mechanical and electrical performance of polypropylene paper laminates versus cellulose paper for...

8/12/2019 MECHANICAL AND ELECTRICAL PERFORMANCE OF POLYPROPYLENE PAPER LAMINATES VERSUS CELLULOSE PAPER

1/6

Conference Record of the 1992 IEEE Internat ional Symposium on Electrical Insulation, Baltimore, M D USA J u n e 7-10 1992

MECHANICAL AND ELECTRICAL PERFORMANCE OF POLYPROPYLENE PAPERLAMINATES VERSUS CELLULOSE PAPER FOR POWER CABLESDan R. Watson and John C. ChanAlcatel Canada Wire Inc.Toronto, Ontario, Canada.

ABSTRACTThi s paper pr esent s t he resul t s ofl aboratory eval uati on of pol ypr opyl ene paperLamnat es (PPL's) manufactured by J apanese,European and Nort h Amer i can Suppl i ers, andt hei r compar ati ve perf ormance agai nst t heconvent i onal cel l ul ose paper di el ectr i c. Thel amnat es were eval uat ed as t o thei rphysi cal propert i es, and t he mechani cal andel ectr i cal per f ormance of model cabl esconstr ucted f rom t hem Al l t hr ee l am nat eshad si m l ar l oss character i st i cs whi ch weresi gni f i cant l y l ower t han t hose of cel l ul osepaper. The i mpul se st r ength of t he J apaneseand/ or Eur opean l amnat es was appr oxi matel y20% hi gher t han t hat of cel l ul ose paper ,whereas t he Nort h Ameri can l amnateexhi bi t ed onl y 10%hi gher i mpul se st rengt h.The ef f ect of per f orat i ons on t he i mpul sest rengt h of t he l amnates was al soi nvest i gat ed, the i dea bei ng t hatperf orat i ons woul d i mprove dryi ng andi mpr egnat i on. Resul t s i ndi cat e t hatperf orati on geomet r y si gni f i cant l yi nf l uenced breakdown st r ength.1. I NTRODUCTI ONAs t r ansm ssi on vol t ages i ncrease, t hef easi bi l i t y of any under gr ound hi gh vol t agecabl e system i s l i mt ed by oper at i ng cost sassoci at ed w t h di el ectr i c l osses andinstallation/maintenance cost s. Thedi el ect r i c l osses of any hi gh vol t age syst emare pr opor t i onal t o t he di el ectr i c const ant ,t he di ssi pat i on f act or and t he squar e of t heoperat i ng vol t age. Power cabl e syst ems rat ed138 kV and above tr adi t i onal l y empl oy oi l -i mpr egnat ed cel l ul ose paper di el ect r i cs. I nl i ght of t hi s, pol ypr opyl ene paper l am nat es( PPL' s) , havi ng l ower di el ectr i c const antand di ssi pat i on f actor, of f er substant i aladvant ages over cel l ul ose paper, especi al l yat vol t ages rated 5 0 0 kV and above. Theseadvant ages i ncl ude l ower di el ect r i c l ossesand hi gher di el ectr i c br eakdown st r engt h( especi al l y i n terms of i mpul se) , perm t t i nghi gher operat i ng st r esses and hence reducedi nsul at i on wal l . Thi s al l ows t he oper at i ngvol t age of an exi st i ng convent i onal pi pe-t ype cabl e syst em t o be upgraded w t houtrepl aci ng t he carr i er pi pe. These advant agesmake a PPL hi gh vol t age cabl e veryatt ract i ve to a ut i l i ty.

I n the past , t he devel opment of a pi pe-t ypePPL cabl e has been i nhi bi t ed by t he hi ghcosts of PPL' s as a r esul t of cer t ai npr opr i et ary r i ghts or i mpor t cost s. Nort hAmeri can and Eur opean sources of PPL' s haverecentl y emerged and hence, t hi s st udy wasi ni t i ated.Thi s st udy consi st ed of t he eval uati on ofPPL' s manufactured by J apanese ( desi gnatedLamnat e A) , Nort h Ameri can ( Lamnat e B andEuropean (Lamnat e C) suppl i ers .Convent i onal cel l ul ose paper i nsul ati on wasused as t he cont r ol . The l amnates wereeval uat ed w t h r espect t o thei r physi cal andmechani cal pr opert i es and t he el ect r i calperf ormance (l oss char acteri st i cs andi mpul se breakdown st rength) of model cabl esconst ructed fr omt hemI n addi t i on, a st udy of t he ef f ect ofper f or at i ons on var i ous proper t i es of t hel amnat e and model cabl es was i ni t i ated, thei dea bei ng that per f orat i ons woul d i mprovedr yi ng and i mpr egnat i on character i st i csw t hout i mpai r i ng el ect r i cal per f ormance.2. PHYSI CAL PROPERTI ESThe physi cal pr opert i es of t he PPL' s andcel l ul ose paper wer e compared as shown i nTabl e I . The PPL' s are essent i al l y apaper/polypropylene/paper composi t e. For t hemost par t , physi cal proper t i es were measuredw th an I nst r on Mat er i al s Test i ng SystemModel 4 2 0 6 . Thi s comput er i zed equi pmentfaci l i t ates custom tai l or i ng of tes tparameters i n compl i ance w t h ASTM methods.3 MECHANI CAL PROPERTI ES3. 1 SWELLI NG CHARACTERI STI CSA qual i t at i ve swel l i ng t est was per f or med ont he PPL' s. Thi s was done by l appi ng t hel amnat es ont o a 1. 6 cm di amet er t ubul aral umnum conductor to an i nsul at i ont hi ckness of 1 . 2 5 cm The rol l s were vacuumdr i ed and i mpregnated w t h Pol ybutene 015i mpr egnat i ng oi l and subsequent l y subj ectedto short - t er m agi ng ( 1 l O O C for 7 days) i nPol ybutene 06 pi pe f i l l i ng oi l [ l ] . Al l t hr eel amnat es remai ned i ntact and exper i enced nor upt ure of tape. c3.2 DELAM NATI ONDel amnati on i s def i ned as t he separat i on ofei t her paper l ayer f romt he pol ypropyl ene.

197 0-7803-0649-X/92 3.00 992 IEEE


2/6

TABLE I : Physi cal Propert i es of Lamnates and Cel l ul ose Paper~~

PROPERTYThickness,Width, mm

Density, g/cm3Paper Density, g/Cm3

Paper by WeightPaper by Thickness

Tensile Strength,N I mm (MD)

Elongation, (MD)Elastic Modulus,

Mg/cm2Compressive Modulus,(at 2.0 kg/cm2 radialkg /cm2pressure)coefficient of frictionStaticJkineticPolypropylene MeltTemp erature, CAnalysis ofPolypropylene

Dielectric Constant,UnagedIAged

LAMINATE A0.1316

0.890.884750

8.21.3

67

81

0.5210. SO

159

IsostaticHomo-polymer2.812.8

AMINATE B0.1519

0.890.744040

8.41.4

56

101

0.5310.49

159

IsostaticHomo-polymer2.712.6

,AMINATE C0.1420

0.840.755536

9.8 1.5

63

81

0.S910.51

159

IsostaticHomo-polymer2 -712.7

ELLULOSE0.1627

0.800.78100100

9.51.6

69

70

0.45/0.42

--

3.51-

NOTESASTM D202

ASTM D202ASTM D202

ASTM D202ASTM D202

ASTM D202

PirellimethodASTM D1894

DSC

Infraredspectroscopy

fromcapacitancemeasurementson modelcables

MD Machi ne D recti on< > 1 per f orati on of 1.27mm di ameter per 25mm of l amnat e

TABLE 11: Del amnat i on Character i st i cs of Lam nat es.Qual i t ati ve and Quant i t ati ve Eval uati on of I nt er- l ayer BondSt rengt h.

METHOD OFEVALUATI ON90 PeelTest90 PeelTest90 PeelTestAEI C CS2-90AEI C CS2-90

CONDI TI ON OFLAM NATEas r ecei ved

aft er i mpregnati onand short - t ermagi ngaft er i mpregnati onand l ong- t ermagi ngaft er i mpregnati onand shor t - t ermagi ngaf t er i mpregnati onand l ong- t ermagi ng

I NTER( I NSLAM NATE A0.35/0.51

0 1810 20

-10.17

nodel amnati onnodel am nat i on

LYER BOND STRENGTH, N/ 15mmIE LAYER/ OUTSLAM NATE Bo .14/o. 18

0. 11/ 0. 12

1 0

nodel amnat i oncompl etedel am nat i on

)E LAYER1LAM NATE Co. 8411.07

0 3610 72

1 0.69nodel am nati onnodel amnat i on

198


3/6

Suscept i bi l i ty of t he PPL' s t o del am nat i onwas eval uated as f ol l ows:1) Dry as recei ved- Per f or m90 peel t est2) Af t er i mpr egnati on and short - t erm agi ng- Per f orm 90 peel t est and AEI C CS2- 903) Af t er i mpr egnat i on and l ong- term agi ng

- Perf orm 90 peel t est and AEI C CS2- 90

(7 days at 110Oc)test( 150 days at 105OC)test

3. 2. 1 90 Peel TestThe t est set- up f or t he 90 peel t est i sshown i n Fi gure 1. The t est consi st s off asteni ng t he l amnat e t o a 20 cm di ameterwheel whi ch i s mounted on beari ngs andsecured i n the base of t he I nst ron. The t opl ayer of paper i s then manual l y del amnat edf rom t he pol ypropyl ene and secur ed i n apneumati c gr i p whi ch i s att ached t o thecross head of t he I nst ron. As t he cr oss headt r avel s up ( 30 cmm n) , t he paper i sseparated f r om t he pol ypr opyl ene at aconstant angl e of 90 and the i nterl ayerbond st r engt h i s measured ( TABLE 11) .

measures more t han 30%of t he tape w dth andequal or gr eat er di st ance al ong t he l engt hof t he tape, shal l be consi dered t o havef ai l ed t he test. Cabl e sampl es whi ch exhi bi tt ape f ai l ur es f or 5% or mor e of t he t ot alnumber of cabl e t apes shal l be consi dered t ohave f ai l ed t he t est.An examnat i on of t he resul t s i n Tabl e I1i ndi cat e that Lamnat es A and C retai nedabout 50% of t hei r i nt erl ayer bond st r engt haf t er bot h short - t erm and l ong- t erm agi ng.However, t he fact t hat Lam nate B passed t heAEI C t est af t er t he shor t - t er m agi ng t est ,but not af t er l ong- t er m agi nq, put s t heval i di ty of a short - t erm del am nat i on t esti n questi on.4. MODEL CABLE EVALUATI ON4. 1 MODEL CABLE CONSTRUCTI ONModel cabl es were const ructed by l appi ng 4l ayers of PPL ont o a t ubul ar al um numconductor. The tapes were appl i ed w th abut t space of 5-10% of t ape w dt h at 65/ 35regi str at i on. The PPL' s were handl ed w thpl asti c gl oves so as to avoi d cont amnat i on.Al l model cabl es i ncorporated st r ess cont r olcone term nati ons. For cabl e sampl essubj ected t o hot i mpul se t esti ng, a two-el ect rode system was used; whi l e sampl esfor l ong- term agi ng, a t hr ee- el ectr odeguarded system was empl oyed t o perm taccurate measurement s of di ssi pati on f actorand di el ectr i c constant [2].4. 2 MODEL CABLE DRYI NG AND I MPREGNATI ONModel cabl es constr ucted f rom cel l ul osepaper were vacuum dr i ed at 12OOC f or a

d i r e c l i o n 0 1c r o s sh ead f r o ve t

I

p o l i p r o p y l e f l e ondc e i l u l o s e l o y e r sc e l l u l o s e l a y e r

0.25

wd 0 15L LC I.- I

~

~

aa 0 1v,v.-ig. 1. Set-up for 90peel test.

- z -?-L+L%-*-L-+-0 5

3. 2. 2 AEI C CS2- 90 Del amnat i on Test IThe del amnati on t est speci f i ed by AEI C CS2-90 st at es t he f ol l ow ng: Tapes are t o beremoved one at a t i me f r om a cabl e sampl e.These t apes ar e then, i n the same di r ecti onof t ape curl , coi l ed i n a rol l havi ng adi amet er of 2 i n. ( 5 cm or equi val ent t ot he cabl e cor e whi ch ever i s smal l er. Thet ape i s t hen r eappl i ed t o the cabl e core.

0 ~~ ~ ~~ L0 5 10 15 20

Average Stress kVfmn iLaminate A + Laminate c

+ Laminate B C e l l u l o s e

25

Fig. 2. Dissipation factor vs. stress ofmodel cables at 8 5 T .

Each t ape i s t hen-examned f or separat i on orl oss of bond between the components of t hel amnate. Any such del amnati on whi ch199


4/6

0.25

g 0.2zd 0.15

LLC.-cg 0.1.-nn

0 05a

0

\

I I I I I20 40 60 80 100 120

Temperature, OC+ L o m i n a i e cL a m i n a t e A

L a m i n a t e B U Ce l l u l os e

Fig. 3. Dissipation factor vs. temperatureof model cables at 15 kV/mmaverage stress.

mni mum of 2 4 hours. Si nce PPL' s have a muchl ower moi st ure t r ansm ssi on r ate t hancel l ul ose paper , a mni mumdr yi ng t i me of 7 2hours was al l owed. A 1 hour bl ank-of f t estwas perf ormed as a cri t eri on f or cabl edryness. Thi s consi st ed of bl anki ng off t hekett l e and ensuri ng that t he l oss of vacuumover 1 hour was not more t han 50 pm Once i twas establ i shed t hat model cabl es were dr y,t hey were i mpregnated w t h Pol ybutene 015whi ch was degassed t o appr oxi matel y 10 ppmmoi st ure.4 . 3 DI SSI PATI ON FACTOR VS STRESSModel cabl es i mpregnated w t h Pol ybut ene 015i nsul at i ng oi l were pl aced i n hi gh vol t aget est cel l s cont ai ni ng Pol ybut ene 6 pi pe-f i l l i ng oi l . Di ssi pat i on f actor was measuredas a f uncti on of st r ess at 85OC. Dat a wer erecorded f r om 3 model cabl es at t hi st emper ature f or each l amnate and theaverage di ssi pat i on f actor was t aken. Ther esul t s shown i n Fi gur e 2 i ndi cat e t hatt here i s negl i gi bl e di f f erence bet ween t he 3l am nat es and al l t hr ee l amnates have asi gni f i cantl y l ower di ssi pati on f actor t hancel l ul ose paper.4 . 4 DI SSI PATI ON FACTOR VS TEMPERATUREDi ssi pat i on f actor was measured as af unct i on of t emper atur e at 15 kV/ mm t heexpected operati ng st r ess of a f ul l si zecabl e. These data ( pl ot t ed i n Fi gure 3 )i ndi cat e t hat t he l am nat es have si m l arl oss characteri st i cs and t hat t hese l ossesare substant i al l y l ower t han cel l ul osepaper.

0 2 5

0 I I .0 1 2 3 4Aging Time, hours xlOO0)

L a m i n a t e A + L a m i n a t e c* Lam ina te Ce l l u l os eFig. 4. Aging characteristics of model

cables at 85OC.4 . 5 LONG- TERMAGI NG OF MODEL CABLESModel cabl es were subj ected t o l ong- t ermagi ng t ests at 85O and 105OC, i n order t odetermne t he rel ati ve l ong- term stabi l i tyof t he l amnat es. The model cabl es had anappl i ed el ectr i cal str ess of 20-22.5 kV/ mmf or t he dur ati on of t he test. Thedi ssi pati on f actor andcapaci t ance/ di el ect r i c const ant of modelcabl es at 15 kV/ mm ( oper at i ng st r ess) wasmoni tored t hroughout t he agi ng t est. Theresul t s ar e pl ot t ed i n Fi gur es 4 and 5 al ongw th those f rom a l ong- term agi ng testperf ormed on cel l ul ose paper.Dur i ng t he agi ng test , t wo of t he modelcabl es constr ucted f r om Lam nat e B f ai l ed.Di ssecti on of t he f i r st cabl e di d not r evealsi gns that t he f ai l ur e coul d be at t r i but edt o t he i nsul at i on or cabl e constr ucti on. Thesecond f ai l ure resul ted f roma l ow oi l l eveli n the t est cel l whi ch l ead to el ectr i calt racki ng and the event ual f ai l ure.4 . 6 I MPULSE BREAKDOWN OF UNAGED AND AGEDMODEL CABLESI mpregnat ed model cabl es const r ucted f romt he t hr ee l am nat es were pl aced i n cel l scont ai ni ng Pol ybut ene 6 i nsul at i ng oi l andheated t o 90C. The model cabl es were t hensubj ected t o i mpul ses w t h a 1.5 x 50 swave shape as specified in ASTM D 3 4 2 6 .Br eakdown dat a ar e shown i n Fi gur e 6. Si nce,f or a gi ven t ape, breakdown st rengthdecreases as t hi ckness i ncreases [ 3 ]i mpul se data f or t he l amnat es werenormal i zed t o the thi ckness of t he cel l ul ose

200


5/6

120 ~~~ A - Laminale A B - Laminate BC - Larninoie C D - Cellulose/ ~ ~0 2 5 ~ ~ ~ ~

106 103I

/% E d ____d 0 2S IU.C I(d 0 1 -

v b ._.__. e2 0 1 5 1.-.- A I B C- - + 5& - - l - : - i x L~ _==---*?0 0 5 1 ~ 5 40QE-~ ~ ~ ~~ 20 - I

0 1 2 4Aging Time, hours x1000)0 Aged

Laminale A Laminate CUnagedLaminate B Cellulose

Fig. 5. Aging characterrstics of model Fig. 6. impulse breakdown strength ofunaged and aged model cables.ables at; 105C

t apes. Lam nat e B had an i mpul se breakdownst r engt h 10% hi gher t han cel l ul ose, whereasLamnat es A and C wer e 20%hi gher.4. 6. 1 PERFORATED LAM NATESThe ef f ect of perf orat i ons on i mpul sebreakdown st r engt h of model cabl es was al soi nvesti gated. I ni ti al l y t hi s i nvesti gat i onwas per f ormed on Lam nate A. Perf or at i onswer e made by pushi ng 0. 51 di ameter pi nst hrough t he l amnat e whi ch creat edper f orat i ons w t h a cone-shaped geometr yhavi ng a di ameter of 0. 43 mm and a densi t yof 3 per 25 mm l engt h of t ape. Thi s r esul t edi n a l ower breakdown st r ength, whi ch wast hought t o occur because of t he st r essenhancement associ ated w t h t he perf orat i ongeomet ry. I n order t o determ ne i f t hi s wast he case, model cabl es were const r uct ed w t ht he same l amnat e and per f orat i on l ayout ,however t he per f orat i ons were rol l ed smoot h( or near l y so) bef ore t apes were appl i ed t ot he conduct or. These model cabl es had ahi gher breakdown st r engt h, but st i l l l owert han model cabl es construct ed f romunperf orat ed t apes.I n or der t o eval uate t he ef f ect ofper f orat i on geomet r y on i mpul se breakdown, acyl i ndr i cal - shaped per f orat i on whi ch wasassumed t o provi de a more uni f orm el ectr i cf i el d was used.Per f orat i ons were made w t h a punch whi chl eft a 1 3 mm di ameter hol e. Two set s ofmodel cabl es were const r uct ed f r om LamnateC whi ch contai ned 1 per f or at i on per 25 mmand 2 per f orati ons 25 mm Fi gur e 7i ndi cat es t hat t hZer cyl i ndr i cal - shaped

per f orati ons have not aff ected t he i mpul sebreakdown st r ength of t he model cabl essuggesti ng t hat per f orat i on geometr y has asi gni f i cant i nf l uence on i mpul se breakdown.I ncl uded i n Fi gur e 7 i s a di agr am ofper f orat i on l ayout s and geometr i es.5. DI SCUSSI ONThi s st udy eval uated t he l amnat es as t o t heease w t h whi ch the paper i s del amnatedf rom t he pol ypr opyl ene bot h quant i t at i vel y

9 0 peel t est) and qual i t at i vel y A E I C CS290) . Resul t s i ndi cat e t hat whi l e l am nat es Aand C l ose 50- 70% of t hei r i nt er- l ayer bondst r engt h af t er bot h shor t - t er mand l ong- t ermagi ng test s, t hey retai n enough t o meet t hedel amnat i on r equi r ement speci f i ed i n A E I CCS2-90. Lamnate B, however , seems t o retai nwhat l i t t l e bond st r engt h i t has af t ershor t - t er m agi ng, but not af ter l ong- termagi ng. Thi s suggests t hat a shor t - t er m agi ngt est i s not a r el i abl e met hod t o eval uat ecandi date l amnat es.Resul t s of di ssi pat i on f actor vs str ess,t emper at ure and l ong- t er m agi ng, show t hatt her e i s no appr eci abl e di f f erence bet weenl amnat es A, B and C. However, t he l amnat esi n gener al of f er si gni f i cant advant ages overconvent i onal cel l ul ose paper i n t erms ofl oss characteri sti cs.

201


6/6

a79 7

Lamina te A

101

i i

Z

V - U q p e r f o r a t e d laminateX-2 perf125 mm smoothed)2-2 pe r t 1.27 mm dra)lZ5 rnm

W 4 erf125 mrn unsrnooihsd)Y-1 pe r f 1 7 rnrn dla)1 5 nm

Fig. 7 mpulse breakdown strength ofmodel cables constructed withperforated laminates.

Resul t s fr om t he study of perf oratedl amnates i ndi cate t hat i mpul se br eakdownst r ength i s r educed when per f orat i ons have ar ai sed or cone-shaped geometr y. Thi s i st hought t o occur as a r esul t of t he enhancedel ectr i c f i el d gradi ent. Thi s i s suppor t edby i mpul se breakdown data f or model cabl esconst ructed f r om Lamnate C whi ch have al ar ger , yet mor e uni f orm cyl i ndri cal - shapedperf or at i on.Whi l e t he resul t s i ndi cat e that perf orati onshad a margi nal ef f ect on t he physi calproper t i es of t he l am nat es, i t i s expectedt hat t he mechani cal pr opert i es ( especi al l ybendi ng char acteri sti cs) of f ul l - si ze cabl eswoul d be i mpai red. Future work shoul d f ocuson t hi s aspect of t he cabl e desi gn.On t he basi s of t he data avai l abl e, i t canbe seen t hat l ong- t erm agi ng di d not r educet he i mpul se br eakdown st r ength of modelcabl es ( Fi g. 6). Dur i ng the ear l y st ages ofl ong- term agi ng, t he di ssi pat i on f actor oft he model cabl es showed an i ni t i al decr ease.Thi s phenomenon has been associ ated w t hvol t age condi t i oni ng as report ed by Bl odget tet a1 [ 4 ] .

6.1)

4)

CONCLUSI ONSAl l t hr ee l amnat es exhi bi t ed markedl yl ower l oss char act er i st i cs t hancel l ul ose paper. The di ssi pat i on f actoras a f unct i on of st r ess, t emper atur e andagi ng t i me was 113 t hat of cel l ul osepaper.Lam nates A and C had approxi matel yequi val ent i mpul se br eakdown st r engthswhi ch were approxi matel y 20% hi gher t hancel l ul ose paper . Lam nat e B was onl y 10hi gher t han cel l ul ose paper.Del am nati on of t he l am nates di d noteff ect br eakdown st r engt h or l osscharact eri st i cs, but woul d most probabl yi mpai r t he mechani cal char act eri st i cs ofa f ul l - si ze cabl e ( t her momechani calbendi ng pr oper t i es i n part i cul ar ) [ 5 ] .The per f orat i on geometr y had asi gni f i cant i nf l uence on i mpul sebreakdown st r engt h, w t h cyl i ndri cal -shaped per f or ati ons bei ng l ess harm ult han cone- shaped per f orati ons.

REFERENCES:1.

2 .

3

4 .

5 .

J . C. Chan, K. Haj r a and Z. S. Pani r i ,Pol ypr opyl ene/ Paper Lam nat es as Hi ghVol t age Power Cabl e I nsul at i on8I ,Conf erence Recor d of 1984 I EEEI nt er nat i onal Symposi um on El ectr i calI nsul at i on, Mont r eal , J une 11-13, 1984.J C Chan and K. Haj r a, I I Eff ects ofConduct or Screeni ng and O l - Types on t heEl ectr i cal Char act er i st i cs of ModelCabl es , I EEE Tr ans. on El ectr. I nsul . ,VOL. El-16, No. 5, Oct ober 1981.H. C. Hal l and D. Ski pper, ' I The I mpul seSt r engt h of Lapped I mpregnated PaperD el ectr i cI f , The Pr oceedi ngs of I EE,Vol . 103, Par t A, No. 12, Dec. 1956.R. B. Bl odget t and F.H. Goodi ng,Par ameters Af f ect i ng t he I ncrease i nDi el ectr i c Lo s s Due t o Car bon Bl ackPaper Screens f or O l - PaperDi el ect r i cs I EEE Summer GeneralMeet i ng and Nucl ear Radi ati on Ef f ectsConf erence, Tor ont o, Ont ar i o. , J une1963.V. A. A. Banks and A. C. G Secr ett ,Pl asti c-Paper Lamnat e f or O l Fi l l edCabl es , I EE, Di el ectr i c Mat eri al s,Measurement s and Appl i cati ons, J ul y1975.

202

mechanical and electrical performance of polypropylene paper laminates versus cellulose paper for...

Documents