ABB Review Special Report - ABB - ABB Group

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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
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Contents61319252932374247HVDC super
Page 4 and 5: ForewordReliable grids, with power
Page 6 and 7: HVDC superhighwaysfor ChinaLeif Eng
Page 8 and 9: new regional networks. A national i
Page 10 and 11: Power ratingsThe links are designed
Page 12 and 13: Power take-offElectric power genera
Page 14 and 15: 1The Dafang 500-kV series capacitor
Page 16 and 17: 41.51.00.50-0.5-1.0-1.55002500-250-
Page 18 and 19: 8400 kVCircuit of dynamic load bala
Page 20 and 21: While construction of the new lineh
Page 22 and 23: V (pu)61.61.41.21.00.80.60.40.20V/I
Page 24 and 25: 8SVC performance. Results of a phas
Page 26 and 27: 1TEC receives the information it ne
Page 28 and 29: 5TEC electronics - tried and tested
Page 30 and 31: the past. An increasing number of c
Page 32 and 33: The big pictureDetecting power syst
Page 34 and 35: highly accurate system overview. Se
Page 36 and 37: 2Example of graphical user interfac
Page 38 and 39: 111010090807060petitive. This has r
Page 40 and 41: 4independent applications without r
Page 42 and 43: Cold storageThe battery energy stor
Page 44 and 45: 2Battery module, comprising 10 cell
Page 46 and 47: Reactive power [pu]Inductive Capaci
Page 48 and 49: CR13025201510501986 1988 1990 1992
Page 50 and 51: and the system as a whole will stil
Page 52 and 53: EnvironmentGrid securityEconomyOper
Page 56 and 57: 3HVDC Light extrudedsubmarine cable
Page 58 and 59: 1KarlshamnBornholmBaltic SeaSwePol
Page 60 and 61: Metal objects on Swedish coast that
Page 62 and 63: The problem was solved in 1929 by a
Page 64 and 65: of application. As part of its acti
Page 66 and 67: Shoreham station, 330-MW HVDC Light
Page 68: Don’t let your city lose its shin
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ABB Review Special Report - ABB - ABB Group

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