark gap to handleexcess current during a fault sequence.The circuit-breakers connect and disconnectthe series capacitors as required.They are also needed to extinguishthe spark gap, as it is not selfextinguishing.The capacitors are rated for operationduring normal, steady-state grid conditionsas well as for severe system contingencies,such as loss of one of thetwo parallel 500-kV lines. In such acase, the capacitor of the line remainingin service must be able to take the fullload of both lines for a certain amountof time. This was, in fact, one of thereasons for installing the series capacitorsin the first place – to ensure thesafe transfer of power to the Beijingarea even with a line down.ABB was contracted to do this, and installedtwo series capacitors (each rated372 MVAr, 500 kV) in the middle of eachline of a 300-km twin-circuit corridorbetween Datong and Fangshan 1 . Theycame on stream in June, 2001, a merenine months after the contract wasawarded and some 3 to 6 months fasterthan for similar installations.A series capacitor acts to reduce thetransfer reactance of the power line atpower frequency (50 Hz) and suppliesreactive power to the circuit at the sametime. The benefits of this are:Increased angular stability. Theremust always be a certain differencebetween the voltage phase angles ateither end of the power line to enabletransmission. The phase angledifference increases with powertransmission and the series capacitorkeeps the angular difference withinsafe limits, ie it ensures that the angulardifference does not increase somuch that it could jeopardize theangular stability.Improved voltage stability of thecorridor.Optimized power sharing betweenparallel circuits. Without series capacitors,the line with the least powertransmission capacity would saturatefirst and no additional power couldbe fed into the system, despite thefact that the other line still has capacityto spare. The series capacitorsredistribute power between the linesfor better overall utilization of thesystem.The series capacitors are fully integratedin the power system and benefit fromits control, protection and supervisorycapability. They are fully insulated toground.Eagle Pass Back-to-Back (BtB) LightSVC Light technology 1) has successfullysolved power quality problems in severalprojects undertaken by ABB. Basedon a common platform of voltagesource converters (VSC), SVC Light alsoprovides solutions for power conditioningapplications in transmission systems.The Eagle Pass tie is a good exampleof a project in which the VSC platformis configured as back-to-back HVDC,although functionally with priority givento voltage support with the dual SVCLight systems.Most important in this respect is the factthat installation of active power transfercapability, using HVDC Light across acertain distance or in a back-to-backconfiguration, will provide both bidirectionalactive power and dynamic reactivepower support simultaneously.Thus, strong voltage support is readilyavailable along with the steady-statepower transfer.The Eagle Pass substation (operated byAmerican Electric Power, AEP) is locatedin a remote part of Texas, on theMexican border, and is connected to theTexas transmission system through two138-kV transmission lines. The nearestsignificant generating station is located1) SVC Light is a product name for an IGBTbasedstatic synchronous compensator fromABB.14Special ReportABB Review

145 km away and provides very littlevoltage support to the Eagle Pass area.Eagle Pass also has a 138-kV transmissionline that ties into Piedras Negrassubstation (operated by CommissionFederal Electricas, CFE) on the Mexicanside. This is used mainly in emergenciesto transfer load between power systems,but such transfers involve interruptingthe power as the CFE and AEP systemsare asynchronous (despite both being60 Hz). To overcome this disadvantage,and also solve problems arising fromincreasing demand, a better solutionwas sought.ABB’s response:voltage source convertersLoad flow studies demonstrated that theinstallation of a 36-MVAr voltage sourceconverter directly at the Eagle Pass substationwould provide years of respite.Installation of a VSC is ideal for weaksystems as the alternative, reactivesupport provided by shunt capacitors,decreases rapidly when the voltage isreduced. Extending the scenario, twoVSCs connected back-to-back wouldnot only supply the necessary reactivepower but also allow active powertransfer between the two power systems.A BtB scheme would enable the138-kV line between Eagle Pass andPiedras Negras to be continuously energizedand allow the instantaneous transferof active power from either system.2EaglePassAs commutation is driven by its internalcircuits, a VSC does not rely on the connectedAC system for its operation. Fullcontrol flexibility is achieved by usingpulse width modulation (PWM) to controlthe IGBT-based bridges. Furthermore,PWM provides unrestricted controlof both positive- and negative-sequencevoltages. Such control ensures reliableoperation of the BtB tie even when theconnected AC systems are unbalanced.In addition, the tie can energize, supplyand support an isolated load. In the caseof Eagle Pass, this allowed the uninterruptedsupply of power to local loadseven if connections to one of the surroundingnetworks were tripped. Bothsides of the tie can also be energizedfrom ‘across the border’, without anyswitching that could involve interruptionsof supply to consumers.The back-to-back installationA simplified one-line diagram of the BtBtie in Eagle Pass is shown in 2 .3VSCSingle-line diagram of back-tobacktie at Eagle PassVSCPiedrasNegrasThe BtB scheme consists of two36-MVA VSCs coupled to a common DCcapacitor bus. The VSCs are of the NPC(neutral point clamped) type, alsoknown as three-level converters. EachVSC is connected to a three-phase setof phase reactors, each connected toa conventional step-up transformeron its respective side of the BtB. Thelayout of the BtB installation is shownin 3 .BtB operating modesThe two VSCs of the BtB can be configuredfor a wide range of differentfunctions. At Eagle Pass, the main BtBoperating configurations are as follows:Voltage controlActive power controlIndependent operation of the twoVSCsContingency operation of the BtBVoltage controlIn this mode, both the AEP and CFEsystems are capable of independentvoltage control. The BtB provides therequired reactive power support onboth sides to maintain a pre-set voltage.Active power can be transferred fromEagle Pass back-to-back tieForeground: 138-kV equipment and harmonic filters. Middle: buildings with converters,controls and auxiliaries. Back: cooling towers for water-cooled IGBT convertersHaving the capability to control dynamicallyand simultaneously both activeand reactive power is unprecedentedfor BtB interconnections. This feature isan inherent characteristic of the VSC.Special ReportABB Review15

41.51.00.50-0.5-1.0-1.55002500-250-5001.51.00.50-0.5-1.0-1.51.51.00.50-0.5-1.0-1.540200-20-401.41.21.00.81.00.50-0.5Eagle Pass back-to-back tie: remote fault caseeither side while a constant system voltageis maintained on both. Any activepower transfers that are scheduled areautomatically and instantaneously lowered,if required, by the control systemPCIA 20000913 17;10;19 Uac Primary Sys APCIC 20000913 17;10;19 Iac P1 CPCIA 20000913 17;10;19 Iac Sys APCIA 20000913 17;10;19 Uac Sys APCIC 20000913 17;10;19 Uac S1 CPCIA 20000913 17;10;19 Udc Sys APCIA 20000913 17;10;19 PQ Ref Sys A-1.00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.01 AEP 138-kV voltages2 AEP step-down transformer secondarycurrents, in amps3 AEP phase reactor currents4 AEP 17.9-kV voltagesABCABCABCABCABCU+U-PQ5 AEP 17.9-kV phase-to-ground voltages,in kV6 DC voltages7 AEP converter, active (P) and reactivepower (Q) referenceto supply the reactive power needed tomaintain a constant voltage.1234567Active power controlIn this mode, active power can be transferredbetween the AEP and CFE systems.Power transfer is allowed whenthe voltage is within a dead-band. If thevoltage lies outside it, the BtB automaticallyreverts to voltage control mode.The active power flow is then automaticallyand instantaneously lowered bythe BtB to provide the required reactivepower support. The dead-band is designedso that local capacitor switchingor changes in remote generation thatcause slight voltage swings do not causethe BtB to switch to the voltage controlmode.Independent operation of the two VSCsShould maintenance be required on oneside of the BtB, the other side is stillable to provide voltage control to eitherside of the tie. This is done by openingthe DC bus, splitting it into two halves.As the DC link is open, no active powercan be transferred between the twosides of the BtB. Each VSC will then becapable of providing up to ±36 MVAr ofreactive support to either side.Contingency operation of the BtBIf one of the 138-kV lines into the EaglePass substation is lost, the remaining138-kV line can only support 50 MW ofload at the substation. Should this occur,the voltage falls below 0.98 pu and theBtB switches to the voltage controlmode. Active power is reduced automaticallyand instantaneously to makesure the 50-MW load level at the substation(AEP load plus the export to CFE)is not violated. The BtB supplies therequired reactive support to maintain a1-pu voltage. Load flow studies haveshown that the transmission line contingencyon the AEP side will have littleimpact on the power transfers from AEPto CFE.Dynamic performanceThe recording reproduced in 4 illustrateswell the highly dynamic performanceof the BtB Light installation atEagle Pass. Plots 1–7 show how the BtBresponded to lightning conditions in aremote area that caused a voltage dipin the AEP network. During the fault,the BtB current (capacitive) was increasedto almost 1 pu to support thebus voltage at Eagle Pass.16Special ReportABB Review

Channel Tunnel rail linkWhen the high-speed electrified railwayline between London and the ChannelTunnel to France is finished in 2007 itwill be possible to travel between Londonand Paris in just over two hours,at a maximum speed of 300 km/h. Therailway power system is designed forpower ratings in the range of 10 MWand which fluctuate (rapid accelerationand retardation). The traction feedingsystem that was supplied by ABB is amodern 50-Hz, 2 ž 25-kV supply incorporatingan autotransformer scheme tokeep the voltage drop along the tractionlines low. Power step-down from thegrid is direct, via transformers connectedbetween two phases 5 .5Power feeding system for the Channel Tunnel rail link between Englandand France. Singlewell substation with two single-phase static var compensators,each rated 25 kV, –5/+40 MVAr25 kV 25 kV 45 MVAr 40 MVArTCR 3rd 5th 7thTCR3rd5th7thSVCCatenaryFeeder400 kVSVCs for the three traction feedingpointsA major feature of this power system isthe static VAr compensator (SVC) support,the primary purpose of which is tobalance the unsymmetrical load and tosupport the railway voltage in the caseof a feeder station trip – when two sectionshave to be fed from one station.The second purpose of the SVCs is toensure a low tariff for the active powerby maintaining unity power factor duringnormal operation.Thirdly, the SVCs mitigate harmonicpollution by filtering out the harmonicsfrom the traction load. This is importantas strict limits apply to the traction system’scontribution to the harmonic levelat the supergrid connection points.The SVCs for voltage support only areconnected on the traction side of the interconnectingpower transformers. The45 MVAr 40 MVArsupergrid transformers for the tractionsupply have two series-connected medium-voltagewindings, each with its midpointgrounded. This results in twovoltages, 180 degrees apart, betweenthe winding terminals and ground. TheSVCs are connected across these windings;consequently, there are identicalsingle-phase SVCs connected feeder toground and catenary to ground.The traction load of up to 120 MW isconnected between two phases. Withoutcompensation, this would result inan approximately 2 % negative phasesequence voltage. To counteract theunbalanced load, a load balancer (anasymmetrically controlled SVC) hasbeen installed in the Sellindge substation.This has a three-phase connectionto the grid.The load balancer transfers active powerbetween the phases in order to createa balanced load (as seen by the supergrid).A brief explanation of how theload balancing works is given in thefollowing.Load currentWhen the load is connected betweentwo phases (B & C) only, the tractioncurrent can be expressed by two phasevectors, one representing the positivesequence and the other the negativesequence 6 . The summation of the twovectors is the resulting current (currentin phase A is zero and currents in phaseB and C are of equal magnitude, but ofopposite phase). Note that the vectoramplitudes are not truly representative.To compensate the negative sequenceand thus balance the current to be gen-6 Phase-sequence components of the load current7 Load current balancingIcIcIcIcIbIcIbIa+ Ia I=LOADI LOAD IaIa+ =I +LOAD I -LOAD ILBILB +I LOADIbIbIbIcIbSpecial ReportABB Review17

8400 kVCircuit of dynamic load balancer in Sellindge substation (33 kV, –80/+170 MVAr)25 kV 25 kV84 MVAr2x42 MVArCatenaryFeedererated by the power systems, the loadbalancer generates a (pure) negativephasesequence current, (I LB ), as shownin 7 . This current balances exactly thenegative-phase sequence current fromthe load (I -LOAD in 6 ).The load balancer in the Sellindge substation8 is optimized to handle a loadconnected between the C and A phases.Load balancing theory says that, tobalance a purely active load, a capacitorhas to be connected between phasesA and B and a reactor betweenphases B and C. The traction load alsohas a reactive part, which likewise hasto be balanced. In this substation, notonly the asymmetry is compensated butalso the power factor. This is achievedby inserting a capacitor between phasesC and A.RedundancyHigh availability is required, so all criticalcomponents are redundant: A completefourth redundant phase has beenadded in the main circuit. All the phasesneed to be as independent of eachother as possible.3rd5th7thTCRTCRStandbyphase33 kVlogic circuits, measuring transformers,relay protection devices and coolingsystem. Each of the connections to thesubstation busbars has a circuit-breakerand disconnector inserted in it. Filterscan be connected to or disconnectedfrom the fourth interphase to turn itinto either an inductive or a capacitivebranch.Two independent control systems acton the three-phase system, while thethyristor firing and logic circuits actdirectly on each interphase. The controlsystems are strictly segregated, asare the valve-firing logic circuits andthe overall protection system. If aninterphase fails, the control systemtrips it and automatically substitutesthe standby unit.The thyristor valves make use of a newtype of thyristor – a bidirectional devicewith two antiparallel thyristors on acommon silicon wafer. This halves thenumber of units needed in the valves.The thyristor is a 5-inch device with acurrent-handling capability of about2000 A(rms).The Dafang project is a classic exampleof a transmission capacity upgrade providingmuch-needed power to a fastgrowingarea, in this case the regionaround Beijing. The project was completedin the extremely short timeof nine months and brings existing,remotely generated power to an areawhere it is urgently needed.The case of Eagle Pass shows the possibilitiesoffered by new technologiesable to combine advanced FACTS propertieswith network interconnectioncapability. The latest developments insemiconductor and control technologyhave made this possible. Thanks to thisback-to-back tie, existing transmissionfacilities can be utilized to a muchgreater extent than before.Finally, the Channel Tunnel rail linkillustrates well the flexibility of FACTSdevices by showing how they can alsobe used to solve the problems createdby new, sophisticated types of load.The unbalance caused by new tractionloads, for example, can be mitigated,and downgrading of the electricity supplyfor other users avoided, by meansof the described solid-state solutions.These examples show that FACTS deviceswill be used on a much widerscale in the future as grid performancebecomes an even more important factor.Having better grid controllability willallow utilities to reduce investment inthe transmission lines themselves. ABBis currently exploring ways in whichFACTS devices can be combined withreal-time information and informationtechnologies in order to move themeven closer to their physical limits.These requirements have resulted ina unique plant layout and design forthe control and protection. There arefour fully independent ‘interphases’(an assembly of components connectedbetween two phases). Each interphasefeatures an independent set of filters,reactors, thyristor valves, thyristor firingSummary and outlookThe importance of improving grid performanceis growing for economical aswell as environmental reasons. FACTSdevices have established themselvesas the most suitable solutions for increasingpower transmission capabilityand stability.Rolf GrünbaumÅke PeterssonBjörn ThorvaldssonABB Power TechnologiesSE-721 64 VästeråsSwedenrolf.grunbaum@se.abb.com18Special ReportABB Review

PowerABB static var compensator stabilizes Namibian grid voltagefactor!Rolf Grünbaum, Mikael Halonen, Staffan RudinThe spectacular dune landscapes of Namibia are a key factor in the country’s booming touristindustry and a valuable source of revenue for the nation. Another, even more important pillar ofthe Namibian economy is the power-hungry mining industry. To cope with growing energy demandin these two sectors and to ensure a reliable power supply for the country as a whole, NamPower,Namibia’s national electricity utility, has installed a new 400-kV AC transmission system linking itsgrid system with the Eskom grid in South Africa. Voltage stability problems, which the new linewould have aggravated, have been resolved by installing a static var compensator from ABB.Special ReportABB Review19

While construction of the new linehas brought reliable power toNamibia, it was not without problems ofits own. The line’s length of 890 km, forinstance, aggravated certain problems –mainly voltage instability and near50-Hz resonance – that already existedin the NamPower system.1Auas static var compensatorAn ABB static var compensator (SVC) ratedfrom 250 MVAr inductive to 80 MVArcapacitive has been installed to solvethese problems. The turnkey project wasconcluded with the successful commissioningof the SVC in NamPower’s Auas400-kV substation 1 , just 18 monthsafter the contract was signed.The case for a new 400-kV gridPower consumption in Namibia is concentratedin Windhoek and in the northernregion, where most of the miningand mineral industry is located. Until recently,the NamPower grid consisted of aradial network, with bulk power suppliedby the Ruacana hydro-station in the northvia a 520-km 330-kV transmission circuit,linked by an 1000-km 220-kV interconnectionto Eskom’s system in the south.This network was often loaded to itsstability limits during low-load periodswhen Ruacana was not providingpower. The system is also unique forits long 220-kV and 330-kV lines andthe fact that the loads are small incomparison with the generationsources – two features that furtheraggravated the stability problems inlow-load conditions.To solve these problems, the utility decidedto build a 400-kV grid. The finalphase of construction – a 400-kV interconnectionbetween Auas and Kokerboom2 – was completed in 2000. Thissingle-circuit 400-kV AC transmissionline strengthens the NamPower systemby connecting it to Eskom’s system in2NamPower network3System impedance/frequency characteristics (a) and system near 50-Hz resonance (b)1000100080018005Ohms6004002Ohms600400612000340 100 200f (Hz)20000 50 100f (Hz)2ab1, 2 Existing system, with four and no generators3, 4 New system, with four and no generators5, 6 During 400-kV energization, with four and no generators20Special ReportABB Review

the south. However, with a length of890 km it is also very long, in fact oneof the longest lines of its kind in theworld. This and the network’s tree-likeconfiguration, coupled with remote generationand the very long radial linesoperated at high voltage, results in thecharging capacitance being high. Theeffect of this is to shift the existing parallelresonance closer to 50 Hz, makingthe network more voltage-sensitiveduring system transients, for examplewhen the 400-kV line is energized orduring recovery after a line fault clearance.Each of these phenomena manifestsitself as an extremely high andsustained overvoltage.Resonance and overvoltagesThe NamPower network has a first naturalparallel resonance frequency wellbelow 100 Hz, namely in the 55–70 Hzrange (curves 1 and 2 in 3 ).The effect of adding the new 400-kVline section (Aries-Kokerboom-Auas)and its four 100-MVAr shunt terminalreactors has been to shift the system’sfirst resonance into the 60–75 Hz frequencyrange (curves 3 and 4). (Thereduction in system impedance at50 Hz is due to the new 400-kV line,and an indication of how the systemhas been strengthened.)Curves 5 and 6 in 3 show the networkimpedance as seen at the Auas 400-kVbus the instant the 400-kV line is energizedfrom the northern section (fromthe Auas side) and before the circuitbreakeron the Kokerboom side isclosed.The impact of the resonance problemin the NamPower system is best illustratedby simulating the condition atAuas substation, represented by curve6. The voltage situation is shown in 4 ,in which the line circuit-breaker atAuas is closed at time t = 1.0 s and itis assumed that the breaker at Kokerboomis synchronized at t = 1.2 s. Dueto the large charging capacitance of theline the voltage first dips, then overshoots.The extremely high overvoltages appearingat Auas, with a peak value inexcess of 1.7 pu and a sustained transientovervoltage (TOV) of more than1.5 pu, attest to the severity of the problem.It is clear that as soon as 50-Hzresonance is triggered very high dynamicovervoltages appear with large timeconstants under certain system load andgeneration conditions.5400 kV Auas substation15 kVSingle-line diagram of the AuasSVCX400 kV/15kVSVC transformerTCR1 TCR2 TCR3 TCR4 Filter1 Filter2(spare)Auxsupply80 MVAr capacitive) and is installedprimarily to control the system voltage,in particular the extreme (up to 1.7 pu)overvoltages expected as a result of thenear 50-Hz resonance. An uncommonfeature of the project is that the SVC isinstalled in a system with very longlines, little local generation and faultlevels lower than 300 MVA.V (kv)46004002000-200-400-600Energization of the Auas-Kokerboom400-kV line from thenorthern section, without the SVC0.95 1.00 1.05 1.10 1.15 1.20 1.25t (s)The blue, green and red curves represent thedifferent phases (instantaneous values).Preliminary studies indicated that overvoltageswould appear that would makethe Nam-Powersystem inoperableunlessvery fast,effectiveand reliablecountermeasures are taken. Several solutionswere considered as an answer tothe resonance problem, including fixedand switched reactors, before deciding toinstall a FACTS device in the Auas substation.Preference was given to conventional,proven SVC technology [1].SVC design featuresThe Auas SVC has a dynamic rangeof 330 MVAr (250 MVAr inductive toThe SVC that is installed is of a newtype, developed by ABB for power applications.Studies showed that overvoltagescould make the NamPower systeminoperable unless very fast, effectiveand reliable countermeasuresare taken.Its uniquecontrolprinciplehas sincebeenpatented.The inductivepower of 250 MVAr is provided by threethyristor-controlled reactors (TCRs), afourth, continuously energized TCR beingalways on standby 5 . Two identicaldouble-tuned filters, each rated at40 MVAr, take care of harmonics andsupply capacitive reactive power duringsteady-state operation.High availability is essential for the AuasSVC. If, for any reason, it should haveSpecial ReportABB Review21

V (pu)61.61.41.21.00.80.60.40.20V/I characteristic, showing the possible steady-state andtransient operating points of the SVC-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.2 2.5 3.0 3.5 4.0Capacitive I (pu) InductiveThe colored area represents continuous SVC operation. Above thisarea, the SVC can be operated up to 1.2 pu voltage for 3 s, up to 1.3 puvoltage for 400 ms, and up to 1.5 pu voltage for 300 ms.to be taken out of service, the 400-kVtransmission system could not be operatedwithout risking dangerous overvoltages.As a result, an availability figureof 99.7 % was specified, and this stronglyinfluenced the design, quality, functionalityand layout of its componentsand subsystems as well as of the SVCscheme as a whole.3 s400 ms300 msshould be thelast transformersin the Nam-Power systemto go into saturation.TCR reactorand valveEach TCRbranch consistsof two air-corereactors connectedon eachside of athyristor valve.The reactorshave specialexterior surfacesto protectthem from theeffect of sandstorms and sunin the harshdesert environment.A secondary voltage of 15 kV was chosenas an optimum value for both thethyristor valve and busbar design. Thethyristor valves consist of single-phasestacks of antiparallel-connected thyris-tors (16 thyristors, two of which areredundant, in each valve). Snubbercircuits (series-connected resistors andcapacitors) limit overvoltages at turnoff.The thyristors are fired electrically usingenergy taken directly from the snubbercircuit.An overvoltage protection device limitsthe voltage that can appear across thevalve, being triggered by control unitsthat sense the instantaneous voltageacross each thyristor level.Redundant TCR branchThree TCR units rated at 110 MVAr havebeen installed to cope with the Nam-Power network’s sensitivity to reactivepower and harmonic current injections.A fourth, identical TCR is kept on hotstandby. The SVC control system automaticallyrotates the current standbyTCR unit every 30 hours to ensure equaloperating time for all units.Redundant cooling systemAn unusual feature of the Auas SVC isthat each TCR valve has its own coolingsystem, making four in all. Thus, outagetime is minimized and availability is increased.A water/glycol cooling mediumis used to avoid freezing in case of aux-Operating rangeThe Auas SVC provides resonance controlover its entire operating range 6 , whichextends well beyond its continuous range.Controlled operation is possible all theway up to 1.5 pu primary voltage – a necessaryfeature for controlling the resonancecondition. Besides providing resonancecontrol, the SVC also controls thepositive-sequence voltage (symmetricalvoltage control) at the point of connection.Single-phase transformersFour single-phase transformers, includingone spare, are installed. Due to thehigh overvoltage demands made onthem during resonance these transformershave been designed with a lowerflux density than standard units; they22Special ReportABB Review

iliary power outages during the colddesert nights.Filter branchesThe required capacitive MVAr are providedby two 40-MVAr filter banks. Eachfilter is double-tuned to the 3rd/5th harmonicsand connected in an ungroundedconfiguration. The double-tuneddesign was chosen to ensure sufficientfiltering even in the case of one filterbecoming defective.Black-start performanceSince the SVC is vital for operation ofthe NamPower system, everything hasto be done to avoid the SVC breakertripping, even during a network black-Voltage / 400 kV (pu)71.81.61.41.21.00.80.6Real-time digital simulation. 400-kV line energized from the north, with and withoutthe new resonance controller0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0t (s)a)out. In such a case the network couldbe energized from the Eskom side andthe SVC would have to be immediatelyready to control a possible resonancecondition. To handle this task, the SVChas three separate auxiliary supplies,one of which is fed directly from theSVC secondary bus. The SVC is capableof standby operation with its MACH 2controller active for several hours withoutauxiliary power, and automaticallygoes into resonance control mode assoon as the primary voltage returns.BrefAdd (pu)BrefDI (pu)0.50.0b)-0.5-1.0-1.5-2.0-2.5-3.00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0t (s)0.50.0c)-0.5-1.0-1.5-2.0-2.5-3.00 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0t (s)a Voltage response, 400 kVRed Conventional PI controllerb SVC controller outputBlue Resonance controllerc Impact of resonance controllerWorst-case situation:energization from north to southThe worst–case scenario for the SVC andthe Nampower system is energization ofthe 400-kV line from the northern section(Auas substation). This system condition,which initiates the critical 50-Hz resonance,was therefore simulated in a realtimedigital simulator with and withoutthe new resonance controller. As shownin 7 the overvoltage that appears atAuas is 1.62 pu with a conventional PIcontroller. (The two resonance frequencies– 56 Hz and 81 Hz – that can beseen in the result correspond to the system’sfirst and second pole, respectively.)The new resonance controller has a considerableimpact on the system’s behaviorand the voltage controller’s additionalcontribution forces the SVC to becomeinductive. As a result, the peakvoltage appearing at Auas is reduced toa value of 1.32 pu.Special ReportABB Review23

8SVC performance. Results of a phase-to-ground fault in the Auas substation1.211pu1.0pu0pu00.80.64.5 5.0 5.5 6.0 6.5-1-2BrefDI4.5 5.0 5.5 6.0 6.5-1-2BrefADD4.5 5.0 5.5 6.0 6.5t (s)Voltage response, 400 kV SVC controller output Impact of resonance controllerThis extreme test was also performedin the field. Comparison of the simulationresults and the system performancetestshowsvery goodagreementand underlinesthe improvementcapabilityAs a result of installing the ABBSVC, the resonance problems thathad previously plagued theNamibian grid are a thing of thepast.of the new resonance controller underresonance conditions.Staged fault testAfter the Auas substation had beencommissioned, a phase-to-ground faultwas used to test various SVC controlfunctions and the interconnection protectionscheme. The performance ofthe SVC is shown in 8 . As the resultsshow, theSVC controlsthevoltageand theresonancecontrollerforces theSVC tobecome fully inductive in resonanceconditions. The fault is initiated att = 4.9 s and is cleared by openingthe faulty phase in the Auas-Kokerboomline. A single-phase auto-reclosureis initiated after 1.2 s, starting withthe breaker on the Kokerboom side.The overvoltage at Auas is reduced to1.14 pu.Easier cross-border power sharingAs a result of installing the ABB SVC,the resonance problems that had previouslyplagued the Namibian grid area thing of the past. Southern Africa’sstate energy sectors can now be moreeasily integrated and power more easilyshared. And the growing demand forpower – the motor driving the region’seconomic ambitions – can be moreeasily met.Rolf GrünbaumMikael HalonenStaffan RudinABB Power TechnologiesSE-721 64 VästeråsSwedenFax: +46 21 18 31 43rolf.grunbaum@se.abb.comReferences[1] R. Grünbaum, M. Noroozian, B. Thorvaldsson: FACTS – powerful systems for flexible power transmission. ABB Review, 5/1999.24Special ReportABB Review

TransformingtransformingAdvanced transformer controland monitoring with TEC Lars JonssonGetting the most out of electrical equipment isvital to energy enterprises in today’s increasinglyderegulated world. With power transformersmaking up a substantial part of thatequipment, it is little wonder that utilities put apremium on enhancing the lifetime and performanceof these industry workhorses.Conventional control and monitoring schemesrely on past results – good enough, perhaps,for routine maintenance and non-critical units,but not to keep transformers performing constantly,and unfailingly, at the highest level.Not so ABB’s TrafoStar Electronic Control(TEC) system. This models the actual state ofthe transformer, creating a ‘virtual copy’ thatprovides the parameters required to optimizecooling as well as the data utilities need forcondition-based maintenance.Power transformers at critical nodes inelectricity networks lead stressfullives. Reliability is everything. Loadpeaks – predictable as well as unexpected– generate high temperatures, whichshorten component lifetime. In the worstcase sudden failure can occur, causinghavoc in the network. It is because ofthis risk, and the penalties that can attachto it, that utilities give such a high priorityto controlling and monitoring the statusand condition of their transformers.This lets them intervene before failure ormalfunctioning can occur. Increasingly,for many utilities, the watchword is ‘earlydetection of failure conditions’.Enter the ‘intelligent transformer’Deregulation of the energy markets hasbrought about a paradigm shift andfocused attention on, among otherthings, asset management and remaininglife management. As a result, anincreasing number of power transformersaround the world are being equip-Special ReportABB Review25

1TEC receives the information it needs for transformer control from just a few multipurposesensors.tion and then comparing the measuredparameters with the simulated values.Discrepancies are detected and potentialmalfunctions and/or normal wear in thetransformer and its ancillaries are indicated.As ABB’s fully integrated control andmonitoring solution making use of oneoriginal set of multi-purpose sensorsand employing specific transformerdesign data, TEC is the latest addition toa product portfolio that already includesthe ABB T-Monitor. The T-Monitor is aproven retrofit solution that providesadequate predictive power by means ofeasily fitted add-on sensors and modelsthat require less detailed informationabout the transformer and its componentdesign.TEC architectureThe system hardware and softwarefeatures proven ABB technology andhas been designed to allow extra functionalityto be added in the future. Beingmicroprocessor-based, the systemhas more flexibility than a PLC andprovides a more stable platform than aPC solution.TEC gets its capability to control andmonitor not only from its superiorsoftware, but also from the fact that ithas unlimited access to all the informationit requires. It knows everythingped with monitoring devices. As thistrend intensifies and more and morefunctionality is added, transformers arelikely to play a new role – as ‘intelligentunits’ – in future transmission networks.The trouble with many transformermonitoring systems is that they are notable to control or make decisions andrecommendations based on the availabledata, forcing engineers to spend alot of time sorting and interpreting theinformation they receive. This is thestrength of TrafoStar Electronic Control(TEC) 1 . TEC receives all the informationit needs for transformer controlfrom just a few multi-purpose sensors;other necessary parameters are calculated.Thus, TEC adds only minimalcomplexity to the transformer.To achieve the goal of making powertransformers ‘intelligent’ and maintenance-free,ABB created and integrateda common electronic interface that exchangesinformation with the followingapparatus:Monitoring and diagnostics devices ofthe transformer and componentsTransformer control cabinetTap-changer motor-driveOverall protection systemThrough this interface, TEC provides exactstatus information to enable utilitiesto extend transformer lifetime and savecosts by reducing maintenance and increasingavailability.It does this by generating a model ofthe transformer and its working condi-2The main parameters can beviewed on-line on the TEC frontpanel or on a PC terminal.26Special ReportABB Review

3Start panel showing a transformer modelwith basic data4TEC users can easily access more detailed informationas well as transformer or tap-changer documentation.about your transformer. This ‘knowledge’begins with the transformerdesign data. Next, temperatures andloss-related parameters obtained fromthe transformer heat-run test are fed in.So much data is transferred to the TECsystem that it becomes a virtual transformercopy. Each transformer hasits own fingerprint, with all the parametersneeded for optimized control.The model created by TEC works insimulated conditions but reacts in thesame way that a real transformer would.The main parameters are processed inthe TEC cabinet and transferredto the station PC via a single opticfiber. They are made available to theoperator via easy-to-use software anda display.TEC and Industrial ITIndustrial IT [1] has been introduced byABB as an architecture for seamlesslyinterconnecting all our Group’s products,solutions and processes. More thanthat, it allows our customers, servicepartners and third parties to connectwith them too. Industrial IT enables thetotal integration of business processeswith real-time and lifetime data management.As a consequence, utilities will beable to substantially improve the efficiencyof their business.Utility assets, such as power transformers,are prime candidates for such realtimeintegration. And TEC is an idealmeans of integrating them. It will becertified to Level 2 (Integration), meaningthat it will not only be informationenabled and capable of connection toand working well in an Industrial ITsystem, but also be able to exchangeextended data, like status and maintenancedata, via defined protocols. Systemswith Industrial IT Enabled componentsoffer a variety of advantages,including ‘plug and produce’ capability.Disturbances are reduced at the sametime that flexibility is increased.Feature overviewTEC offers a whole range of functionsdesigned to let utilities use their transformersto the maximum. Until now,service criteria have been based on loadassumptions and the results of the lastservice. TEC changes all this. Real-timeinformation opens up new possibilitiesfor optimizing operation and maintenance.Cooling/overload forecastTraditionally, transformer cooling is atwo-step system, with the option of50 % or 100% capacity. With TEC, sixsteps are possible, according to load,ambient conditions and cooler status.The coolers are controlled individuallyand can be started prior to an anticipatedload increase. This reduces thermalstress and adds hours of operation atmaximum capacity.TEC advanced cooling control is basedon algorithms that calculate the heatlosses and the number of coolers requiredto dissipate them. It also keepstrack of the number of hours each fan isin operation and runs all motors accordingly.As input, TEC receives data onthe actual and/or predicted load andambient conditions. Armed with this information,the system is able to respondimmediately to load peaks, and thecooling capacity can be better adaptedto actual demand. Further, it can simulatethe results for a specific load conditionor forecast the maximum overloadduration based on the hot-spot results.Real-time status/availabilityThe parameters measured during serviceare compared with the simulated values.The transformer model detects discrepanciesand indicates potential malfunctionsand/or normal wear in the transformeritself, the cooling equipment andthe tap-changer.Real-time information from temperaturesensors and from optional moisture sen-Special ReportABB Review27

5TEC electronics – tried and testedtemperatures, up to three hot-spot temperatures,the apparent power and thetap-changer position and operations.More detailed information can be obtainedby clicking on the object on thetransformer model or by pressing one ofthe status information buttons.All of the transformer and tap-changerdocumentation, including instructionfilms, can be viewed on the PC in thecontrol room or any other place ofconvenience 4 .Tried and provenEnvironmental tests, hardware/softwarefunctional tests and on-site tests in variousparts of the world have shown thatthe system is well suited for substationenvironments.ABB’s extensive experience with electronicequipment in harsh industrial environmentshas also been incorporated inthe design of the TEC 5 . For example, itis EMC compliant and vibration proof.sors is stored by the TEC system. If required,a hydrogen detector can bemounted on the tank to obtain an earlyindication of potential problems in atransformer winding.A rolling LCD on the front panel showsthe main parameters together with athree-lamp status ‘traffic light’ (green/yellow/red). The same information canbe viewed on a PC terminal, either inthe substation control room or at aremote location 2 .LifetimeTemperature control, based on overloadforecasting and winding hot-spot calculations,allows the consumed lifetime tobe computed in accordance with the latestIEC and IEEE standards.Event recordingTEC also keeps track of transformertrips and alarms, recording the actualevents as well as the sequence to assistoperators in determining their rootcause.Condition-based maintenanceThe status traffic light identifies themost heavily worn contact in thetap-changer, based on the actual loadduring each operation. The user seeswhen the next service is due.Oil treatment is condition-based, beingdependent on the development of moistureas indicated by the temperatureand (optional) moisture sensor in thetap-changer compartment.Early warning is given of any increasein tap-changer temperature beyond thenormal value.Operation and updatesThe user interface runs in the Windowsenvironment. The PC start panel 3shows a transformer model with basicdata such as the top-oil and bottom-oilA modular systemTEC is the first of a generation, andABB continues to investigate new approachesand ways to improve thesystem as a whole and in part. Furtherparameters for the transformer, tapchangerand bushings will be includedin the future. TEC’s modular designmakes this easy, and provides theflexibility that will ensure its success asan innovative and cost-saving product.By giving utilities the means to monitor,and thereby optimize, the way theyoperate their power transformers, TECcan be said to be truly transformingtransforming.Lars JonssonABB Power TechnologiesPower TransformersLudvika, Swedenlars.y.jonsson@se.abb.comReference[1] C. Rytoft, B. Normark: Industrial IT and the utility industry. ABB Review 3/2002, 23–28.28Special ReportABB Review

Power SystemsRana MukerjiConsultingAmid the regulatory transformation that is revolutionizing the utility market,reliability and economics stand out as the factors driving financial andoperating performance. To get the best return on their assets and performat the highest level, utilities are turning to solutions that integrate thedomain competence of consulting experts with the very latest softwaretools. New methods for optimizing performance costs have been developedin the course of several recent projects undertaken by ABB.Power systems consulting is a keyABB offering, enabling customers toplan, operate and maintain their systemsin a more economical and reliable way.Consulting work in which ABB is engagedcovers a broad spectrum, and includes:Planning for grid upgradesSystem performance issues related tovoltage, thermal and dynamic stabilityconstraintsEvaluating and enhancing grid reliabilityForecasting demand growth for distributioncompaniesBenchmarking of utilities relative toglobal ‘best in class’ peer groupsAsset evaluation and reliability centeredmaintenance planningTechnical due-diligence in support ofmergers and acquisitionsThe ABB Consulting group is a globalteam of more than one hundred powersystems experts with local presence inthe USA, UK, Germany, Spain, Sweden,Italy, India and China. ABB consultantsare backed up by over 6000 product,systems and service specialists in locationsclose to our customers, enablingthe company to identify and implementtotal system solutions.Changes for the betterJust as the rest of the power industryhas changed dramatically within the lastdecade, the art and science of transmissionand distribution planning is fundamentallydifferent from what it wasten years ago. Deregulation and performance-basedregulations are changingthe framework within which plannersand system operators work. Considerationhas to be given to new technologieson both the load side and the supplyside. The changes cover the spectrumof regulatory policy, technology,competition and industry economics.In recent years, a strong global economyhas resulted in demand growth inmost companies’ service territories. Inthe majority of companies, even thosewith overall flat growth, there are pocketsof relatively strong load growth inthe system for which planners mustspecify the infrastructure. More thanever, utility planners need to be awareof the equipment installed in the system,as well as its current condition.Generally, customers also expect a levelof reliability as good as, or better than,the reliability they have been used to inSpecial ReportABB Review29

the past. An increasing number of customersoperate businesses today thatare sensitive to reliability and the qualityof service. It is therefore importantfor utilities to have the tools to systematicallyanalyze cost/performance tradeoffswithin the financial constraints imposedon them. Similarly, the benefits ofavailable funds should be maximized.This often implies changes to standards,guidelines and procedures.Interpreting such changes and developingnew optimization methods andstate-of-the-art software to assist utilitiesin meeting these challenges is whereABB has vast experience. In just the lastfive years, new methods for optimizingperformance costs have been developedthat allow the domain competence ofconsulting experts and software tools tobe integrated in a web-based data warehousingtool. These new methods let usfocus on the most cost-effective waysto obtain maximum performance for asystem and utilization of assets.The following two examples show howABB’s experience can be the key factorin creating optimal, cost-effectivesolutions for customers based on keyperformance indicators.Reuniting BerlinOn March 5, 1952, as a result of thepolitics of the time, the electrical supplysystem of Berlin was divided into twosections, one for the eastern and onefor the western zone. Now, five decadeslater, the two networks, like the twohalves of the city, are reunited, havingbeen incorporated in the German interconnectedgrid. For Berliner Kraft- undLicht (Bewag) AG, the utility responsiblefor running the network in thewestern half of the city, joint operationof the two networks posed certainproblems. Besides the obvious need forstandardization – different systemphilosophies had developed over theyears – it was also apparent that a conceptwas needed for the city’s electricitysupply in the longer term.Investigations were carried out to findan optimal concept for the reunited distributionnetworks of Berlin that tookall factors into account. Bewag andABB formed a joint planning group todevelop the approach. Its main objectivewas to make the two networksmore compatible so that the city wouldbe able to cope with future electricitydemand.One of the issues looked at especiallyclosely was the reliability of the downtownarea networks, and at ways toincrease it without making any basicchanges to the supply concept. In particular,it was necessary to find out if,and what, additional investments mightbe required to achieve the goal ofhigher reliability.With the help of advanced mathematicalmodeling of the system componentsand special programs for the calculations,certain system components wereloaded beyond their conventional nominalpower. This showed which componentscould be utilized more economically.As a result of this study, Bewagdecided to increase the capacity oftransformers and underground cablesused in the networks.Utility gets resultsThe second example involves an electricalutility company providing powerto several regions in Europe. In order tobenchmark some of their guidelines,practices and power quality indexes,they wanted a comparison with utilitiesin Germany and the United States thatwould identify ‘best practices’. To thisend, studies were carried out in theareas of maintenance, transmission anddistribution planning, and engineeringand operations.In addition to providing a benchmarkfor these four areas, ABB undertookreliability calculations for the utility’spower distribution system. This wasdone to obtain a baseline for its distributiondesign practices at the time, aswell as an on-site diagnosis of certainfacilities.Distribution transformer density data, imported from a utility’s transformer load managementprogram and used in load forecastingABB found differences between the utility’spractices and typical practices inGermany and the USA, especially in themaintenance area. It was seen that achange in procedures could result in30Special ReportABB Review

with the new planning methodologyand tailored to the company’s newgoals and needs.Seminars and workshops for over220 engineers, managers and supervisorsfrom 14 operating districts, toconvey the concepts and skills necessaryto implement the new approach.Load forecast study performed usinga commercially available GIS database asstarting pointconsiderable cost savings without significantlyaffecting reliability. The studyalso recommended use of some of thenewer probabilistic approaches to systemplanning which help minimize thecost of new investments.After receiving the study results, theutility indicated that it was “very impressedby ABB’s ability to set up a crossborderteam in such a short time tocope with a challenging project with avery tough deadline.”Business processes and assetutilizationIn another example, ABB instituted ‘budget-constrained’planning policies andmethods appropriate for a regulated US‘wire company’ operating in a competitiveenvironment. The project included:A review of all engineering planningand budgeting procedures, reliabilityrequirements, engineering criteria,planning guidelines, and appropriatestandards, as well as planning, budgetingand engineering results fromthe past ten years.Development and implementation ofa new planning/budgeting/projectprioritization method based on marginalbenefit/cost optimization usingcustomer service quality costs aswell as budget cost as an element ofperformance evaluation.Design of an entirely new planningprocess and organization, compatibleAnother project undertaken by ABB involvedinvestigating the operations andmaintenance history and procedures of aTexas utility’s underground distributionand transmission cable systems in theDallas, Fort Worth and DFW airport serviceareas. The investigation includedreliability assessments of the transmissionand distribution systems using anetwork model. Also included were inspectionsof parts of the utility cable networks,substations and pumping stations,as well as interviews with utility operations,engineering, and maintenance personnel.The investigation further includeda review of utility standards, guidelinesand documentation relevant to theoperation of the cable network.Power system performance researchAnother area in which ABB is active is inresearch into power system performanceand the development of new technologiesfor its improvement. In one suchproject, named ‘Wide Area Disturbance’,we examined, among other things, voltageinstability, overload and out-of-step.Based on this, we developed a newalgorithm for estimating the proximityto voltage collapse. The method employsonly local measurements – busvoltage and load current – and is simpleenough to be implemented in a numericalrelay. The relay’s estimation can beused for a number of applications, forexample to enhance local controllers(SVCs, etc) or to direct load shedding.Alternatively, the estimation can be sentto a computing center as support forsystem coordination.Other completed projects, eg ‘RobustControl of FACTS Devices’ and ‘Controlof Nets, Drives and Converters’, haveexamined the algorithms for dampingpower oscillations under uncertainoperating conditions. UncertaintiesScreenshot taken from a budget-constrainedplanning software simulationincluded transmission outages andvarying load profiles. New algorithmsand software for centralized anddecentralized robust controllers weredeveloped and tested by means ofsimulations on realistic system models.Backing up ABB’s consulting business isdomain expertise and field experienceaccumulated over decades in the powerindustry, plus a global presence thatallows us to bring best practices fromall over the world together to help ourutility customers improve their businessperformance.Rana MukerjiABB Power TechnologiesABB Inc.Raleigh, NC, USArana.mukerji@us.abb.comSpecial ReportABB Review31

The big pictureDetecting power system instabilities and optimizingasset utilization with Inform IT Wide Area Monitoring PSG 850Joachim Bertsch, Cédric Carnal, Andreas Surányi32Special ReportABB Review

Developments in the world’s power markets are compelling utilitiesto place greater emphasis on asset utilization in order to operatemore profitably. But there is an equal need, as the recent massiveblackouts in North America and Europe showed, to have safeguardsin place that ensure total reliability for the transmission networks.Increasing attention is therefore being given to the monitoring ofpower system dynamics. This requires information of higher accuracyand with update rates faster than those normally provided by traditionalSCADA systems. In addition, it has to be synchronized over awider geographical area than traditional protection systems allow.With the introduction of phasor measurement units and recent advancesin communication and computing it has become technicallyfeasible to take a wide area approach to monitoring power systemstability on-line. Inform IT Wide Area Monitoring PSG 850 was developedas a state-of-the-art platform for just such an approach.IT-based, it offers solutions designed to optimize asset utilizationas well as to prevent entire power networks from collapsing.The world has come to depend onelectricity so much that huge efforts– and investments – have to be made toensure that it flows uninterruptedly.Apart from having to find the capital forthis, the electric utilities are faced withanother problem: market pressures areforcing them to maximize their profitability.Together, these factors providea strong incentive for utilities to installtechnology that combines functionalityfor optimizing asset utilization and coststructures with that required to preventpower system outages. This is preciselywhat Inform IT Wide Area MonitoringPSG 850 – one of a family of PSG modules/packagesthat also include widearea protection and control (PSG 870),wide area measurement (PSG 830) andwide area connectivity (PSG 810) (seefigure on page 34) – was developed for.Inherent benefits of the PSG 850 solutioninclude:Transmission capacity enhancement,achieved by on-line monitoring of thesystem safety or stability limits.Power system reinforcement (investmentplanning), based on feedbackobtained during analysis of systemdynamics.Introduction of a coordinated approachto stabilizing actions in casesof severe network disturbance.Triggering of additional functions,such as var compensation.Better understanding of a system’sdynamic behavior.Installation of an early warning systemdesigned to prevent potentialblackouts.Data utilization in wide area monitoringMonitoring of entire power systems withPSG 850 is based on dynamic phasormeasurement – increasingly being seenas the ultimate in data acquisition technology.Phasor measurement units(PMUs), located in critical areas of a network,allow fast measuring of the voltageand current phasors (ie, their magnitudeand phase angles) and optimizeprocess control on the basis of a dynamic,Special ReportABB Review33

highly accurate system overview. Severalelectrical utilities have already deployedPMUs in their grids, mainly for manualdata acquisition and processing.A key feature of wide area monitoringsystems is the central acquisition ofdata from PMUs, enabling utilities toutilize phasor information wherever itis needed. PSG 850 provides the followingcustomized forms of data utilizationin support of utilities’ asset managementtargets.Monitoring of dynamic system behavior –stability assessmentAt present, power system operationtends to be based on static or quasi-dynamicinformation extracted from rmsmeasurements, mostly using SCADA systems.Phasor measurements at importantnodes help system operators gain adynamic view of the power system andinitiate any necessary stabilizing measuresin good time. Significant supportis provided by stability assessment algorithms,which are designed to take advantageof the phasor measurement information.This increases the efficiencyof power system operation and helps tomaintain security at the desired level.Monitoring of transmission corridors –congestion managementEnergy is often traded over the transmissioncorridors interconnecting thepower systems – an activity that addssignificantly to the cost, and thereforeprice, of energy in liberalized markets.However, the transmission capacity ofsuch corridors is often constrained bystabilityconcernsa 4 to 6 % increase in transmission capacityachieved by deploying a widearea monitoring system could help topostpone or even avoid major investmentsworth 10Phasor measurements at importantnodes help system operators gain adynamic view of the power systemand initiate any necessary stabilizingmeasures in good time.havingtheir origininuncertaintyabout theunderlyingsystemstatus. The traditional solution – toreinforce transmission path capacity byinstalling new lines – has the advantageof offering high availability, but alsothe substantial disadvantage that lineconstruction is time-consuming andrequires huge new investments.An alternative solution is to significantlyimprove asset utilization through widearea monitoring. This reduces uncertaintiesand, consequently, the operationalrisks. Under certain conditions, such aslower-than-assumed ambient temperatures,the dynamic capacity increase canbe significant. The smaller investmentmakes the ABB solutionfar more cost-effectivethan installing newlines. For example,to 100millionUSD.PSG 850is thereforealsoan importantdecision support tool for congestionmanagement and investment planning.Disturbance analysis and system extensionplanningThe continuous data storage functionalityprovided by PSG 850 is a veryvaluable source of information for theanalysis of incidents and disturbancesoccurring in the power system. Besidesimproving the efficiency of power systemanalyses, it helps to determine andeliminate the actual causes of such inci-34Special ReportABB Review

dents. This accurate identification providesa sound basis for the planning ofsystem expansions and future systemreinforcements.1Configuration of a wide area monitoring system with synchronized phasormeasurements from PMUs used as input for the system monitoring centerSystem platform overviewSystem monitoring centerGPS satellitePhasor measurement as basic technologyWide area monitoring systems are essentiallybased on new data acquisitiontechnology. Unlike conventional controlsystems, which use, for example, RTUsto acquire the rms values of currentsand voltages, a wide area monitoringsystem acquires GPS 1) -synchronized current,voltage and frequency phasor informationmeasured by PMUs at selectedlocations in the power system. Themeasured quantities include both magnitudesand phase angles, being timesynchronizedvia GPS receivers with anaccuracy of one microsecond. Untilnow, critical nodes in transmission gridshave usually been monitored using staticor quasi-dynamic data based on rmsmeasurements. Phasors, measured at thesame time, provide instant snapshots ofthe status of the monitored nodes. Bycomparing these snapshots, both thedynamicandsteadystate ofcriticalnodes intransmissionandsub-transmissionnetworkscan beobserved. The result is dynamic monitoringof the power systems.System architecture of the wide area1) GPS Global Positioning SystemPMUPMUmonitoring platformThe platform architecture for monitoringis made up of the following hardware:Phasor measurement unitsCommunication linksSystem monitoring centerPMUs are placed in the substations toallow the power system to be observedunder all the different operating conditions(network islanding, line or generatoroutage, etc). Some redundancy isprovided to secure this information inthe event of certain data being unavailable,forexampleWide area monitoring is essentiallybased on new data acquisitiontechnology, with GPS-synchronizedcurrent, voltage and frequencyphasor information measured byPMUs at selected locations.due toPMU outageorcommunicationfailure.The measureddataare sentvia dedicatedcommunication channels to thePSG 850’s system monitoring center(SMC) – a central computational unit inwhich the collected data are synchronizedand sorted 1 . This provides asnapshot of the power system’s status.In the case of meshed network topologies,the snapshot is then processedby the basic monitoring (BM) package,which is part of the SMC. BM denotesthe set of algorithms included in allinstallations of the wide area platformas the basis for different software applications.This solution package has thefollowing capabilities:PMUTransmission networkAbility to provide consistent inputdata for all PSG 850 applications.Fast execution, leaving sufficient timeto run additional applications withinthe sampling interval.Robustness – the system is resistant tothe poor quality of some of the inputdata (availability, range, synchronization)The reference phasor can be chosenfrom various points in the grid. Softwareapplications, which are linked to the BMoutput, address various dynamic phenomenaoccurring in power systems.They predict the state of the power systemand suggest appropriate action tobe taken by the system operators whenan emerging instability is detected. Anergonomic graphical user interface (GUI)2 displays the output information.Historical data can also be accessed,allowing phasor data to be retrieved forsubsequent analysis. A navigation facilityis provided for easy selection anddisplay of the required information.Implementation activities andadvanced software applicationsTo take full advantage of Inform IT WideArea Monitoring PSG 850, a step-wiseSpecial ReportABB Review35

2Example of graphical user interface display provided by PSG 850. The popup linemonitoring faceplate (on right) compares voltage phasors.Increased grid utilization, facilitated byon-line monitoring of critical nodes.Detection and elimination of causesof power quality problems, madepossible by the high accuracy of theunderlying system of measurement.Thorough investigation of criticalincidents.Provision of additional strategic informationfor the utility’s grid planningdepartment.As a result of this positive feedback, severalwide area monitoring pilot projectsare now having their status upgraded to‘ready for commercial exploitation.’Wide-ranging benefitsExperience with installed prototypesshows that wide area monitoring systemshelp to significantly improve gridutilization, especially during peak demandperiods. Just as importantly, theyfacilitate detection of the critical factorsinfluencing a network’s fundamentalstability.approach is recommended: First, theutility and the PSG 850 supplier carryout an initial study to identify typicalnetwork problems and the most endangeredof the areas in which the system isto be deployed. Afterwards, the appropriatemonitoring algorithms and mostsuitable locations for installing the PMUscan be chosen. ABB has developed acomplete set of algorithms that ensureoptimized procedures during the variousstages.The fundamental software modules includea GUI(with singlelinediagram,pop-up windows,trenddisplays),easily scalablePMUconnectivitypackage, data storage capability andexport functions for further analysis.The following software applications areoffered with Inform IT Wide Area MonitoringPSG 850:Advanced monitoringVoltage stability monitoring for transmissioncorridorsLine temperature monitoringPower oscillation monitoringFrequency stability monitoringControl action suggestionsCustomer feedback has been goodSeveral systems with up to 16 PMUshave already been installed or engineeredfor practical application in highvoltagepower grids. Feedback fromprototype applications on customersites is diligentlyrecorded,and continuestoconfirmimprovementsinpowersystem performance. Evaluation of thefeedback shows that customer benefitsinclude:Cost-effective grid operation basedon observation of critical networkareas.Maximum benefit is gained fromwide area monitoring when theutility and ABB jointly identifytypical network problems and themost endangered areas.When a wide area monitoring system isinstalled, utilities that operate powerlines at high load levels can reduce theircosts substantially by postponing investmentin new infrastructure while stillmaintaining high grid availability.In this context, Inform IT Wide AreaMonitoring PSG 850 goes well beyondthe capability of existing local monitoringand protection equipment. It raisesthe level of asset utilization and cansignificantly contribute to future costsavings in a utility’s long-term strategicinvestment planning.Joachim BertschCédric CarnalAndreas SurányiABB Power TechnologiesCH-5400 Baden/Switzerlandjoachim.bertsch@ch.abb.comcedric.carnal@ch.abb.comandreas.suranyi@ch.abb.com36Special ReportABB Review

Industrial ITand theutility industryClaes Rytoft, Bo NormarkABB’s Industrial IT has been discussed often in the pagesof ABB Review, and its benefits, especially for automation,manufacturing and production applications, have beenexplained in detail. But what about the utility industry?How is Industrial IT contributing to this important area ofABB business and how can the unique business environmentof the utility industry profit from it?The utility industry is undergoinga fundamental transformation. Thechange from a vertically integrated industry,often under national control andwith only limited competition, if any atall, to a fully competitive, deregulatedindustry is dramatic in all its implications.On top of all this, the product involved,electrical energy, is vital to thedevelopment of nations. The US Departmentof Energy has put this clearly intoperspective by stating:“Electricity is a cornerstone on whichthe economy and the daily lives of ournation’s citizens depend. This essentialcommodity has no substitute. Unlikemost commodities, electricity cannoteasily be stored, so it must be producedat the same instant it is consumed. Theelectricity delivery system must be flexibleenough, every second of the day andevery day of the year, to accommodatethe nation’s ever-changing demand forelectricity. There is growing evidencethat both private and public action isurgently needed to ensure our transmissionsystem will continue to meet thenation’s need for reliable and affordableelectricity in the 21st century.IT solutions will be a key area for utilitiesin this new and fast-changing market.Only IT solutions can successfullyprovide enough flexibility and intelligenceto accommodate changes in themarket such as price erosion, investmentuncertainty and demand for higherreliability.Price erosionThe introduction of competition has, inmost cases, led to significant reductionsin electricity prices, as in Europe, wherethe electric utility industry has beenundergoing restructuring for the last tenyears 1 .Industrial customers are usually the firstto benefit from increased competition.Subsequent opening of the individualconsumer market is accompanied bystrong pressure on electricity pricesacross the board; in Sweden more than30% of customers have changed theirelectricity supplier since reform wasintroduced just a few years ago.The consequences of the increasedcompetition are that the utilities haveto better utilize existing investments,which are very capital intensive, toenhance their value, and also ensure thehighest possible return on future investments.At the same time, operation andmaintenance costs are becoming morecritical.Investment uncertaintyIn a non-competitive environment,planners had only to consider the loadgrowth per region and structure theinvestments accordingly. The regulatoryframework and the customer base werestable and this made planning easy. Themain focus was on security of supply,and costs for investments, operation andmaintenance were simply passed on tothe consumer.With the unbundling of generation,transmission and distribution activities,totally new conditions were createdfor the utilities. Competition is normallyintroduced in the generation business,whereas transmission is often left regulated.Different models are applied todistribution, but as a rule the regulatorpressures the distributor to be com-Special ReportABB Review37

111010090807060petitive. This has resulted in a largeincrease in investment uncertainty.Electricity is fast-becoming the largesttraded commodity in the world. The keysto success in this marketplace are theability to master real-time market dataand information about the capabilitiesand limitations of resources, and havingefficient tools for asset management.One initial reaction of the utilities hasbeen to cut back on investments, butthis is not a sustainable strategy. Publicresponse to somespectacular blackoutsand supplyshortages has resultedin pressurefor more stringentregulation.Electricity price development for industrial customers in Europe 1995–2000(1995=100). The blue, green and red curves assume a 100%,

2The Aspect Object is a key element of ABB’s Industrial IT architecture.SwitchgearPower system installationReal-time aspectsAspect ObjectAspect Object modelbut could just as well be any third-partyor customer application such as Word,Excel, ERP, a web camera, or a ComputerizedMaintenance Management System(CMMS) 3 .advantages arise from combining theintegration with added functionality andoptimization.The integration functionality of theIndustrial IT architecture is unique inthat it allows logical integration ofThis, in turn, engenders entirely newconceptual solutions. It is well knownfrom other industries that when components,systems and solutions areadapted for integration, totally newand much more efficient solutions aremade possible.Normally, the first step in integrationis to copy the traditional products andsystems into one common system.Since the different functions can shareinterface and computing capability, asaving in both hardware and softwareis certain.3Applications communicate via the Aspect DirectoryAspectDirectoryactivexUI UI UIGIS OCS CMMSâMicrosoftCOMThe second step in the integration is tostart utilizing the available informationto build completely new functionalityin the integrated system. The biggestDatabaseDatabaseSpecial ReportABB Review39

4independent applications without requiringany changes to them. A practicalexample of this could be to integratean OCS system with a CMMS, thusallowing an operator to issue an errorreport in the CMMS when somethinghappens in the plant. The report can be5Integrating a SCADA/EMS system with a Computerized Maintenance ManagementSystem allows an operator to issue an error report in the CMMS when somethinghappens in the plant.OperatorPump alarmCheck control loopCheck cooling systemWrite error reportControlControlCooling systemError reportWork orderSpare partsCooling systemError reportinitiated by just right-clicking with themouse on the faulty object and thenselecting the CMMS Aspect 4 .In the ABB Object architecture, suchflexibility is provided by an AspectDirectory which interfaces betweenThe Plant Explorer lets users navigate through the information in a way theyare familiar with.applications. When an application isinstalled in the system it registers allinterfaces that it supports with theAspect Directory. When any applicationwants to perform an operation that involvesaction by other applications, itqueries this Aspect Directory for referencesto all interfaces that implementthe operation, and then invokes theseinterfaces, one by one.To copy and paste an object, for example,all applications that implementAspects defined for the object must beinvolved and perform their part of theoperation, each application copying andpasting its Aspect respectively.Industrial IT based automationplatformABB utilizes the Aspect Object technologyboth as an integrated part of thenew automation platform and as a solutionfor integration of hitherto independentapplications, thus providing animproved workflow for ABB customers.The automation platform will span traditionalfunctions such as DCS, PLC andSCADA functionality. In the platform,the Aspect Object system will be usedto keep track of all information aboutan object connected to the system, eg acontroller, where the different Aspectsmight be an alarm list, control logic,documentation, graphics, etc.Importantly, the operator is providedwith a tool with a familiar ‘feel’ 5 foreasy navigation through the informationhierarchy. This ‘Plant Explorer’ is abrowser that allows navigation throughthe various structures and viewing ofthe Aspects defined for each object.Optimization by integrating solutionsAdvantage may be taken of the addedfunctionality arising from an integratedsolution to optimize the performanceof the entire system. This opens upspectacular possibilities, such as combiningreal-time information and addedfunctionality. For example, starting fromProduction cost forecastingCapability limitations in productionStatic and dynamic capability, withmargins in the system for both40Special ReportABB Review

Information needed for demanddrivenmaintenanceInformation needed for disturbanceprevention and mitigation,it is possible for users to take thisinformation and start combining asfollows:Market prices, current and future.How can I combine this with productioncost forecasting?Demand forecasting. How can I usethis information together with capabilitylimitations, maintenance schedulingand disturbance prevention?Maintenance scheduling. How canthis be combined with market pricing,demand forecasting and capabilitylimitations to minimize the consequentialcost of maintenance?Capability limitations. How canthis be combined with static and dynamiccapability margins to ensuremaximum utilization without reducingthe reliability?Industrial IT for utilitiesIndustrial IT is an overall strategy for ABB with major benefits for the utility industries:A new, modern automation platform in which Aspect Objects is an integrated feature andwhich will be introduced for power plants, water applications and substation control andprotection.A unique integration architecture that will make it possible to integrate existing utilityapplications.A certification process that guarantees that ABB, and many third-party, products will fitseamlessly into the Industrial IT architecture.A new transparent naming strategy that makes it easy to understand ABB’s product andsolution offerings.Industrial IT certificationTo ensure all ABB products adhere tothe Industrial IT architecture, a certificationprogram has been launched. It isplanned to certify all ABB products,including all power technology devicessuch as transformers, switchgear, etc.By mid-2003 over 30,000 ABB productswere certified at the basic certificationlevel. More advanced certification levels(Information, Connectivity, Integrationand Optimization are foreseen) as wellas certification of solutions will follow.The certification program is open forthird-party products and it is ABB’sambition to establish the Industrial ITarchitecture as an industry de factostandard.Market introductionIndustrial IT for Utilities will be introducedto the market in a step-wise fashion,with products and solutions beinggradually certified to comply with thefour levels of Industrial IT compliance.The first, smaller power plant and waterautomation systems based on the newautomation platform are already up andrunning.A key goal in the introduction programis to develop new solutions around theAspect Object architecture.Structured customer offeringsAll offerings compliant with the IndustrialIT architecture will have a consistentnaming structure that is descriptivein its nature. That means that nameswill directly guide the reader to whateverapplication or use is addressed.For ABB’s utilities business, the namingpolicy has been applied according tothe following structure (with examples):Solution Portfolio (Industrial IT forPower Generation)Solution Suite (Industrial IT forCombustion Management)Solution (Industrial IT Carbon inAsh Monitor)Product (Control IT , Process Controller,AC 800M)Claes RytoftBo NormarkABB Power TechnologiesCH-8050 ZurichSwitzerlandclaes.rytoft@ch.abb.combo.normark@ch.abb.comReference[1] The ABCs of Industrial IT . ABB Review 1/2002, 6–13.Special ReportABB Review41

Cold storageThe battery energy storage system for Golden Valley Electric AssociationTim DeVries, Jim McDowall, Niklaus Umbricht, Gerhard LinhoferAlaskan winters are cold. Where temperaturescan drop to minus 50°C, power outages arevery bad news indeed. A reliable supply of electricityis given a high priority when yourwater pipes can freeze solid within hours if thepower goes down!One way to prevent this happening isto have an emergency power source feedenergy into the grid until back-up generationcan be made available. An economically andecologically more viable alternative to ‘spinningreserve’ – gas turbines kept running in case ofan emergency – is battery back-up. In Augustthis year, the world’s largest-ever batteryenergy storage system was inaugurated inFairbanks, Alaska. In addition to stabilizing thelocal grid, it will reduce power outages in thearea by 65%. A consortium led by ABBsupplied and installed the system.Golden Valley Electric Association(GVEA) is a rural electric cooperativebased in Fairbanks, Alaska, serving90,000 residents spread over 2200square miles. A reliable supply of electricityis essential to the local populationsince many residents live in remoteareas and winter temperatures can fallas low as minus 50°C. Back-up powertherefore has to be available in theevent of an outage.Traditional solutions for providing reservepower require building and maintainingtransmission and generation capacitywell in excess of normal demand.GVEA’s decision in favor of a batteryenergy storage system (BESS) reflects itscommitment to installing a system thatis a cost-effective and efficient alternativeto these solutions.15 important minutesAt the heart of the world’s most powerfulstorage battery system are two corecomponents: the converter, designedand supplied by ABB, and nickel-cadmium(Ni-Cd) batteries, developed by Saft.The converter changes the batteries’ DCpower into AC power, ready for transmissionover the GVEA grid. The batteriesconstitute the energy storage medium.They can produce up to 27 MW ofpower for 15 minutes, giving the utilityenough time to get back-up generationon line. While the BESS is capable ofproducing up to 46 MW for a shorttime, the client’s primary need is for thesystem to cover the 15-minute periodbetween sudden loss of generation andstart-up of back-up generation.Although the BESS is initially configuredwith four battery strings, it can readilybe expanded to six strings to provide afull 40 MW for 15 minutes. The facilitycan ultimately accommodate up to eightbattery strings, providing flexibility that42Special ReportABB Review

will allow the client to boost output orprolong the useful life of the systembeyond its planned 20 years.System and project requirementsThe final specification required that thevendor provide a turnkey solution andguarantee for twenty years that the BESScould supply 40 MW for 15 minutes,with a 4 MW/min ramp-down after the15-minute mark. The system is requiredto be capable of operating in all fourquadrants (ie, the full power circle) andto provide continuous, infinitely adjustablecontrol of real and reactivepower over the entire operating range.The specification also required that theBESS be able to operate in an automaticmode, as GVEA does not plan to manthe facility.Rated output had to be provided for thefollowing power system characteristics:Nominal voltage of 138 kV (1.0 pu)Normal sustained voltage of 0.90 pu(min) and 1.1 pu (max)Normal frequency of 60 Hz, withnormal deviation of +/- 0.1 HzSustained frequency range of 59.0 Hz(min) and 60.5 Hz (max)Seven operating modesThe BESS is able to operate in sevendistinct modes:Var support: The BESS provides voltagesupport for the power systemunder steady-state and emergencyoperating conditions.Spinning reserve: In this mode, theBESS responds to remote generationtrips in the Railbelt system. It is initiatedat a system frequency of 59.8 Hz,with the BESS loading to full outputat 59.4 Hz if system frequency continuesto drop. Spinning reserve has thehighest priority of all the modes andwill interrupt any other mode theBESS is operating under.Power system stabilizer, included todamp power system oscillations.Automatic scheduling, used to provideinstantaneous system support inthe event of a breaker trip on either atransmission line or a local generator.The BESS has thirty independentlytriggered inputs, which will be tied remotelyto the trip circuits of breakers.Scheduled load increase: This is initiatedand terminated by SCADA andputs the BESS in a frequency andvoltage regulation mode to allow itto respond to the addition of largemotor loads.Automatic generation control: In thismode the BESS is capable of operatingby AGC, similar to that of rotatingmachinery.Charging: The SCADA dispatcher cancontrol the MW rate at which the BESSwill be charged and when charging isto start after a BESS discharge.The batteryThe Alaskan BESS battery comprises13,760 Saft SBH 920 high-performancerechargeable nickel-cadmium cells,arranged in four parallel strings to providea nominal DC link voltage of 5000 Vand a storage capacity of 3680 Ah. Thecells are built into 10-cell modules formounting in a drive-in racking system.An aisle between the racks providesinstallation and service access for aswing-arm fork truck.The complete battery weighs some1300 tons and the hall in which it islocated measures 120 meters by26 meters – about the size of a soccerfield. The initial battery configurationhas four individual strings operatingin parallel, but can be expanded toaccommodate eight strings. Each stringhas 3440 cells connected in series.The battery features a pocket plate constructionwith thin, high-performanceplates. This design allows the full 20–25year life to be attained without anyloss of the beneficial characteristics ofNi-Cd batteries. The type of cell usedcan deliver 80% of its rated capacity in20 minutes.Ni-Cd pocket plate cells can withstandrepeated deep discharges with littleeffect on battery life. The graph in 1shows the cycling characteristics of theSBH battery.The chosen design has several advantages:Compact arrangement: More rackdepth can be utilized, minimizing thespace taken up by aisles.1100001000100Easy installation: 90% of the connectionsare made in the factory; onlythe inter-module connections aremade on site.Quick change-out: If there is a problemwith an individual cell, the modulecontaining that cell can be replacedby another complete modulein less than 30 minutes 2 .Minimum power losses: 99% of theinter-cell connections are made withsolid copper bars; power lossescaused by flexible cable connectionsare therefore minimized.Spill isolation: The cells sit on a plasticgrating, allowing spills to drain intothe base of the module. The traycan hold the electrolyte content of allten cells.World recordCycling characteristics of theBESS battery.No. of charge/discharge cyclesvs depth of dischargeNumber of cycles0 10 20 30 40 50 60 70 80 90Depth of discharge (%)During commissioning tests, ABB’s powerconversion system and the Saft battery setan unofficial world record by achieving a peakdischarge of 26.7 MW with just two strings inoperation, making use of the short-time overloadcapability of the battery modules. Thismakes the Alaskan BESS more than 27 percentmore powerful than the previous recordholder – a 21-MW BESS commissioned byPREPA (Puerto Rico Electric Power Authority)at Sabana Llana, Puerto Rico in 1994.Special ReportABB Review43

2Battery module, comprising 10 cells, on the moveData collection and transfer are organizedhierarchically. The lowest-leveldevice in the hierarchy is the sentryunit. There is one for each 10-cell module,and its task is to measure the modulevoltage, cell electrolyte level andcell internal temperature. Each sentryunit reports its collected data to asergeant module. Every string has itsown sergeant module, which also measuresthe string float current. In turn,the sergeant module reports its collecteddata to the supervisory computer,which analyzes and displays the data.This computer is also responsible forforwarding summary data to the HMIand is the main terminal for BESS personnelwho need to access the monitoringsystem.Optical couplers carry the data from thesentry units to the data bus, which isinsulated to withstand a minimum of5000 V. 5560 readings are taken every30 seconds – a total of 5.8 billion readingsper year. These numbers can bedoubled if required.The electrical systemFour battery strings are currently installed3 . All preparations have beenmade for extension at a later stage, withup to eight battery strings possible. Everystring (and sub-string) can be switchedoff and completely isolated from the restof the system by DC switches. In addition,two disconnectors allow separationof the battery and the DC link of theconverter when maintenance work hasto be carried out on the batteries. Theconverter can then remain in operationand provide reactive power to the gridfor voltage control. Filter circuits in theDC link eliminate the risk of resonancesat higher frequencies should any harmonicsbe generated in the grid by nonlinearloads. The voltage source converterat the heart of the electrical systemcomprises standardized PEBBs (PowerElectronic Building Blocks). One doublestackPEBB in NPC (Neutral PointClamped) connection forms a singlephaseH-bridge 4 Four H-bridges areinstalled per phase, for a total of twelvesingle bridges. The stacks are cooled bydeionized water in a closed-loop circuit.A PE liner on the inside of the modulecase (between the battery cells andmetal tray) provides the necessary insulation.Each module is fitted with a selfcontained,single-point filling system,allowing all 10 cells to be topped up ina single operation without removing themodule from the rack.Battery monitoring systemThe battery monitoring system was suppliedby Philadelphia Scientific Inc. Itmeasures, records and reports the modulevoltage, string current, cell electrolytelevel (one cell per module) andcell internal temperature (also one cellper module).Each bridge is connected to its dedicatedtransformer winding. The voltagecontributed by the bridges is added inthe transformer by series-connecting theline-side partial windings, resulting in avoltage wave shape similar to the qualitythat could be expected from rotatingmachines. Voltage limiters prevent anyovervoltages due to sudden load rejectionsor possible disturbances in theelectric grid from damaging the DC link.The converter and transformers havebeen designed and built to handle thetotal power should the battery beextended from four to eight strings ata later stage.44Special ReportABB Review

3Basic diagram of the electrical systemto 138 kV/60 Hz gridBattery strings 1 to 4Filter circuits12 x 2-phasemodules4 units3 x 1-phasetransformers4 units4 units2 unitsVoltagelimiter unitto 138 kV/60 Hz gridThe active switching devices used in theconverter are integrated gate commutatedthyristors (IGCTs), an advanced type ofgate turn off thyristor (GTO). Comparedwith other devices that can be turned off,IGCTs have the advantage of lower conductionand switching losses, plus superiorswitch-off characteristics that allow asnubberless converter design.Ease of serviceability was a primaryconsideration during the mechanicaldesign. All power semiconductors inthe stack are readily accessible, allowingeasy replacement.4Power and reactive powerperformanceThe system is designed for four-quadrantoperation. It can charge as well asdischarge the battery and it can absorbBuilding block. A double-stack water-cooled PEBB in NPC connection,forming one H–bridgeAdvantages of this converter designinclude:The three-level medium-voltage modulesare proven, highly reliable products.Low FIT values are obtainedwhen these modules are used.Use of double-stack modules shortensthe distances between the powersemiconductors, keeping stray inductanceslow, and reduces the spacerequired for the complete converter.Since the clamp diodes and capacitorsare integrated in the semiconductorstack, the stray inductance in theclamp circuit is also minimized,allowing use of higher IGCT switchoffcurrents.Using a single clamp for two phasesreduces the need for bulky and costlyclamp inductors and resistors.AC 1AC 2D C +R symC C +C C –D C –D C +R symC C +C C –D C –=Special ReportABB Review45

Reactive power [pu]Inductive Capacitive51.510.50-0.5-1-1.5reactive power from or supply reactivepower to the grid. Each of these modesis possible with the DC link voltagevarying as the battery’s charging conditionchanges.The operating range of the system interms of active and reactive power for90% and 100% of the nominal grid voltageis shown in 5 .6Operating range of BESSP/Q diagram1 pu corresponds to 40 MVA-1.5 -1 -0.5 0 0.5 1 1.5ChargeDischargeActive power [pu]= V_grid = 100% = V_grid = 90%Overview of control and protection systemThe control systemLocal system control is provided by anABB SPIDER MicroSCADA humanmachine interface (HMI) based on theMicrosoft Windows operating system 6 .The system is operated via pictures,windows and function keys using amouse and a keyboard. Sequence andclosed-loop control as well as overallprotection are provided by ABB’sprogrammable high-speed controller(PHSC), which can be programmedusing the graphic function plan programFUPLA. The PHSC is well provenand its reliability has been shown to besuitable for both system control andprotection in numerous applications.The converter control incorporates thefollowing functionality:Sequence controlControl of the main breakersSignal conditioningProcessing of measurement signalsFast current control for ride-throughin the event of external faultsPower and reactive power controlLoad managementInterlocking of local control andSCADA/RTU controlRedundant protection functionsBESS – a stabilizing factorWhile fulfilling its overall mission ofreducing power outages in the Fairbanksarea, the Alaskan BESS has specificbenefits in the areas of transmission anddistribution, generation and strategicplanning:Transmission and distribution benefitsinclude voltage regulation, first swingstability and loss reduction.In the generation area the BESS offersspinning reserve, ramp-rate constraintrelief, load following, black starts, loadleveling, and a reduction in deferredturbine starts.Strategic benefits include improvedpower quality, reduced demand peaks,and enhanced service reliability throughreduced power supply generated outages.The principal benefit, however, isthe ability of the BESS to instantly contributeto system stability following theloss of a major transmission line orgenerator. The spinning reserve it provideshas the potential to allow generationunits to be run at lower levels orbe shut down entirely, resulting in significantsavings. Almost instantaneousactive power is available. This is importantin cases where the BESS has toramp up before the impact of a generatorloss becomes noticeable at the pointof common coupling.Battery monitoringsystemLocal HMI(ABB MicroSCADA)GVEA SCADARTUProgrammable High Speed ControllerProtectionTim DeVriesGolden Valley Electric Associationtrdevries@gvea.comControlConvertercooling unitJim McDowallSAFTjim.mcdowall@saftamerica.com118Battery stringConverter Transformer 138 kVswitchgear138 kV gridNiklaus UmbrichtGerhard LinhoferABB Automation TechnologiesCH-5300 Turginiklaus.umbricht@ch.abb.comgerhard.o.linhofer@ch.abb.com46Special ReportABB Review

XLPERFORMANCEHigh-voltagecable technologyBjörn Dellby, Gösta Bergman, Anders Ericsson, Johan KarlstrandDeregulation of the electricity supply markets and growing environmental awareness are creatingexciting new markets for power transmission solutions based on extruded cabletechnology. At the same time, improvements on allfronts are extending the use of XLPE (cross-linkedpolyethylene) insulated cable systems up to500 kV. Today’s cable system applications areoften competitive with overhead lines, whilenew manufacturing methods are enablingsubmarine cables with integrated opticalfibers and flexible joints to be supplied inlonger lengths than ever before. Further developmentof extruded insulation systems is alsocontributing to the success of ABB’s innovativeHVDC Light TM concept.High-voltage cable systems rated220 kV and above have becomepart of the very backbone of moderndaypower transmission infrastructure.This importance carries with it, however,a special responsibility on the partof the suppliers to ensure that thesystems exhibit the highest reliabilityand, because of the high electricalstresses at such voltage levels, that thecables and accessories are properlycoordinated.Deregulation – changing the rulesIn today’s deregulated electricity markets,the rules that used to govern generation,transmission and distributionhave changed for both the power utilitiesand the suppliers. Suddenly, it isthe customer who is in the spotlight.Accordingly, the market has to listenmore to public opinion, and there isa strong possibility that this will includea call for a less ‘visible’ T&Dinfrastructure.All the actors in this new market haveto reduce their costs and at the sametime guarantee high reliability for thetransmission and distribution systems.A likely scenario is that new cable interconnectionswill be built and operationalmargins will be utilized morefully in order to get maximum technicaland economic benefit from the electricalnetwork.Extruded cable systems have a majorpart to play in this new, competitiveenvironment, especially when it comesto replacing overhead lines with undergroundcables. XLPE cable systemscosts have decreased during the lastdecade and are likely to fall even further.At the same time, XLPE cable performancehas increased enormously.The new message is therefore thatXLPE cable systems are able to competewith overhead lines, technically, environmentallyand commercially. This isparticularly true in the voltage range of12–170 kV 1 .Extruded insulation – performanceand improvementsThe well-established trend toward asmaller insulation thickness will continue,resulting in a leaner cable withmany advantages, among them longerdispatch lengths, fewer joints, easierSpecial ReportABB Review47

CR13025201510501986 1988 1990 1992 1994 1996 1998 2000installation, and reduced thermal contraction/expansionof the insulating material.Experience accumulated duringEHV XLPE cable system development,improvements made in materials andprocesses, and the excellent servicerecord of XLPE, have reduced the thicknessof cable insulation to 12–15 mmfor 132-kV cable systems. This placesthe XLPE cable systems versus overheadline transmission scenario in anew light, where the cable solutionoften can be an attractive alternative.Underground cables versusoverhead linesThere are, of course, many operational,security, environmental, reliability and2Comparison of cost ratio (CR) for XLPE cable systems and overheadtransmission lines400 kV130 kVeconomic parameters that distinguishXLPE cable systems from overheadlines [1]. For modern XLPE cable systems,the reduced cost ratio and environmentaland reliability benefits arethe most obvious and important considerations.Due to their larger crosssectionalareas, cables usually exhibitfewer losses per MVA than comparableoverhead lines. A summary of the benefitsof XLPE cable systems is given inthe table on page 52.The ratings of the overhead lines aresometimes dictated by high winterloads, which include a lot of electricalheating equipment. During hot summerdays the overhead line carries someRating of overhead line (OHTL) versus underground XLPE cable. The dashed lineindicates that higher powers could be transmitted if the daily load cycle profile istaken into account.50% less electricity than in winter, makingthem less attractive if load profileshave to be smoothed out in the future.In areas where there are many air-conditioningunits, for example, the benefitsof XLPE underground cables makethem a genuine alternative 2 .Underground transmission lines alsohave a better overload capacity forperiods of time shorter than 90 minutesdue to the high thermal mass of thesurrounding soil.Qualification of 400–500 kV cablesystemsThe IEC emphasizes the importance ofreliability and coordination of the cablesand accessories by recommending thatthe performance of the total system,consisting of cable, joints and terminations,be demonstrated. The comprehensivetest program, including a ‘prequalification’test, is described in detailin IEC 62067.ABB qualified as a supplier of cablesystems for the 400-kV voltage level in1995.Quality, materials and manufacturingOnly certified suppliers are contractedto deliver essential materials. All ABBmanufacturing sites for HV cables andaccessories are ISO 9001 and 14001 certified.The XLPE cable core is producedon a dry curing manufacturing line. Thecable insulation system, including theconducting layers, is extruded in a singleprocess using a triplex extrusioncross head located, together with thethree extruders for the insulating andconducting materials, in a clean-room 3.AmpacitySoilAir/soil temperatureXLPE cablesOHTLCable design4 shows a 400-kV XLPE cable. Thecable’s copper conductor, which has across-sectional area of 2500 mm 2 , isdivided into five segments to reduceskin effect losses. ABB uses segmented(Milliken) conductors made of strandedwires for cross-sections greater than1000 mm 2 . For cross-sections smallerthan 1000 mm 2 , the conductors arehighly compacted to obtain a rounder,smoother surface.48Special ReportABB Review

The metallic screen consists of copperwires on a bedding of crepe paper to reducethe mechanical and thermal impacttransferred to the insulation. The numberof wires and the total cross-section dependon the short-circuit requirements ofthe network. Longitudinal water tightnessis achieved by filling the gaps betweenthe screen wires with swelling powder.3Vertical extrusion of XLPE cable insulationExternal protection against mechanicalimpact and corrosion is provided by atough, extruded, laminated sheath madefrom HDPE (high-density polyethylene).A bonded metal foil on the inside of thesheath stops water from diffusing intothe cable.The resulting lean, low-weight cable hasseveral advantages: a greater length ofcable can be wound onto any givendrum; high eddy-current losses in thecable sheath are avoided; the currentcarryingcapacity is optimized.Possible oversheath options are:An extruded conductive layer forouter sheath measurementsAn extruded flame-retardant layer forextra safety in hazardous environmentsAnother option the cable design offers isspace-resolved temperature monitoringwith optical fibers. The fibers are containedin a stainless-steel tube, approximatelythe same size as a screen wire,which is integrated in the cable screen.Monitoring the temperature in this wayenables the cable load to be optimized.screen, which reduces the inducedscreen currents and losses in the AC cablesystem. The complete cable systemwith joint, outdoor terminations and GISterminations, fulfills the requirements ofIEC 62067 in every respect.4Testing of 220–500 kV cablesystemsIn the case of medium-voltage cables itis usual to think in terms of components.Even if these come from differentsuppliers, they can be joined together400-kV XLPE cable. The copper conductor is divided into five segments to reduceskin effect losses.Cable accessoriesIn the early 1990s ABB developed prefabricatedjoints for HV and EHV cableswhich are totally dry, ie with neithergaseous nor liquid materials, and maintenance-free.The main electrical partscan therefore be pre-tested in the factory,speeding up on-site installation andreducing the attendant risks. The jointshave integrated sheath insulation inorder to comply with the CIGRE recommendationcontained in Electra 128,which requires them to withstand impulsevoltages of 125 kV between thetwo joint sections and 63 kV to earth.This permits cross-bonding of the cableSpecial ReportABB Review49

and the system as a whole will stillwork. This is why limits are given forthe electrical stresses in the constructionrequirements in IEC 60502.HV and EHV cables and accessories, onthe other hand, are designed as systems.No construction requirements exist forcables for these voltage levels, just thetest requirements in IEC 60840 andIEC 62067.400-kV XLPE cable projectsIn 1996 ABB received an order from thepublic utility Bewag (now VattenfallEurope) to supply and install a 400-kVXLPE cable system in a 6.3-km longunderground tunnel in the center ofBerlin. The ventilated tunnel is situated25 to 35 meters below ground and has adiameter of 3 meters 5 . The cable system,with a 1600 mm 2 segmented copperconductor, has a transmission capacity of1100 MVA and forms part of a diagonaltransmission link between the transmissiongrids west and east of the capital.The cable is installed with the threephases arranged vertically, one abovethe other, on specially designed cablesaddle supports7.2 metersapart, with ashort circuitproofspacerin the middleof each span.The cable routewas dividedinto nine sections,eachapproximately 730 meters long. GISterminations were installed at the twosubstations and the new ABB joint wasused to interconnect the cable lengths.The laid cable consists of three maincross-bonded sections, with three minorsections within each main section.The cable circuit went into service inDecember 1998.Greater lengths of lowweightXLPE cable canbe wound onto anygiven drum, while higheddy-current losses inthe sheath are avoided.The Bewag utility subsequently awardeda second 400-kV XLPE cable contractto ABB, this time for a 5.4-kmlong system, again in an undergroundtunnel. This cable circuit completes thediagonal link betweenthe transmissiongrids west andeast of Berlin, andwas handed overto the customer inJuly 2000.Further 345–400 kVcable projectsawarded to ABBinclude orders for 200-km XLPE cables,accessories and installation. Commissioningof these projects is scheduledto take place during 2003–2004.New submarine cable projectsIn 1998 ABB was awarded the ChannelIslands Electricity Grid Project, whichreinforces the power supply fromFrance to Jersey and, for the first time,connects Guernsey to the Europeanmainland grid. The submarine part5400-kV cable system in a 6.3 km underground tunnel running through Berlin’s city center50Special ReportABB Review

of this project was completed in July2000.The main components delivered for theproject were:Submarine cables between Franceand Jersey and between Jersey andGuernsey (approx 70 km)Underground cables on Jersey andGuernseyGIS substationsNew transformers and reactors6Storage of submarine cable prior to layingThe two submarine cables are of thesame basic design, ie three-core, separatelead-sheathed, and with tripleextrudedXLPE insulation. Each has afiber optic cable with 24 fibers integratedin it for system communication andinter-tripping. The cables have doublewire armor (ie, an inner layer of tensilearmor and an outer, so-called rockarmor) to protect them from damagethat could be caused by tidal currentsand fishing.The cables have a diameter of approximately250 mm and weigh about85 kg/m in air.Both cables were delivered by the factoryin their full lengths 6 .Because of the risks posed by fishingactivities, the cables between Jersey andGuernsey and the fiber optic cables betweenJersey and France were jetted intothe seabed for extra protection.Another submarine cable project is theMa Wan and Kap Shui Mun Cable,which crosses a channel in Hong Kong.Due to the heavy traffic in this channel,it was decided to forgo conventionalinstallation of the 132-kV and 11-kVsystems, which would probably havedisturbed shipping even if modern techniqueswere used. The problem wassolved by drilling under the seabed andinstalling ducts through which thecables were pulled. This has the extraadvantage of allowing upgrades to becarried out in the future.Separate control systems were installedto monitor operation of the cable link,which was completed in 2003.A new submarine cable project hasrecently been awarded to ABB byAramco. The cable, which is 53 kmlong, is rated 110 kV with 3 ž 500 mm 2copper conductors. It will be commissionedin 2004.HVDC Light TMHVDC Light TM , which was launched in1997, is another ABB innovation in theT&D field that incorporates advancedHV cable technology. High VoltageDirect Current (HVDC) cables are employedfor bulk power transportationover long distances, mainly underwater.Traditional cable technology is basedon paper insulation systems impregnatedwith highly viscous oil. While thesecables have many technical advantages,the manufacturing process is slow andthe end-product is mechanically sensitive.The industry had therefore beenlooking for a long time for an extrudedHVDC cable of the kind used in ACsystems.With HVDC Light [2], ABB has introducedto the market an extruded cablesystem, together with new transistorbasedconverters, that makes HVDCSpecial ReportABB Review51

EnvironmentGrid securityEconomyOperationNo visual impactLow/no electromagnetic fieldsHigh level ofpersonnel safety,low risk of flashover in airGood working conditionsNot affected by wind, snow, ice,fog, etcNothing can be stolenLow maintenanceMinimum investment forlake/river crossingsLand use minimizedValue of land/buildingsunaffectedHigh availability,few faultsUsually low losses/MVAHigh short-time overloadcapacityBenefits of underground transmission linestransmission competitive even at lowpower ratings. The first commercialsystem, a link rated at 50 MW, wasinstalled on the Swedish Island ofGotland, where it transmits power froma wind power plant to the town ofVisby [3].Other major projects that have beencompleted are:The Directlink, rated 180 MW at80 kV, which transfers power betweenthe states of New South Walesand Queensland in Australia.The Murraylink, rated 200 MW at150 kV, built to transfer power betweenVictoria and South Australia [4].The Cross Sound Cable, rated330 MW at 150 kV, which transferspower between New England andLong Island.The latest HVDC Light project, to supplypower to an offshore platform in theNorth Sea (Troll A), is due to be commissionedin 2004. (See article startingon page 53.)Applications for HVDC Light include:Feeding of isolated loads (eg, offshoreplatforms)Asynchronous AC grid connectionTransmission of power from smallgeneration units (eg, wind powerplants)DC grids with multiple connectionpointsNetwork reliability enhancementthrough voltage stability and blackstartsTomorrow’s electrical infrastructure –here nowExtruded cable systems are available astotal solutions, with a ‘cradle to grave’supplier commitment. Such systems areturnkey offerings in the commercial aswell as the technical sense. They maystart with the permit application, continuewith the removal of the overheadlines and the supply and installation ofthe cable system, and end with theenvironmentally friendly disposal of theold equipment.Complete cable system applications canalso be seen as intelligent combinationsof monitoring equipment, converters,load-sharing devices, series and/orshunt compensation devices. Financing,too, can be arranged; here, leasing anda new type of availability guaranteecould resolve several commercial uncertainties.Together, these ‘thumbnail’ sketchesof the future add up to a new customer-value-basedmarket. Extrudedinsulated cable system applications aredestined to play a key role in thisevolving market by meeting not onlythe transmission and distribution networkrequirements of today but alsothose of tomorrow.Dr. Björn DellbyGösta BergmanDr. Anders EricssonJohan P. KarlstrandABB Power TechnologiesHigh Voltage CablesSE-371 23 KarlskronaSwedenbjorn.dellby@se.abb.comReferences[1] D. Karlsson: Comparison of 130 kV XLPE cable systems and OH lines – loading capability, reliability and planning criteria. CIGRÉ 2002.[2] K. Eriksson: HVDC Light DC transmission based on voltage sourced converters. ABB Review 1/98, 4–9.[3] M Byggeth, et al: The development of an extruded HVDC cable system and its first application in the Gotland HVDC Light project. JICABLE 1999.[4] T. Worzyk, et al: The Murraylink Project – the first commercial 150 kV extruded HVDC cable system, JICABLE 2003.52Special ReportABB Review

Powering Trollwith HVDC LightTom F. Nestli, Lars Stendius, Magnus J. Johansson, Arne Abrahamsson, Philip C. KjaerWith its compressors, motors andelectrical systems devouring manytens of megawatts, an offshoreinstallation can be a power-hungrybeast indeed. The onboard gasturbines or diesel generators thatusually supply this power, however,manage no more than about 25%efficiency – way off the dazzling75–80% efficiencies of, say, landbasedcombined cycle powerplants. This inefficiency isn’t justcostly in terms of excessive fuelconsumption, either; high emissionscan rack up the cost stillfurther, for example where CO 2taxation applies.Troll A platform (Photo: Øyvind Hagen, Statoil)Now, new technologies from ABB are making it easier thanever before to deliver electrical power to offshore installations,lowering operating costs and reducing environmental impactat the same time. Seventy kilometers off the Norwegian coast,two of these technologies – HVDC Light and Motorformer– are helping to power 40-MW compressor units on Statoil’sTroll A platform without any local power generation.Special ReportABB Review 53

On most offshore installations, thepower generators and large compressorsare driven by onboard gas turbinesor diesel engines with total efficienciesthat can be as low as 20–25 %even under ideal conditions. As aresult, fuel consumption and CO 2 emissionsare unnecessarily high. Ever sincethe Kyoto Protocol, which allows tradingof greenhouse gas emissions, highCO 2 emissions have become a costfactor. On top of this, as on the Norwegianshelf, there may be CO 2 taxation,making emissions costly evenwithout trading.If the electrical power for all this equipmentcan be supplied from shore, theCO 2 emissions of offshore installationsare eliminated, saving operators a considerablesum of money. But that isn’tall; transmitting electrical energy fromshore is also more efficient in terms ofequipment maintenance, lifetime andavailability.The overall environmental bonus ofeliminating low-efficiency offshorepower plants is considerable. A landbasedcombined cycle gas powerplant, which utilizes the gas turbine’swaste heat, can have an efficiency ofas much as 75 to 80 %. Even if highlosses of 10 % are assumed for a longtransmission line to an offshore installation,the saving will still be significantfor most installations.1HVDC Light and Motorformerjoin the offshore clubTroll A is the largest gas productionplatform on the Norwegianshelf. Some 40% ofNorway’s total annual gasproduction comes from TrollA, which can produce up to100 million cubic meters ofgas per day. Today, the reservoirpressure drives the gas to the onshoreprocessing plant at Kollsnes, where thecondensate, water and gas are separated.The gas is then compressed andtransported through pipelines to theEuropean continent 1 .As the gas is taken out of the reservoir,the pressure inevitably decreases. Thismeans that to maintain productioncapacity, offshore precompression of thegas will eventually become necessary.ABB has been awarded two contracts aspart of Statoil’s Troll A PrecompressionProject: a US$ 185 million contract forthe compression equipment and a US$85 million contract for the electric drivesystems for compressors. The new installationis due to go into commercial operationin the fall of 2005 as part of a programintroduced to maintain and expandthe platform’s production capacity.Choosing conventional systems for thisproject would have meant that gas turbineswould drive the compressors. Inthat case, it is estimated, annual emis-Gas from Troll A is processed at Kollsnes before being transported to theEuropean continent.sions of some230,000 tons ofCO 2 and 230 tonsof NO x would result.Besides theirimpact on the environment,the CO 2taxation in effecton the Norwegianshelf means that suchemissions would also bea significant cost factor.Working with Statoil, ABB developed analternative system 2 based on two innovativeABB technologies – HVDC Lightand Motorformer. These have beensuccessfully employed on shore since1997 and 1998, respectively, but neverbefore on an offshore installation ortogether as an electric drive system. Thesystem uses power from the onshoreelectrical grid to drive the compressorson Troll A, thus eliminating greenhousegas emissions from the platform.HVDC Light – rectifying, invertingand controllingHVDC Light [1], by using series-connectedpower transistors, enables voltagesource converters to be connected tonetworks at voltage levels higher thanever before for power transmission,reactive power compensation and harmonic/flickercompensation.On Troll A, an HVDC Light converter(inverter) feeds the variable-speed synchronousmachine driving each compressorwith AC power obtained byconverting the incoming DC, which istransmitted from shore over submarinecables. As their speed is variable, thecompressors are supplied with power atvariable frequency and voltage, rightthrough from zero to maximum speed(at 63 Hz) and from zero to maximumvoltage (56 kV), including starting, accelerationand braking. The drive systemsperform equally well at each endof the frequency spectrum. Small filtersat the converters’ outputs keep themotor winding stress at a safe level.The inverter control software is adaptedfor both motor speed and torque control.The motor currents and voltagesand the rotor position are measured and54Special ReportABB Review

2From the rectifier station at Kollsnes, subsea HVDC cables transmit power to the Troll A Platform, where the inverter station andMotorformer are located. Two identical systems are to be installed.KollsnesSubseacableTroll A platform132-kV switchboardRectifier stationHVDC LightcableInverter stationMotorformerPrecompressorPowertransformerHVDC Lightrectifier70 kmHVDC Lightinverter40 MW56 kVGearused together with an advanced modelof the machine’s electromagnetic parametersto calculate converter switchingpulses in much the same way as forsmaller industrial variable-speed drives(ACS 600/ACS 1000/ACS 6000). Unitypower factor and low harmonics areassured, along with a sufficiently highdynamic response, over the motor’sentire operating range. Protection andmonitoring of the converters and synchronousmachines, as well as controlof the excitation converter feeding thelatters’ field winding, are handled byABB’s well-proven Industrial IT HVDCControl, MACH 2.HVDC LightIn the past, high-voltage DC links have beenused almost exclusively to transmit very highpowers over long distances. HVDC Light [1]is a new transmission technology based onvoltage source converters that extends theeconomical power range of HVDC transmissiondown to just a few megawatts.HVDC Light also offers power qualityimprovements, for example reactive powercompensation and harmonic/flicker compensation.Thanks to fast vector control,active and reactive power can be controlledindependently, with harmonics kept low,even in weak grids.Overall control of the rectifier station atKollsnes is also handled by the MACH 2.There is no need for communication betweenthe rectifier control system onland and the motor control system onthe platform; the only quantity that canbe detected at each end of the transmissionsystem is the DC link voltage. Asthe DC link cannot store much energy,the motor control system is designed tofollow even rapid changes in powerflow at the opposite end without disturbingmotor operation. Nuisance trippingis generally kept to a minimum.The HVDC Light converter for Troll isbased on a two-level bridge withgrounded midpoint. Only extremely lowground currents are induced duringsteady state and dynamic operation, thisfeature being one of the main reasonsfor using HVDC for the power supply.No cathode protection of any kind hasto be provided for this installation.HVDC Light cable – the power carrierThe HVDC Light concept includes a furtherinnovation: the HVDC Light extrudedpolymer cable. The shift in high-voltageAC technology from paper-insulatedto extruded polymer cable was the incentivefor ABB to develop and producean extruded cable offering the samebenefits – flexibility and cost-effectiveness– for HVDC transmission.Troll A’s importance as a major gas producercalled for an extremely reliabletransmission link. The actual cable hasa 300-mm 2 copper conductor surroundedby a very strong and robust polymericinsulating material 3 . Wateringress is prevented by a seamless layerof extruded lead, over which there aretwo layers of armor – steel wire wovenin counter helix – to provide the requiredmechanical properties. This designensures that the cable has thestrength and flexibility necessary forlaying in the North Sea. The two electricdrive systems require an HVDCLight cable system with two cable pairsMotorformerMotorformer [2] features conventional rotor,exciter, control and protection technologies.Most of the stator technology is also conventional– the exception is the winding, which ismade of XLPE-insulated cable. The stator’scable slots are designed for low electricallosses, high-strength cable clamping,efficient cooling and simple installation.The first Motorformer to go into commercialoperation, at the AGA plant in Sweden,has verified the many benefits of using HVcable technology in large electric motors.Motorformer is suitable for most applicationswhere conventional technology is used today.Special ReportABB Review55

3HVDC Light extrudedsubmarine cable, with doublearmoring (80 kV rating)(one for each drive), physically separatedfrom each other on the sea floor.The two cables in each pair are operatedin bipolar mode, one having a positiveand the other a negative polarity.To make sure that the cables will notbe damaged by anchors or trawling,they are laid in trenches on the sea bedformed by water jetting, or coveredwith rocks where this is not practicable.Motorformer drives the compressorsFollowing the introduction in 1998 ofnew, innovative cable winding technology,ABB’s engineers soon began toconsider the possibility of using HVcable windings in place of conventionalwindings in electrical motors in orderto radically increase the motors’ voltageratings. Such a motor can then be connecteddirectly to the HV grid, doingaway with the need for a costly stepdowntransformer.The first product to be based on thisprinciple was an HV cable-wound generator.Shortly afterwards, the same conceptwas applied to motors, resulting inthe development of a synchronous machine,dubbed Motorformer (see panelon page 55). The first unit was installedin 2001 at an air separation plant inSweden, where it drives a compressor.This motor is directly connected to a42-kV bus. In the meantime, ABB offersHV motors of this kind for voltages upto 70 kV. Work is currently under wayto develop units rated at 150 kV.Apart from eliminating the step-downtransformer and related switchgear,Motorformer reduces the total systemlosses by as much as 25% 4 . Beingepoxy-free, it also has important environmentalbenefits, including easy recyclability.And fewer components meanhigher system reliability and availability,plus reduced costs for service, maintenanceand spares.A challenging environment forhigh-voltage equipmentOffshore equipment design is constrainedby the need to keep both footprintand weight to a minimum. HVDCLight and Motorformer offer importantadvantages in precisely these areas:Smaller filters and the absence of synchronouscondensers make HVDCLight more compact and lighter thantraditional HVDC systems.No large, heavy transformer is requiredto connect the Motorformerto the HVDC Light converter.4InputpowerUse of Motorformer TM eliminatestransformer losses (A). Only motorlosses (B) remain.ConventionalsystemABMotorformersystemBShaftpowerallowed to come into contact withhigh-voltage equipment.Environment: The high-voltage equipmentmust be protected from thedamp, salt-laden sea air.Availability: Given the daily productionof gas worth US$ 10–15 million, highequipment availability is essential.HVDC Light and Motorformer are innovativetechnologies with all the qualitiesneeded to power offshore platformsfrom shore for maximum economicaland environmental benefit. Troll A isthe first such platform anywhere to bepowered in this way, the electric drivesystem being part of a program tomaintain and expand production capacity.The elimination of CO 2 emissionsand a smaller equipment footprint arejust two of the benefits enjoyed byStatoil as a result.Dr. Tom F. NestliMagnus J. JohanssonABB Automation Technologiestom.f.nestli@no.abb.comOther design considerations in connectionwith this project were:Safety: Troll A produces large quantitiesof hydrocarbon gas, which is notLars StendiusArne AbrahamssonDr. Philip C. KjaerABB Power Technologies[1] G. Asplund, K. Eriksson, K. Svensson: HVDC Light – DC transmission based on voltage sourced converters. ABB Review 1/1998, 4–9.[2] G. L. Eriksson: Motorformer – A new motor for direct HV connection. ABB Review 1/2001, 22–25.56Special ReportABB Review

SwePol Linksets new environmentalstandard for HVDC transmissionLeif Söderberg, Bernt AbrahamssonSix cable links – all of them HVDC (high-voltage direct current) – arecurrently in service between the power grids of continental Europeand the Nordic region, with another five planned. The latest to bebrought on line is the SwePol Link, which connects the electricitynetworks of Poland and Sweden. It is unique in that, unlike previousinstallations that depend on electrode stations to transmit the returncurrent under ground or under water, it usescables to carry this current.The reason for all these links is thevital need to secure power systemreliability in each of the participatingcountries. They make it easier to optimizepower generation in an area inwhich different countries use differentmeans of power generation and havedifferent power demand profiles overa 24-hour period. Wet summers in theNordic region result in a considerablepower surplus, which can be sold tocountries that rely on more expensivefossil fuel-fired power plants. Conversely,any surplus power can be soldback during periods of low load.Power system reliability in the region isincreased by the addition of new HVDCcable links. In the event of grid disruptions,the rapid power balancing abilityof these links can be used to compensatefor fluctuations in frequency andvoltage. For example, it is technicallyfeasible to reverse the entire 600 MWpower throughput of the SwePol Linkin just 1.3 seconds, although this is nota feature that will be used in practice.Nevertheless, a typical emergency powermeasure could call for a DP ramp-up of300 MW within a few seconds to preventgrid failure if the voltage in southernSweden drops below 380 kV.All previous links of this kind use electrodestations off the coast to transmitthe return current under the sea, andthis has worked perfectly well. The firstsuch cable link was laid in 1954 betweenVästervik, on the Swedish mainland,and the Baltic island of Gotland.Since then, the power rating has beenincreased and the original mercury arcvalves in the converter stations havebeen replaced with thyristor valves.In the case of the SwePol Link, returncables were chosen as an alternativeto electrodes in order to pacify localresistance to the project, particularlyaround Karlshamn. The environmentalissues that were raised during planningof this link may also apply to futureinstallations.Lower emissions benefit theenvironmentThe power link between Sweden andPoland is the latest example of thegrowing economic cooperation betweenthe countries bordering the Baltic Sea.The cable, which was taken into commercialservice in June 2000, is a steptoward the large-scale power distributionpartnership that is known as theBaltic Ring [1].The new link allows power generationto be stabilized in both countries, wherethe seasonal and daily variations in demandcan differ considerably. The surplusthat builds up in the Nordic regionduring wet years has already been mentioned.In a really cold year it makesfinancial sense for this region to importPolish electricity generated from coalrather than start up a condensing oilfiredpower plant or a gas turbine.Polish imports of electricity via the linkwill in turn reduce environmental impactin that country. The predicted annualnet import of 1.7 TWh is expectedto reduce emissions from Polish powerplants by 170,000 tonnes of sulfur dioxideand 1.7 million tonnes of carbondioxide, according to calculations by theSwedish power company Vattenfall.Special ReportABB Review57

1KarlshamnBornholmBaltic SeaSwePol Link between Swedenand Poland.RonnebyKarlskrona1 x 2100 mm 2HVDC2 x 630 mm 2ReturnUstkaDarlowoThe power cable (blue) and the return cables(red) run on the same route, spaced 5 to 10 mapart in shallow water and 20 to 40 m apart indeep water.Poland’s forthcoming admission tothe EU will reinforce measures to reduceits enviromental impact, therebypromoting the import of Swedishhydropower.2RinghalsMalmöThe 250-km SwePol Linkexchanges power between 400-kVAC grids in Sweden and Poland.HemsjöKarlshamnSlupskKrajnikOskarshamnDunowoGdanskThe converter stations are near Karlshamn insouthern Sweden and at Slupsk, 12 km fromthe Polish coast.Cable company is set upSwePol Link AB was formed in 1997 toinstall, own and operate the cable linkbetween Sweden and Poland. It is apower transmission company that willsell electricity transmission servicesacross the link.A Polish subsidiary was formed in1998 to handle the local business. Onthe Swedish side the link will be usedprimarily by state-owned Vattenfall,although other companies will be ableto sign transmission agreements withSwePol Link.The new link is approximately 250 kmlong. It runs from Stärnö, just outsideKarlshamn in Sweden, past the Danishisland of Bornholm, and returns to landat the seaside resort of Ustka on theBaltic coast of Poland 1 , 2 .The Swedish converter station was sitedat Stärnö because a 400-kV station andthe Swedish main grid are nearby. Thisavoided having to build new overheadlines that would have marred theSwedish countryside. The Polish converterstation 3 is connected to thePolish 400-kV grid at Slupsk, about12 km from the coast.The link involved around 2500 manyearsof work for ABB, primarily at itsplants in Ludvika and Karlskrona. Bothstations are unmanned, although on-callpersonnel will be able to provide coverageat short notice.DC circuitThe land-based power grid is, of course,an AC system. However, for long underwaterlinks DC is the only viable solutionon account of the high capacitanceof submarine cables.Most cable links are monopolar systems,in which the return current is carriedthrough the ground and the sea.Power is transmitted over a high-voltagecable. It is a common misconceptionthat sea-water carries the returncurrent because of its high conductivity.However, most of the current travelsat a considerable depth through theearth.In the case of the SwePol Link the returncurrent is carried by two insulatedcopper conductors rated at 20 kV. Theuse of these conductors eliminates theneed for environmentally controversialelectrodes.The high-voltage cable 4 is around140 mm in diameter, of which the centralconductor takes up 53 mm. Insteadof being solid, this consists of coppersegments to make it more flexible.The segments are shaped individually,then rolled as a unit to achieve an effectivecopper cross-section in excess of99%. The rest of the cable consistsof various layers of insulation, sealantand armor. The 250-km long cable ismade up of four sections which are laidindividually and joined by the layingbarge.Visible parts of the linkThe visible parts of the link are thetwo converter stations at Stärnö andSlupsk. Located just a small distancefrom the center of Karlshamn, theStärnö station is next to an oil-firedpower plant that completely dominatesthe landscape. By siting the tall valvebuilding in a former quarry some10 meters deep, the station’s impacton the skyline is reduced even more.The power cables run 2.3 km from thestation to the sea.At the Polish end, the valve building isa prominent, but by no means ugly,landmark in the flat agricultural countryside.The Slupsk station is just over20 meters high and is situated about12 km from the Polish coast.Both the high-voltage and return cablesrun underground almost all the waybetween the stations. On land thisrequired clearing a five-meter wideswathe through the landscape when thecables were being laid. This will soonbe hidden, partly thanks to forest replanting.At sea about 85% of the cablecould be laid in a trench about onemeter deep to avoid damage by trawlersand anchors.The converter stations cannot only beseen, but heard too. This is because the58Special ReportABB Review

3Valve building in the Slupsk (Poland) converter stationof their lives and it is essential thattheir sense of direction remain unimpaired.Back in 1959 a study was carried outto determine how the Gotland cablehad affected the marine environment[2]. This was followed by exhaustivestudies on the Fenno-Skan link (Sweden–Finland)and the Baltic Cable(Sweden–Germany) [3]. The reportswere unanimous: marine life is affectedneither by the magnetic field nor byany chemical reactions. The facts speakfor themselves. Eels continue to findtheir way to the Baltic Sea, despitehaving to cross seven cables on theway [4, 5].eddy currents that flow in all powertransformers generate noise at a frequencyof 100 Hz. Converter stationsalso produce higher-frequency noisethat can be irritating to people livingnearby. It was clear that special soundproofingwould be necessary. Followingcalculations and measurement of thenoise level and noise propagation, thetransformers and reactors were enclosed.The filter capacitor cans are equippedwith a noise-reducing device.A magnetic field with minimal effecton the surroundingsWhenever electricity is transmittedthrough a conductor it generates amagnetic field around it. Since DC isused, the field is of the same type as theearth’s natural magnetic field. This iscompletely different to the AC fieldsnormally produced, for example,around overhead lines.Measurements have shown that the magneticfield around the cable at a distanceof six meters is equal in strength to theearth’s natural magnetic field, while at adistance of 60 meters its intensity dropsto just one tenth of that field.The magnetic field resulting from thecombination of 1 + 2 cables varies withthe depth and relative spacing of thecables. It is not practicable to lay thehigh-voltage cable at the same time asthe two return cables, which meansthat they cannot be laid right next toeach other. They also have to be separatedbecause of the heat they generate.In shallow water the HV cable islaid 5–10 meters from the returncables. The resulting magnetic fieldmeasured on the surface of the sea istypically 80% of that obtained around ahigh-voltage cable in a monopolarinstallation. The equivalent figure at100 meters depth with 20–40 metersseparation is typically 50%.Further away from the cables there isan even greater percentage reductionin the magnetic field, added to thefact that the absolute value of the magneticfield at this distance is insignificantcompared with the earth’s magneticfield. Thus, the use of returncables has no major effect on magneticfield strength. And, anyway, modernships no longer depend on magneticcompasses.But what are the possible effects onanimal life? Experience with previouscable links has shown that they donot affect fish or other marine organisms.Nor do they affect the vital homingability of eels and salmon. Thisis especially important since these fishmigrate regularly during the courseNo chlorine formationThe originally proposed monopolarsolution, which would have used electrodesto transmit the return currentundersea, has been replaced by analternative solution in which returncables form a closed circuit. Any concernsabout chlorine formation havetherefore been entirely eliminated,since no electrolysis can occur.34841 Conductor2 Conductor screen3 Insulation4 Insulation screen5 Metal sheathSwePol Link power cable, rated600 MW and 450 kV DC. Itsoverload capacity is 720 MW attemperatures below 20°C.1256796 Protection/bedding7 Reinforcement8 Armor9 ServingSpecial ReportABB Review59

Metal objects on Swedish coast that could have been affected by the SwePol LinkObject length Distance from electrode ExampleMore than 25 m Less than 5 km Cable supportMore than 200 m 5 – 10 km Sewage pipe Ø 1.2 mMore than 1000 m 10 – 20 km 10-kV cableThe electrodes that would have beenused have an anode made of fine titaniummesh and copper cables for thecathode. The following competing reactionstake place at the anode:2 H 2 O Þ 4H + + O 2 (g) + 4e -2 Cl - Þ Cl 2 (g) + 2e -(g) in the above formulae indicates thatthese elements are in gaseous form.The amount of chlorine gas generateddepends on the temperature, thechloride content of the seawater andthe reaction energies. It reacts almostexclusively with water as follows:Cl 2 (g) + H 2 O Þ HClO + Cl - + H +At low pH the hypochlorous acid thatis formed could be ionized, but in seawaterit mostly occurs in molecularform. In time it breaks down into itscomponent parts.There was a suspicion that the chlorinegas and hypochlorous acid that are formedwould react with biological materialin the vicinity of the electrodes, resultingin the formation of compounds such aspolychlorinated hydrocarbons, which includePCBs. Studies on the Baltic CableDistrict heatingCopper shield around buildingMore than 5000 m 20 – 50 km Protective shield (Cu)have ruled out this concern [3]. No accumulationof organic chlorine was observedin the surrounding biomass.To put things in the right perspectiveit is worth comparing the described processwith the common chlorination ofdrinking water, in which the hypochloriteconcentration is at least 100 timeshigher than the value measured at theanode.No corrosionThe return cables used for the SwePolLink eliminate the risk of corrosion, andthis would seem to be the only tangibleadvantage they offer.DC cable links that use electrodes dolead to leakage currents in the earth. Thereturn current passing through the earthtakes the shortest path. On its route betweenthe electrodes some of the currentmay pass through long metal objects,such as railway tracks, gas pipes and cableshielding. Electrolytic reactions couldoccur between this metal and its surroundings,possibly leading to corrosion.During the planning of the SwePol Linka list was therefore made of all the metalobjects that could be at risk (see table).Objects that are at risk of corrosion dueto leakage currents require some formof active protection, such as sacrificialor cathodic protection.The return current can also find a routethrough other power distribution systemsthat have multiple earth pointsclose to the electrode. This gives rise toa DC component in the AC grid, whichcan lead to undesirable DC magnetizationof transformers. The problem cangenerally be solved by modifying thegrounding of the AC system.Benefits versus costUsing the described return cables does,of course, have some advantages,among them the reduced magnetic fieldstrength along the cable route and thefact that they cause neither chlorine formationnor corrosion of undergroundmetal objects. And they also allowed asolution that addressed the environmentalconcerns of various groups of society.In any final count, however, thesebenefits have to be measured againstthe extra cost. In the case of the SwePolLink, for example, they added about 5%to the cost of the project.Leif SöderbergSwedPower ABSE-162 16 StockholmSwedenleif.soderberg@swedpower.vattenfall.seFax: +46 (0) 8 739 62 31Bernt AbrahamssonABB Power TechnologiesSE-771 80 LudvikaSwedenbernt.abrahamsson@se.abb.comFax: +46 (0) 240 807 63References[1] The making of the Baltic Ring. ABB Review 2/2001, 44–48.[2] W. Deines: The influence of electric currents on marine fauna. Cigré study committee no 10, 1959.[3] Anders Liljestrand: Kontrollprogram bottenfauna, bottenflora (Inspection program: bottom flora and fauna). Baltic Cable. Marin Miljöanalys AB,1999.[4] Håkan Westerberg: Likströmskablar, ålar och biologiska kompasser (DC cables, eels and biological compasses). Fiskeriverkets Kustlaboratorium,1999.[5] E. Andrulewicz: Field and laboratory work on the impact of the power transmission line between Poland and Sweden (SwePol link) on the marineenvironment and the exploitation of living resources of the sea. Sea Fisheries Institute Report, Gdynia, Feb 2001.60Special ReportABB Review

50 yearsHVDCABB – from pioneer to world leaderGunnar Asplund, Lennart Carlsson, Ove TollerzIn 1954, at a time when much of Europe was busy expanding its electricity supply infrastructureto keep pace with surging demand, an event was quietly taking place on the shores of the BalticSea that would have a lasting effect on long-distance power transmission. Four years earlier, theSwedish State Power Board had placed an order for the world’s first commercial high-voltagedirect current (HVDC) transmission link, to be built between the Swedish mainland and the islandof Gotland. Now, in 1954, it was being commissioned.50 years on, ABB proudly looks back at its many contributions to HVDC technology. Since thelaying of that early 90 kilometers long, 100-kV, 20-MW submarine cable, our company has goneon to become the undisputed world leader in HVDC transmission. Of the 70,000 MW of HVDCtransmission capacity currently installed all over the world, more than half was supplied by ABB.With the arrival of the electric lightbulb in the homes and factoriesof late 19 th century Europe and theUSA, demand for electricity grew rapidlyand engineers and entrepreneursalike were soon busily searching forefficient ways to generate and transmitit. The pioneers of this new technologyhad already made some progress – justbeing able to transmit power a fewkilometers was regarded as somethingfantastic – when an answer to growingdemand was found: hydroelectric power.Almost immediately, interest turnedto finding ways of transmitting this‘cheap’ electricity to consumers overlonger distances.First direct, then alternating currentThe first power stations in Europe andthe USA supplied low-voltage, direct current(DC) electricity, but the transmissionsystems they used were inefficient. Thiswas because much of the generated powerwas lost in the cables. Alternating current(AC) offered much better efficiency,as it could easily be transformed to highervoltages, with far less loss of power.The stage was thus set for long-distancehigh-voltage AC (HVAC) transmission.In 1893, HVAC got another boost withthe introduction of three-phase transmission.Now it was possible to ensurea smooth, non-pulsating flow of power.Although direct current had been beatenat the starting gate in the race to developan efficient transmission system,engineers had never completely givenup the idea of using DC. Attempts werestill being made to build a high-voltagetransmission system with series-connectedDC generators and, at the receivingend, series-connected DC motors – allon the same shaft. This worked, but itwas not commercially successful.AC dominatesAs the AC systems grew and power increasinglywas being generated far fromwhere most of its consumers lived andworked, long overhead lines were built,Special ReportABB Review61

The problem was solved in 1929 by aproposal to insert grading electrodesbetween the anode and cathode. Subsequentlypatented, this innovative solutioncan in some ways be considered asthe cornerstone of all later developmentwork on the high-voltage mercury-arcvalve. It was during this time that Dr.Uno Lamm, who led the work, earnedhis reputation as ‘the father of HVDC’.The Gotland linkThe time was now ripe for service trialsat higher powers. Together with theSwedish State Power Board, the companyset up, in 1945, a test station at Trollhättan,where there was a major powerplant that could provide energy. A 50-kmpower line was also made available.Analog simulator used in the design of the early HVDC transmission systemsTrials carried out over the followingyears led to the Swedish State PowerBoard placing, in 1950, an order forequipment for the world’s first HVDCtransmission link. This was to be builtbetween the island of Gotland in theBaltic Sea and the Swedish mainland.over which AC at ever-higher voltagesflowed. To bridge expanses of water,submarine cable was developed.Neither of these transmission media waswithout its problems, however. Specifically,they were caused by the reactivepower that oscillates between the capacitancesand inductances in the systems.As a result, power system plannersbegan once again to look at thepossibility of transmitting direct current.Back to DCWhat had held up high-voltage directcurrent transmission in the past was,first and foremost, the lack of reliableand economic valves that could convertHVAC into HVDC, and vice versa.The mercury-arc valve offered, for a longtime, the most promising line of development.Ever since the end of the 1920s,when the Swedish ASEA – a foundingcompany of ABB – began making staticconverters and mercury-arc valves for voltagesup to about 1000 V, the possibilityof developing valves for even higher voltageshad been continually investigated.This necessitated the study of new fieldsin which only a limited amount of existenttechnical experience could beapplied. In fact, for some years it wasdebated whether it would be possibleat all to find solutions to all the variousproblems. When HVDC transmissionfinally proved to be technically feasiblethere still remained uncertainty as towhether it could successfully competewith HVAC in the marketplace.Whereas rotating electrical machinesand transformers can be designed veryprecisely with the aid of mathematicallyformulatedphysicallaws, mercury-arcvalve designdepends to alarge degreeon knowledgeacquiredempirically.As a result, attempts to increasethe voltage in the mercury-vaporfilledtube by enlarging the gap betweenthe anode and cathode invariablyfailed.Following on this order, the companyintensified its development of the mercury-arcvalve and high-voltage DC cable,while also initiating design work onother components for the converter stations.Among the equipment that benefitedfrom the increased efforts weretransformers, reactors, switchgear andthe protection and control equipment.Even when HVDC transmissionfinally proved technically feasible,it was doubted for a long timewhether it could compete withHVAC in the marketplace.Only some of the existing AC systemtechnology could be applied to the newDC system. Completely new technologywas thereforenecessary.SpecialistsinLudvika,led byDr. ErichUhlmannandDr. HarryForsell, set about solving the many verycomplex problems involved. Subsequently,a concept was developed for the Gotlandsystem. This proved to be so successfulthat it has remained basically unchangedright down to the present time!Since Gotland is an island and thepower link was across water, it was62Special ReportABB Review

During the 1960s several HVDC linkswere built: Konti-Skan between Swedenand Denmark, Sakuma in Japan (with50/60 Hz frequency converters), theNew Zealand link between the Southand the North Islands, the Italy – Sardinialink and the Vancouver Island linkin Canada.Early mercury-arc valve for HVDC transmissionalso necessary to manufacture a submarinecable that could carry DC. It wasseen that the ‘classic’ cable with massimpregnated paper insulation that hadbeen in use since 1895 for operationat 10 kV AC had potential for furtherdevelopment. Soon, this cable wasbeing developed for 100 kV DC!Finally, in 1954, after four years of innovativeendeavor, the Gotland HVDC transmissionlink, with a rating of 20 MW,200 A and 100 kV, went into operation.A new era of power transmission hadbegun.The original Gotland link was to see28 years of successful service beforebeing finally decommissioned in 1986.Two new links for higher powers havemeanwhile been built between theisland and the Swedish mainland, onein 1983 and the other in 1987.The largest mercury-arc valve HVDCtransmission link to be built by thecompany was the Pacific Intertie [1] inthe USA. Originally commissioned for1440 MW and later uprated to 1600 MWat ±400 kV, its northern terminal is sitedin The Dalles, Oregon, and its southernterminal at Sylmar, in the northern tipof the Los Angeles basin. This projectwas undertaken together with GeneralElectric, and started operating in 1970.In all, the company installed eight mercury-arcvalve based HVDC systemsfor a total power rating of 3400 MW.Although many of these projects havesince been replaced or upgraded withthyristor valves, some are still in operationtoday, after 30 to 35 years ofservice!Mercury-arc valves in the first Gotland link,1954The semiconductor ‘takeover’ beginsMercury-arc valve based HVDC hadcome a long way in a short time, but itwas a technology that still harboredsome weaknesses. One was the difficultyin predicting the behavior of thevalves themselves. As they could notalways absorb the reverse voltage, arcbacksoccurred. Also, mercury-arcvalves require regular maintenance,during which absolute cleanliness iscritical. A valve that avoided thesedrawbacks was needed.The invention of the thyristor in 1957had presented industry with a host ofnew opportunities, and HVDC transmissionwas soon seen as a promising areaEarly HVDC projectsThe early 1950s also saw the British andFrench power administrations planninga power transmission link across theEnglish Channel. High-voltage DCtransmission was chosen, and the companywon its second HVDC order – thistime a link for 160 MW.The success of these early projects generatedconsiderable worldwide interest.Gotland 1 extension, with the world’s first HVDC thyristor valvesSpecial ReportABB Review63

of application. As part of its activities inthe semiconductor field, the companyhad continued to work at developinghigh-voltage thyristor valves as an alternativeto the mercury-arc type. In thespring of 1967, one of the mercury-arcvalves used in the Gotland HVDC linkwas replaced with a thyristor valve. Itwas the first time anywhere that thiskind of valve had been taken into commercialoperation for HVDC transmission.After a trial of just one year, theSwedish State Power Board ordered acomplete thyristor valve group for eachconverter station, at the same time increasingthe transmission capacity by50 percent.Around the same time, tests were carriedout on the Gotland submarine cable,which had been operating withoutany problems at 100 kV, to see if itsvoltage could be increased to 150 kV –the level needed to transmit the higherpower. The tests showed that it could,and this cable was subsequently operatedat an electrical stress of 28 kV/mm,which is still the worldwide benchmarkfor large HVDC cable projects today.The new valve groups were connectedin series with the two existing mercuryarcvalve groups, thereby increasingthe transmission voltage from 100 to150 kV. This higher-rated system wastaken into service in the spring of 1970– another world’s ‘first’ for the Gotlandtransmission link.With the advent of thyristor valves itbecame possible to simplify the converterstations, and semiconductors havebeen used in all subsequent HVDClinks. Other companies now began toenter thefield.BrownBoveri(BBC) –which latermergedwith ASEAto formABB – teamed up with Siemens andAEG in the mid-1970s to build the1920-MW Cahora Bassa HVDC linkbetween Mozambique and South Africa.The same group then went on to buildthe 2000-MW Nelson River 2 link inCanada. This was the first project toemploy water-cooled HVDC valves.The late 1970s also saw the completionof new projects. These were the Skagerraklink between Norway and Denmark,Inga-Shaba in the Congo, and the CUProject in the USA.The Pacific Intertie was also extendedtwice in the 1980s, each time with thyristorconverters, to raise its capacity to3100 MW at ±500 kV. (ABB is currentlyupgrading the Sylmar terminal by replacingthe converters and control system.)Itaipu – the new benchmarkThe contract for the largest of all HVDCtransmission schemes to date, the6300-MW Itaipu HVDC link in Brazil,was awarded to the ASEA-PROMONconsortiumThe scale and complexity of theItaipu project presented a considerablechallenge, and it can beconsidered as the start of themodern HVDC era.in 1979.This projectwas completedandput intooperation inseveralstages between1984 and 1987. It plays a key rolein the Brazilian power scheme, supplyinga large portion of the electricity forthe city of São Paulo.The scale and technical complexity ofthe Itaipu project presented a considerablechallenge, and it can be consideredas the start of the modern HVDC era.The experience gained in the course ofits completion has been in no small wayresponsible for the many HVDC ordersawarded to ABB in the years since.After Itaipu, the most challenging HVDCproject was undoubtedly the 2000-MWQuébec – New England link. This wasthe first large multi-terminal HVDCtransmission system to be built anywherein the world.HVDC cables have kept paceAs the converter station ratings increased,so too did the powers and voltagelevels for which the HVDC cableshad to be built.The most powerful HVDC submarinecables to date are rated 600 MW at450 kV. The longest of these are the230-km cable for the Baltic Cable linkbetween Sweden and Germany, andthe 260-km cable for the SwePol linkbetween Sweden and Poland.Foz do Iguaçu converter station with the Itaipu 12,600-MW power station in the backgroundHVDC todayThe majority of HVDC converter stationsbuilt today are still based on the principlesthat made the original Gotland linksuch a success back in 1954. Station de-64Special ReportABB Review

sign underwent its first big change withthe introduction of thyristor valves inthe early 1970s. The first of these wereair-cooled and designed for indoor use,but soon outdoor oil-cooled, oil-insulatedvalves were also being used. Today,all HVDC valves are water-cooled [2].Good examples of modern bulk powerHVDC transmission are the links ABB isinstalling for the Three Gorges hydroelectricpower plant project in China.(See article starting on page 6.)In 1995 ABB presented a new generationof HVDC converter stations: ‘HVDC2000’ [3]. HVDC 2000 was developedto meet stricter electrical disturbancerequirements, to provide better dynamicstability where there was insufficientshort-circuit capacity, to overcomespace limitations, and to shorten deliverytimes.A key feature of HVDC 2000 was theintroduction of capacitor commutatedconverters (CCC). This was, in fact, thefirst fundamental change to have beenmade to the basic HVDC system technologysince 1954!HVDC 2000 also includes other ABB innovations,such as continuously tunedAC filters (ConTune), active DC filters,outdoor air-insulated HVDC valves, andthe fully digital MACH2 control system.Submarine cable for the 600-MW BalticCable HVDC link between Germany andSwedenBaltic Cable HVDC converter stationThe first project to employ HVDC 2000with CCC and outdoor valves was theGarabi 2200-MW HVDC back-to-backstation in the Brazil – Argentina HVDCInterconnection.HVDC Light TMHVDC technology has become a maturetechnology over the past 50 years andreliably transmits power over long distanceswith very low losses. This begsthe question: where is developmentwork likely to go in the future?It was conceived that HVDC developmentcould, once again, take its cuefrom industrial drives. Here, thyristorswere replaced a long time ago by voltagesource converters (VSC), with semiconductorsthat can be switched off aswell as on. These have brought manyadvantages to the control of industrialdrive systems and it was realized thatthey could also apply to transmissionsystems. Adapting the technology of voltagesource converters to HVDC, however,is no easy matter. The entire technologyhas to change, not just the valves.As development of its VSC converter gotunder way, ABB realized that the insulatedgate bipolar transistor, or IGBT,held more promise than all the otheravailable semiconductor components.Above all else, the IGBT needs onlyvery little power for its control, makingseries connection possible. However, forHVDC a large number of IGBTs wouldhave to be connected in series, somethingindustrial drives do not need.In 1994, ABB concentrated its developmentwork on VSC converters in a projectthat aimed at putting two convertersbased on IGBTs into operation forsmall-scale HVDC.An existing 10-km-long AC line in centralSweden was made available for theproject.At the end of 1996, after comprehensivesynthetic tests, the equipment was installedin the field for testing under serviceconditions. In 1997 the world’s firstVSC HVDC transmission system, HVDCLight [4], began transmitting powerbetween Hellsjön and Grängesberg inSweden.In the meantime, seven such systemshave been ordered, and six of them arenow in commercial operation in Sweden,Denmark, the USA and Australia.HVDC Light is now available for ratingsup to 350 MW, ±150 kV.ABB is to date the only company thathas managed to develop and build VSCHVDC transmission systems [5].Special ReportABB Review65

Shoreham station, 330-MW HVDC Light TM Cross Sound Cable link, USAHVDC Light land cableOne advantage of HVDC Light is that itallows an improvement in the stabilityand reactive power control at each endof the network. Also, it can operate atvery low short-circuit power levels andeven has blackstartcapability.The HVDCLight cable ismade of polymericmaterialand is thereforevery strong androbust. Thismakes it possibleto use HVDC cables where adverselaying conditions might otherwise causedamage. Extruded cable has also madevery long HVDC cable transmission onland now economically viable. An exampleis the 180-km-long HVDC Lightinterconnection ‘Murraylink’ in Australia.And the next 50 years?HVDC transmission has come a longway since that first Gotland link. Butwhat does the future hold for it?Bulk transmission is likely to rely onthyristor-based technology for manyyears sinceit is reliableThe introduction of capacitorcommutated converters wasthe first fundamental changemade to the basic HVDCtechnology since 1954!and low incost, pluslosses arelow. Increasingthe voltageis oneway to gohere as it would allow much higherpowers and very long distances forthe links.HVDC Light has the potential to bedeveloped further. One direction mightbe toward higher voltages and powers,but low power and relatively high voltagesare also conceivable for systemsfor smaller loads and generators.The development of HVDC Light cablehas made it possible to link up networksacross very deep waters that have previouslymade such schemes unthinkable.The most interesting prospects forHVDC Light, however, lie in its potentialfor building multi-terminal systems. Inthe long term it might offer a genuinealternative to AC transmission, whichtoday completely dominates this sector.Gunnar AsplundLennart CarlssonABB Power TechnologiesLudvika/Swedengunnar.asplund@se.abb.comlennart.k.carlsson@se.abb.comOve TollerzABB Power TechnologiesKarlskrona/Swedenove.tollerz@se.abb.comReferences[1] L. Engström: More power with HVDC to Los Angeles. ABB Review 1/88, 3–10.[2] B. Sheng, H. O. Bjarma: Proof of performance – a synthetic test circuit for verifying HVDC thyristor valve design. ABB Review 3/2003, 25–29.[3] B. Aernlöv: HVDC 2000 – a new generation of high-voltage DC converter stations. ABB Review 3/1996, 10–17.[4] G. Asplund, et al: HVDC Light – DC transmission based on voltage sourced converters. ABB Review 1/1998, 4–9.[5] T. Nestli, et al: Powering Troll with new technology. ABB Review 2/2003, 15–19.Further information on HVDC can be found at www.abb.com/hvdc66Special ReportABB Review

ABB ReviewSpecial ReportPower TechnologiesEditorial boardMarkus BayeganGroup R&D and TechnologyGeorg SchettABB Power TechnologiesKlaus TreichelABB Power TechnologiesNils LefflerChief Editor, ABB ReviewPublisher and copyright © 2003ABB LtdZurich/SwitzerlandPublisher’s officeABB Schweiz AGCorporate ResearchABB Review / RD.REVCH-5405 Baden-Dättwilabbreview.abbzh@ch.abb.comPrintersVorarlberger Verlagsanstalt AGAT-6850 Dornbirn/AustriaDesignDAVILLA Werbeagentur GmbHAT-6900 Bregenz/AustriaPartial reprints or reproductions are permittedsubject to full acknowledgement.Complete reprints require the publisher’swritten consent.ISSN: 1013-3119www.abb.com/abbreviewSpecial ReportABB Review67

Don’t let your city lose its shine.Think of all the ideas you put on paper.In China,that’s a lot of paper.That’s why we helped Asia Pulp and Paperbuild the fastest mill in the world.ABBalso created a new generation of integratedautomation that can monitor and operatethe entire plant from a single screen. At ABB,we believe the most important thingwe build today is knowledge. Because thepower that will drive the next hundred©ABB 2003years is the power of ideas.Proven power technologiesintegrated in record timew w w . a b b . c o mABB’s cutting edge technologies for grid reliability include HVDCand FACTS: High Voltage Direct Current (HVDC) technology byABB has built-in overload control and can be loaded fully withoutincreasing the risk of cascaded line tripping. Our Flexible ACTransmission Systems (FACTS) allow more power to flow on existinglines with minimum impact on the environment, substantiallyshorter project implementation times, and this at lower costs.Contact the worldwide market leader in power technologies:www.abb.com/poweroutagea