ABB Review Special Report - ABB - ABB Group

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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
Page 2 and 3: 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 50 and 51: and the system as a whole will stil
Page 52 and 53: EnvironmentGrid securityEconomyOper
Page 54 and 55: On most offshore installations, the
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

ABB Review Special Report - ABB - ABB Group

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