___________________________________ JICABLE '99

A1.6Construction of long distance 500 kV XLPE cable lineOHATA K, T5UCHIYA 5., Tokyo Electric Power Co. Ltd., Tokyo, Japan

5HINAGAWA N., The Furukawa Electric Co. Ltd., Tokyo, Japan

FUKUNAGA 5., 5umitomo Electric Industries Ltd., Tokyo, Japan

OSOZAWA K., Hitachi Cable Ltd, Tokyo, Japan

YAMANOUCHI H., Fujikura Ltd., Tokyo, Japan

RésuméAu terme de 5 années d'études de développement,

Tokyo Electric Power Co.,(TEPCO) a appliqué descâbles isolés XLPE de 500kV ayant une épaisseurd'isolation de 27mm et des joints moulés à extrusion(EMJs) aux lignes réelles sur une longueur de40km(2cct), dont 120 EMJs/cct,actuellement enconstruction par 4 fabricants de câbles. Afin d'assurerla fiabilité des câbles et des EMJs, nous utilisons unetechnologie récemment mise au point et d'une hauteprécision. Elle comporte notamment des équipementsd'inspection toute résine en usine/sur site et deséquipements d'inspection à rayon X et microfocus.Une fois que tous les EMJs seront installés,des essaisde décharge partielle seront effectués afin de vériefierleur état et ils seront placés en utilisationcommerciale en l'an 2000.

1. IntroductionWhile 275 kV underground transmission lines are

chiefly used to supply electric power tooverpopulated Tokyo, the increase of energydemand in recent years necessitated 500kVunderground transmission lines to supply muchmore electric power directly into the central area ofthe metropolis. Conventionally, oil-filled cableswith semi-synthetic paper insulation have beenpractically used for long-distance 500kV powercables. This time, the authors have developed,considering the expanding applications of cross­linked polyethylene insulated (XLPE) cablesbecause of freedom from oil tanks and ease ofmaintenance, a 500kV XLPE cable and anintermediate joint, based not only on the drasticimprovements in the quality control of XLPE cablemanufacturing but also on the service record of 275kV class lines.Actual applications of 500kV XLPE cables were

limited until now to the connection lines within thepremises of hydroelectric power stations, havingan insulation thickness of 32 mm withoutintermediate joints [1]. In order to realize asmaller-sized cable and an intermediate joint, 2.5years offundamental studies as well as 1.5 years ofdevelopmental studies were carried out, followedby about one year of long-term verification tests

AbstractAfter 5 years of developmental studies, Tokyo

Electric Power Co., (TEPCO) has applied 500kVXLPE insulated cables with insulation thickness of27 mm and extrusion molded joints (EMJs) to theactual line with the length of approx. 40km(2cct)including 120 EMJs/cct , which is presently underconstruction by 4 cable manufacturers. In order toassure the reliability of cable and EMJs, newlydeveloped and highly accurate inspectiontechnology --including .in-fàctory / on-site all resininspection equipment, microfocused X-rayinspection equipment and so on-- has beenemployed. After installation of all EMJs, partialdischarge tests will be carried out to verify theirsoundness and to be in commercial use in 2000.

aimed at verifying overall reliability including thecable installation technology [2][3][4][5][6]. Thecable insulation .thickness was decided to be 27mm, the same as for conventional 275 kV XLPEcables, based on the studies on the breakdownstress and .its thickness dependence in addition tothe characteristics of outer semi-conductive layerstreated portion at joints. Meanwhile aninvestigation of various intermediate jointsresulted in the adoption of the extrusion' moldedjoint (EMJ) type, which are compact and highlyreliable and have much service record in 275kVlines.With the strength of this successful development,TEPCO has applied the 500kV XLPE cable andEMJ to the Shin-Keiyo-Toyosu line, andconstruction is proceeding satisfactorily. Thispaper reports on the design, quality control,installation, and jointing work of the Shin-Keiyo­Toyosu line.

2. Construction of Shin-Keiyo '1byosu LineThe Shin-Keiyo-Toyosu line is the world's firstlong-distance underground line of 500kV XLPEcable with a length of approx. 40 km by 2 circuits,which supplies a large amount of electric powerdirectly into the Shin-Toyosu substation in thecentral part of the metropolis from the Shin-Keiyo

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substation, a major substation in the outer500kVpower grid system. (See Fig-I)The outline of the transmission line is as follows,1) Name ofline : Shin-Keiyo-Toyosu line2) Nominal voltage: 500kV3) Number of circuit: 2(3 In the future)4) Sector: From Shin-Keiyo substation to Shin-Toyosu substation

5) Route length : 39.8 km6) Cable: XLPE cable, 2500 mm 2(Single Core)7) Number of Accessories per phase: 40 EMJs

and 2 Gas-immersed sealing ends8) Transmission capacity : 900 MW/cet

(1200 MW/cet in the future)9) Start of commercial use :Scheduled in

November, 2000

3. Cable Design and Quality Control3.1 Cable DesignRequired insulation thickness The required cableinsulation thickness was obtained by the equationsbelow,VAC , the design withstand voltage at commercial

frequency is,VAC= 5501""3'KI'K2'Ka = 970 kV

where, KI: degradation coefficient = 2.3 (when 30years are converted into 1 hr using the

15-th power law)K 2 : temperature coefficient = 1.2Ka: coefficient of uncertainty = 1.1

Vimpr the design withstand voltage againstlightning impulse is,Vimp = LIWV (=1425 kV)'KI'K2'Ka = 1960 kV

where, KI: degradation coefficient for repeatedloading = 1.0

K 2 : temperature .coefficient = 1.25Ka: coefficient of uncertainty = 1.1

From these, the required insulation thickness t iscalculated as,

t = Max [VAC IEL(AC), VIMPIEL(IMP)]= Max [24.3, 24.5] -+ 25 mm where,

EL(AC) : minimum breakdown strength in 1 hr value= 40 kY/mmEL(lMp}: minimum breakdown strength = 80 kY/mmFurther consideration was given as to insulationcoordination with joints, in which jointcharacteristics are known to be influenced by theperformance of the outer semiconductor treatedportion, and the insulation thickness wasultimately decided to be 27 mm.Cable structure The cable was designed to havesuch a structure that the required insulationthickness mentioned above coincides with the localminimum value. Table i gives the cable structure.Cable specifications Based on the developmentalstudies, specifications for cable performance weredetermined as foilows.(a) AC and lightning impulse withstand voltagetests

275kV Underground Transmission Line

Fig-1 Cable route of Shin-keiyo-Toyosu Line

Table-1 Structure of 500kV XLPE Insulated CableItem Unit Specification

Nominal Voltage kV 500Number of Conductor - 1

Nominal Cross-2500sectional Area

ConductorShape .Sectional and compacted

Outer Diameter mm 61.2Inner semiconductive layer Approx.

2.5thickness mmInsulation thickness mm 27.0

Outer diameter of insulation mm 102.0Outer semiconductive layer Approx.

1.0thickness mmThickness of cushion layer and Approx.

3.5shield layer mmAluminum sheath thickness mm 3.3

Anti-corrosion layer thickness mm 6.0Max. outer diameter mm 170

Approx. weight Approx. 43.5ka/m

Max. DC conductor Q/km 0.00746resistance(20"C )Min. insulation resistance(RT) MQ'km 3,000

Cable capacitance IlF/km 0.23

While the design withstand voltage was used forthe AC test, positive and negative polarities wereused in the lightning impulse tests consideringthat many lightning strikes with positive polarityare seen in winter.(b) Shippingwithstand voltage testThe test is intended, incorporating partialdischarge test, to confirm that the cablewithstands an over-voltage that can occur in the500kV power grid system, as weil as to detecthuman errors such as external defects. The testvoltage is calculated as foilows.

V = Vo X Cl x C2::::;:465 kVwhere, Vo: max. voltage on cable = 550 kV

Cl : multiplication coefficient forwithstand voltage test = k, x k2 X ka

C2 : temperature coefficient = 1.2k, : time conversion coefficient = 0.61 (to convertthe total duration time of the lasting and pulsatingover-voltages that appear in the power grid systeminto 10 min, namely, the duration of shipping

1

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Fig-2 Breakdown Characteristics of ExternalDamages for Cable

d.001 0.01 0.1 1 10 100 100010000

Time to breakdown [Hours]

withstand voltage test. A life index of n = 15 hasbeen applied)k2 : voltage multiple coefficient for load shut-off =1.65/1""3k3 : allowance for withstand voltageMeanwhile, the duration time of test was decidedaccording to the breakdown characteristics ofexternal defects shown in Figure 2, whichindicates that a loading time of 15 min is necessaryfor a test voltage of 465 kV.Major cable specifications are shown in Table 2.3.2· Quality CQntrQI of Cable ManufacturingIn the quality control of 500kV XLPE cablemanufacturing, it is of the utmost importance tocontrol the permissible defects shown in Table 2.

Table-3 Quality Control Method for ForeignP rti 1 . C bl M uf t P

Among these, voids can be maintained well belowthe permissible level by controlling thetemperature and pressure at the cross-linkingprocess, and semi-conductive protrusions by athree-Iayer simultaneous common extrusion of theultra-smooth semi-conductive material,respectively. Furthermore, foreign particles aremaintained below the permissible level byapplication of quality control measures given inTable 3.

4. Design and QuaJity Control of EMJ4.1 Design QfEMJ Required insulatiQn thicknessThickness of MQlded Insulation[ tEMJ:In order ta provide the same design withstandvoltage as the cable --VAC and VIMP- - ' the designstresses of the EMJ were derived as: EL,EMJ(AC) = 27kVlmm; EL,EMJ(IMP) =60 kVlmm; and, were used tocalculate the required insulation thickness tEMJ •

tEMJ =Max [VACIEL,EMJ(AC), V~L,E:MJ(IMP)] =Max [36,33]-+36 mmThickness QfQuter cQnductor treated portion. t~

A cable structure of the largest conductor size2500 mm2

"- , in which the stress at the outerconductor treated portion becomes thegreatest,was used for design. Using the insulator insidediameter of 61.2 mm, the required insulatorthickness for the design withstand voltages arecalculated by the following equation:V / (61.2 + 2tc) / 2 / log «61.2 + 2tc) / 61.2) = EL.CBy substituting the minimum breakdown stressesat the outer conductor treated portion, EL.C(AC) =

a IC es ln a e an ac urmg rocessProcess Control target Control measure

Insulation No admission Material is transported usingmaterial exclusive tank trucks from

acceptance resin supplier, is accepted in asuper-clean booth prepared ina materialacceptance room.

No Sampling test of materialcontamination pelletis carried out.

Material No admission Air pressure transfer in atransfer hermeticallv sealed duct

Noadmission Dust is exclude by applicationofultra-fine mesh screen.

Mixingof Noadmission Controlled by the opening ofadditive screen mesh

Preparatio Noadmission Cross-head assembly in an of cleanness-controlled extruder

extrusion roomInsulation Noadmission Controlled by the opening ofextrusion screen meshïsame as for

mixing ofadditive)No An optical window section is

contamination provided in extruder's resinchannel just in front ofcrosshead, in which the entiremolten resin for insulation ismonitored using laseand CCDcamera.(Detection sensitivity :50 IJ. m)

Product No Sliced samples ofinsulator areinspection contamination taken for inspection from both

endsofextruded cable.

o :Defects of Inserted needle

o :Oefects of needle hole

f 500kV XLPE C blT bl 2 S ifia e- snec cations 0 a eItem Specification

Conductor resistance Below the value in Table-lCablecanacitance Same as above

Insulation resistance DittoACwithstand voltage 465kVl5min

Partial discharge Not detected at 465kV

= Sensitivity: <5pC0 Temperature Below 0.05%'.;jC<$ dependency of tan t5 At 320kV(RT. 60,90, 105~)-.,rn RT 970kVlhr= AC withstand voltage......

90~ 805kVlhrl'il

~ Lightning impulse RT ± 1960kV3shotsX withstand voltage 90"e ± l560kV3shots

Void <20/.1.m

particlelMetal <50/.1.m

Fibrous <1000/.1.mProtrusion <50/.1.m

>lOMQ'km...,

Insulation resistance NormalPVCQ)

~ >lMQ'kmoC<$

Flame retardant PVC......0 DC withstand voltage -25kVlmin:>l:l. Lightning Imp.

Withstand voltage -90kV3shots

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Heat hase

Fig-3 Structure of EMJ

Extrusion wald

~ ._. _ _ . _ - - - _ ImaceruEfhCCD...f..+ P~SSIDC~ 1 unit

iSl()o,W"-'~ $~­

S w-.-.r..__ .Ea-y~~

a> 0- O s.-iII__~ 0 - ....

AlI resTri'inJJpectioQ system

Observation window "==T==='=: :~ Elltl'uder(Grass tube included )

4 2 EMJ Installation TechnologyQuality control at installation site is an essentialtech nology to assure an insula tion performancethat has been designed. Since the performance ofEMJ is governed by foreign particles andprotrusions of the ILm orders, it is of the utmostimportance to qual ity control these defects. Inpa rticular for 500kV EMJs. which have much moreseve re allowances than 275kV EMJ s in te rms ofdetrime ntal inclusions . it is essential to implementa close quality control as weil as to introduce newins pect ion technologies.Table 4 shows control levels of defects and Table 5provides quality control methodologies classifiedby targets, respectively.

27.6 kY/mm and EL.COMP) = 57.5 kY/mm. th erequired insulation thickness tc is calculated as:te = Max [tC(AC)' te(ThlP)) = Max [27. 26]-27 mmGiving the sa me value as for the cable shown inSectio n 3-1 (1). Figure 3 shows the structure ofEMJ.

Fig-5 Inspection usin g Micro-Focus X-rayInspection System

Fig-4 Inspection usin g the AlI Extrusion ResinInspection System

Table 4 Defect Control Levels of EMJ

Adoption of cIeanness upgrading techoologyIn the EMJ jointing work , clean rooms have beenset up on site to cope with the str ict permissibl elevel for foreign particles in the order of ILms.Auxiliary rooms are provided at both ends of theciean room to eliminate ad verse influences due toentry of workers and equipment as much aspossibl e; intermediate partition wall s are providedin th e clean room; and the cleanness of equipmentis upgraded. Through these measures, the cleanlevel is maintained below the class 50 thousand.

-Typeof Defect Control Leve!

Void Spherica! Void <l>25/l mForeign particles Meta! ieo« m

orProtrusion Cotton Fiber 2mm

Table-ô Quality Control MethodologiesClassified by Targets

• N• ........- Noc......1:ioa NoCoa~_bOg....... C\eaaDoo......1_troI ..-..... AlI ...... ___

F.....,(Il P~ (CIo_""" Cbai.". ,II1k'J'. otte. M.icro-~x-...,

FibrlNa Cle...........I"""r;rot ElU:uooaooo. ofFonip"~" (ct... $0000) 1l0 U Oli liber fntm. dOlha

AlI__

Col:_Fib.r","""of

'ttruaioa ...4 aou-li..D..kI.DcSpbencal VOId - coDditi~ -

(U'C.hadiAl telldu~·b&...t

=~"E1tel'll&1 D"rtoCl - CoDtrolof

PIU1l.I.l dUclIarc-"'teiluu.ll.tioll l'OCtduteaControlo!

.nt'U*iOD and.O'OM-llll.kiIlrPec:uliuVoid - colldi tio ll8 Pamal<Wo:.barw- tell

(illC.h.diIo~~~~IIC7.b..ed

Ail e xtrusion re s in in spect ion s ystemAn inspection system comprised of optical systemand image processing unit has been developed tomonitor ail the extrusio n resin , taking advantageof the transparency of molten polyethyle ne beingextruded . The inspection system is capable of on­line monitoring foreign particles in the res induring extrusion. thus verifying that no defectsexist in the EMJ molded insula tion . The systemconsists of an optical system of either transm issionor reflection type. an imaging deviee of CCDcamera. and a light source of either visible light orlaser. What is more. the sys te m is transportable.allowing easy assembly in the clean room on site .Figure 4 shows the inspection syste m in operation.Mjcro.focused X-ray inspectjon technQlo~

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EMJs undergo Xvray inspection. after cross-linkingprocess, for the interior insulator in order to detectharmful foreign particles that might have beencontained by any chance. A miero-focus Xvrayinspection system (focus size: 10 - 50 /1 m) wasintroduced in place of a small-focus X-rayinspection system (focus size: 200/1 m) used for 275kV EMJ so as ta obtain clear images with highmagnification, enabling detection of minute foreignparticles exceeding the permissible level.Furthermore, aiming at reducing the X-rayinspection time, X-ray film as imaging medium hasbeen replaced by imaging plate «an electronicdevice--. and an image recognition systemincorporating image processing unit and computerwas introduced ta implement automatic judgementof detrimental foreign particles.Figure 5 shows the micro-focus X-ray inspectionsystem in operation.High precisioD partjal discharge detectioD

technol0eYPartial discharge test is effective in screeningEMJs for defects, since ail defeets in EMJ areconcerned with this diseharge phenomenon duringtheir course ta breakdown. While detrimentaldefects such as foreign particles, protrusions, andvoids can be eliminated by means of quality controland inspection during installation, external defectsand interfacial defeets --which unexpectedlydevelop at the interface within the joint-- aredifficult to be detected by these méans, thusrequiring a partial discharge test ta confirm EMJ'sintegrity after assembly.Test conditions fQr partial djscbarie Testconditions for partial discharge measurement haveta be determined according ta the partial dischargecharacteristics of the external and interfacialdefects --the objectives ta which the test isintended for-o . which are ta be obtained by carefulinvestigation. Definite conditions are underexamination sa as ta make the test effective indeteeting those defeets that become detrimentalwhen the line is exposed to over-voltages such assurges.Partial discbarge measurement system

A partial diseharge measurement method usingfoil electrodes. which proved itselfin 275 kV lines,has been adopted as measurement method. In thismethod, discharge signaIs are picked up by metalelectrodes attached on the anti-corrosion layers onboth ends of the insulating tube at the insulatingjoint, are tune-amplified in a less noisy high­frequeney band (several ta several tens of MHz) saas to detect partial discharge.Conventionally, because normal joints have noinsulating flange, it was unable ta detect partialdiseharge direetly at an intended joint, andtherefore, measurement used ta be carried outfrom a neighboring joint indirectly. This resulted in

2300

Lead win

<'

P!l 1111

Fig-ê Normal Joint Adapted for Insulating Joint

a less accurate measurement compared withinsulating joints. Accordingly, a normal joint thatenables direct partial discharge measurement --tobe called " normal joint adapted for insulatingjoint"-- has been developed. The structure of thisjoint is shown in Figure 6. in which the joint isseen : to function, thanks to a lead wireincorporating a high-frequeney iron core. as anormal joint in the commercial frequency, and asan insulating joint in the frequeney band of partialdischarge measurement, thus permitting a high­precision partial diseharge measurement at thisjoint.Partial discharge tests are seheduled to be carriedout starting from May, 2000.

5 !&ne:Cable Lavine: TecbnoloeYIn actual line construction. cable transportationmethod ta the site and cable laying method on siteare two major technological tasks. A long cablelaying technique has been developed and appliedto the Shin-Keiyo-Toyosu line sa as ta reduce theterm of construction as weil as costs. Its outline ispresented below.Cable transier metbod in tunnel using CarrierIn ordinary land transportation using cable drums.the length of cable is limited ta around 550 m dueto weight restrictions. In the case of the Shin­Keiyo-Toyosu line, the route runs partly along theshoreline of Tokyo-Bay, and its last 15 km to theShin-Keiyo substation lie entirely in a tunnel.Taking these advantages, a cable transfer methodhas been developed ta laying Long-Length cable, inwhich Long-Length cable is shipped by sea lay itdirectly to the tunnel from the landing point. Inthe tunnel. it is transferred using the Carriers.The driving system for the Carrier classified twotypes: "Twin pulley system" and "Magnetic beltsystem".Figure 7 shows schematics of the Carrier. The twinpulley system uses a pair of pulleys (rotating dise).which holds by rotating a conneeting pipe on thebottam of the carrier to push it forward; while themagnetic belt system uses a permanent magnetbelt installed on angle structure in the tunnel,which by rotating attraets L-shaped steel strips onthe bottom of the carrier ta push it forward.The magnetic belt system was used in windingtransfer sectors for its adaptability to curvatures ofsmall radius, while the twin pulley system wasused for rather straight sectors for cost reductionmerits. Due ta the adoption of the Carrier, it was

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possible to lay cable len gth of 1800 m at a speedfaster than the conventional method by as much asfour to live times , without giving excess ive forcesonto the cable.Trayerse cable pay-out methodOn the Shin-Toyosu substa tion side, the cabletrans fer method mentioned above was unavailabl esince the route, although it faced the sea, includedduct secto rs . Therefore, permission was obtainedfrom the road administrator for special vehicles(traile r for transportation of lateral cable drums)to pass only specilied sections of short distance,and a feeding method for long cables using atraverse pay-out was developed as described below.A lateral cable drum on which a long cable iswound has a width of 9.0, more than twice as wideas 3.6m of longitudinal drums. This makes itutterly impossible to feed the cable within a timepermitted for dedica ted use of road, since the worknecessitates a large worki ng area, occupies th eentire road forcing traffic suspension, takes a longtime for drum arrangements and so forth. Atraver se pay-out method was ther efore developed,which enabled assembly of temporaryarrangements in a short tim e avoiding trafficsus pension, thus bein g capa ble of cable feedingwithin a time permitted.The method uses a bender that can give the cable ahorizontal 90 · bend without over-force, whichmoves in the direction of cable feed in accordancewith the position of cable pay-off traversing thecable drum. Figure 8 shows the feeding of cableusing the traver se pay-out method. The methodenabled cable feeding of 1200 m max . which ismore than twice th e length in the conve ntiona lmethod.

Fig-8

6 ConclusionA 500kV XLPE cable and an EMJ were developedto realize a 500kV long-distance cable line , andhave been applied for the Shin-Keiyo-Toyosu line ,which is now under construction. Majordevelopme nt subj ects includes: identification ofperform ance governing factors, establishment ofqua lity control technology for these facto rs , andestablishme nt of install ation technology.After ail EMJsare installed , partial dischargetests will be carr ied out to verify th eir soundness,and the lin e will be in commercial use in 2000 .The tec hnologies applied to the Shin-Keiyo-Toyosuline incl uding those of quality control formanufacturing of long cables, installation, qualitycontrol for EMJ jointing , and partial discharge testare thought to be top level of the world , andcontr ibuting significantly to the development ofextra high-voltage extruded insulation cabletechnology.

Reference s[1]K. Ogawa , et al., "The World's Firs t Use of500kV XLPE Insula ted Aluminum SheathedPower Cables at the Shimogo and Im aichi powerstations", IEEE 1989 SM 643-8 PWRD[2]T. Kubota et al., "Deve lopment of500kV XLPECables and Accessories for Long DistanceUnderground Transmission Line - Part 1:Insul ation Design of Cabl es", IEEE Trans. OnPower Delivery, Vol.9, No.4, Oct . 1994[3] T. Kubota et al., "Same title as ref. [2] - Part 2:Join ting Techniques", IEEE Trans. On PowerDelivery, Vol.9, No.4, Oct . 1994[4]M. Fukawa et al., "Same title as ref. [2]- Part 3Electrical Properties of 500kV XLPE Cables",IEEE Trans. On Power Delivery[5]N, Takeda et al., "Same title as ref. [2] - Part 4Electrical Properties of 500kV Extrusion MoldedJ oints", IEEE Trans . On Power Delivery[6]K. Kam inaga et al., "Same title as ref. [2] - Part5 Long-Terra Perform ance for500kV XLPE Cablesand J oints", IEEE Trans . On Power Delivery

/Rail

Hauling machineCable Connecting pipe

Twin pully

Twin pulley driving unit Caree r

(1)Twin Pulley System

Hauling machine L-shaped steel stripCable

\Magnetic belt driving unit

(2)Magne tic Belt SystemFig-7 Career system for cable transfer in tunnel

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