MONITORING OF DIELECTRIC LOSSES AT CAPACITOR-TYPE BUSHINGS

Transcription

1 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu MONTONG OF DELECTC LOSSES AT CAPACTO-TYPE BUSHNGS DOEL NEDELCUT, sch, Dvlopmnt n Tsting Ntionl nstitut fo Elcticl Engining CMET Ciov, Cl Bucusti, 44 OMANA nlcut@icmt.o DUMTU SACEDOTANU sch, Dvlopmnt n Tsting Ntionl nstitut fo Elcticl Engining CMET Ciov, Cl Bucusti, 44 OMANA mico@icmt.o Abstct: - At psnt, th tnncy to implmnt th conition-bs mintnnc (CBM, which llows th optimition of th xpnss fo quipmnt monitoing, is mo n mo vint; lso, th tnsfom substtions with mot monitoing incsingly us. This pp viws ll th vntgs of th on-lin monitoing n psnts n quipmnt fo on-lin monitoing of bushings, which is th own contibution of spcilists who th uthos of this pp. Th pp psnts stuy of th tmptu fil, using th finit lmnt mtho. Fo cying out this stuy, th 3D molling of th bov mntion bushing ws pfom. Th nlysis stuy is on ting into ccount th xtm thml stsss, focusing t th lvl of th fist cooling wing sction of th cmic insulto. This fct nbls to justify th tnδ vition in tim, pning on th tnsfom loing n th nvionmntl conitions. Ky wos: - Bushing; cpcito; insulto; tnsfom. ntouction Pow tnsmission n istibution systms fom th conomiclly vlop countis ly g bing, in mny css, mo thn 3 ys ol. All th fix ssts of th pow systms hv stni lif tim of mximum 3 ys. Fom now on, ny quipmnt is in ng to fil t ny tims with no pvious wning. Un ths conitions th on-lin monitoing is on of th most usful mthos fo polonging th lif tim up to th filu tim limit n fo plcing th ssts o coving thm in th lst momnt. Bcus th bushing is y lmnt in th option of lcticl pow quipmnt, its sf option is spcil issu bcus its gtion ls, in mny css, to th xplosions follow by fis with vy gv consquncs fo th sttions n th substtions. f up to th psnt th tim-bs mintnnc (TBM, with pioicl visions, ws us, in th lst ys on tis to fin solutions to pss to th conition-bs mintnnc (CBM which llows th minimition of th costs, th polongtion of quipmnt lif tim n th cs of th iss of filu in xploittion with gv consquncs. Bs on th uthos xpinc in th fil of monitoing of lctic ntwos pmts n pow tnsfoms thml conition [], igitl quipmnt fo th monitoing of bushings insultion, with n oiginl concption, ws finli.. Contibutions to th conition-bs mintnnc of th bushings by thi monitoing.. Th impotnc of on-lin monitoing of bushings Th mg of bushings is on of th min cuss ling to th impop option of th tnsfoms o vn to th xplosions. Th sttistics confim tht 3% of th tnsfom mgs u to cpcitotyp bushings. Th Euopn sttistics show tht 8% of th mg bushings btwn n ys ol n thfo th monitoing is ncssy vn SSN: ssu 5, Volum 3, My 7

2 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu bfo th mil of thi lif tim []. Th high lctic fil gints in th bushing insultion n th high woing tmptu contibut to th ccltion of insultion ging. Th xplosion of th bushing cn mg th tnsfom tn, cn gnt n xtn fi by tnsfom oil ignition, n fi in th bunl of cbls in th lctic switch box o in th contol oom though th scony wiing. A mg of th bushing ls to finncil losss (btwn n 3 million of olls to th insus, both fo physicl mgs n fo th istubncs of th ffis in th compnis thy sving.. Ths losss cn ch, in xcptionl situtions, tns million of olls. Th xplosion cn gnt mtil mgs n humn lif losss bcus of th poclin pics sp t long istnc n with vy high sp. Th titionl ignosis systms of th bushing insultion bs on pioicl msumnts of insultion loss fcto, onc within -3 ys. n such cs, it is ncssy to put th tnsfoms out of svic n to msu tnδ t n ppli voltg of V. Th isvntgs of this titionl mtho fo monitoing th bushing insultion th following: -Th tsting fquncy bitily chosn is not usully colt with th filu t vlopmnt. Th pctic pov tht th pio btwn th msumnts must not xc ys to tct 95% fom th fctiv bushings, n this is pcticlly unccptbl; -Th msumnts fo tnδ pfom t n ppli voltg of V not lvnt fo th ctul conition of th bushing insultion. Th msumnts t t voltg, pfom on th bushings wh ptil ischgs pp, show vlus of 5-8 tims high thn thos msu t V. Th oil tiotion t high tmptus gnts chmicl moifictions n simnt ccumultions ling to th filus of th bushings. Th tction of this typ of fult t th voltg of V cn b vy ifficult, vn by tnδ msumnt t th t voltg. -Th titionl tsting mthos qui lot of wo n th putting out of svic fo long tim. By ths sons it is pfbl to us on-lin monitoing mthos fo th bushings. Bushing monitoing mthos nown t psnt psnt blow: - us of moifi Sching big, wh spcil mthos tn fo suppssing th istubncs (stn cpcito suppli t th low voltg si of voltg tnsfom connct on th sm phs s th tst objct, plcmnt of th convntionl null inicto by micocontoll-bs msuing vic fitt out with ptiv filttion.th quipmnt hs in its stuctu stn componnts which qui spcil mtologicl vifictions, is buly n coul b chiv with high costs. Th quipmnt chiv by this mtho implmnttion llows monitoing th ilctic issiption fcto (tn δ, but is vy xpnsiv. - vcto ition of th cpcitiv cunts of th bushings mount on th th phss n tction of th unblnc cunt (Fig. Figu - Bloc igm of cpcitiv cunt cquisition Wh: A, B, C bushings un potntil C - min cpcity of th bushing C - cpcity of th lst ly of th bushing,, - cpcitiv cunts cqui t th A B C bushing msuing tminls - vcto On th bsis of th nlysis on th mgnitu n phs of th unblnc cunt (Fig. th g of moifiction fo th ilctic poptis of bushings is foun; th isvntg is tht it os not psnt on lin th vlu of tn δ fo ch bushing. SSN: ssu 5, Volum 3, My 7

3 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu b c blnc bushings b tmintion of th initil unblnc cunt, ; c tmintion of th unblnc cunt, n sum cunt, ting lso into ccount th initil unblnc cunt ; tmintion of th unblnc cunt, moulus n phs, lt th phs B Figu - Dtmintion of th unblnc cunt wh : p th spcific volum losss (v th volum of ilctic t th tmptu n, t th stss with th lctic fil hving th stngth E: P p v E p S E p S E (6 U E E S π f U C π f E ε ε (7 π f ε o ε S E p tn δ (8 π f ε ε Th phso igm is psnt in th figu 3: c 3. Digitl quipmnt fo on-lin monitoing of bushings Fo on-lin monitoing of bushings it is il to monito th tim vition of ilctic losss n of bushings own cpcity. n qusi-homognous ilctic, in homognous lctic fil, th losss in ilctic pn on th lctic fil stngth n tmptu. Th losss incs popotionlly to th squ of th lctic fil stngth but thy stongly pn lso on th tmptu in ilctic [6], [8]. P( ε ε ( E ω tn δ( (4 At high lctic fils, th losss hv vn mo ccntut incs lt to th lctic fil stngth. Th ht pouc by Joul losss fom th cntl conucto of th bushing gnt lso tmptu is in th insulting mtil, which ovlps on tht on u to th ilctic losss. Bcus of ilctic losss, th ltnting cunt which psss though bushing is not puly ctiv, but it hs n ctiv componnt nm lg cunt. Lt us consi n lmnty cpcito with th i of th mtu S, th thicnss, t th voltg U n th fquncy f, which hs th losss P: P p v E (5 Figu 3 Th phso igm Th ilctic losss of bushing : P U U tn δ π f U C tn δ (9 Th us msuing igm psnt in th figu 4 is th clssicl on. C C U x U U y U x U y bu C, C - bushing o CT un tst, - high voltg sistiv ivi (cpcitiv ivi o voltg tnsfom - itionl shunt sisto << XC Aft clibtion φ[ux,uy] ~ tgδ Figu 4 Th msuing igm Th quipmnt, [9] (Fig.6, is compos by n unit fo signls conitioning n pttion (UCAS, which ts ov th cunt infomtion fom th tst tps of th tnsfom bushings though th pts Ac(A, Ac(B, Ac(C, Ac(, Ac(b, Ac(c n th fnc SSN: ssu 5, Volum 3, My 7

4 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu voltg infomtion cosponing to ch bushing, fom th scony msuing wining of msuing voltg tnsfoms though th pts A U (A, A U (B, A U (C, A U (, A U (b, A U (c n pplis thm t th inputs of two micocontolls which pfom th smpling, th stog n th tnsmission of th signls though th pting blocs (BA, (BA, (MUX tows th micocontoll of th cntl pocssing unit (UC. Ths ons pfom th clcultion of th ilctic loss fcto, using Foui sis lgoithm fo th composition of th nonsinusoil pioic cunt n voltg signls, msumnt of phs isplcmnt btwn th funmntls of th voltg n cunt signls, th clcultion n th isply of tn δ n cunts msu t th tminls on th lphnumic isply (LCD, th ction of t bs in th xtnl mmoy of th cntl unit, th gntion of light signls n ngiing of ly contcts whn xcing th thshols t fo lm, th communiction with comptibl comput BM-PC fo th t visulition, th stting of pmts, lms n th chiv ownloing. Th popos solution hs th following vntgs: - it solvs th poblm of monitoing th volution of loss ilctic fcto, tn δ, cunt t th tminls of th bushings ffnt to th pow tnsfoms; - it llows th intifiction of th bushing with high ilctic losss by ctivting th cosponing lm; - it cis out th jction of th istubncs gnt by climtic n lctic fctos, by th implmnttion of numicl cusiv filt; - it llows th clcultion of th bushing own cpcity n its monitoing. Th voltg pts stp-own tnsfoms spcilly clcult without phs ngl o in th msuing ng. Ths ons ssu: - th pcticl limintion of th phs isplcmnts btwn th pimy n th scony; - th limintion of th th loops; - th limintion of th istubing signls. To limint th phs iffnc on th scony on mounts sistiv lo in o to cy out constnt consumption n to limint th tim vition of th phs iffncs. Figu 5 Th bloc igm of on-lin monitoing quipmnt fo tn δ Th cunt pts pfom th convsion of th bushing lg cunt in voltg signl in phs with tht on. Thi constuction is compct n thy plc th shot-cicuiting switch xisting t th msuing tminl of th bushing chiving th sm potction g. Th convsion is on by non-inuctiv sistiv lmnts n vy low cpcitis. Ov-voltg potctiv lmnts fosn. Fo ch monito bushing th mtho psums th cquisition of two signls: on signl tn ov fom th tst tp of th bushing n th scon signl, psnting th fnc voltg, tn ov fom th instumnt tnsfom cosponing to th monito bushing [3]. Th tn ov signls hv non-sinusoil pioicl chct n thy hv th following fom: [ M cos( ωt + N sin( ω ] f (t A ( + t Th implmnt pogm pfoms th clcultion of tn δ by th xtction of funmntls fom th smpl signls by Foui nlysis lgoithm. Th clcultion lgoithm psums: - tmintion of th cofficints M n N fo th funmntls of th two signls ( T M f (t cos( ωt t ( T T N f (t sin( ωt t ( T Th cofficints M n N tmin fo ch cqui quntity. SSN: ssu 5, Volum 3, My 7

5 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu - tmintion of initil phss of th funmntls ' M ' M ϕ ctn (3 ϕ ctn ' N N (4 wh, ϕ th initil phs of th funmntl of th signl tn ov fom th msuing tminl of th bushing; ϕ ' th initil phs of th funmntl of fnc signl tn ov fom th msuing tminls of th voltg tnsfom cosponing to th msu bushing. ' Noting: δ ϕ ϕ (5 Th loss ilctic fcto is: tn δ tn( 9 δ (6 Fo non-sinusoil stt w hv: u it C (7 u i C t CωU (8 Fom h: CωU (9 Thus, by clcultion, th own cpcity of th bushing is obtin. Figu 6 Monitoing quipmnt mount in th sttion 4. Clcultion of bushing hting un long tim uty n thml cpcity Th clcultion is pfom in coving mnn, supposing tht th xil thml flux is nglct, but ting into ccount th Joul losss in th tminl n th ilctic losss in th cpcito, lso thi vition with tmptu. Th xtnl tmptu is consi s bing givn:. Th clcultion mol is psnt in Figu 7. Th t cunt N flows though th tminl with imt, gnting on th unit of lngth th Joul losss []: 4 P ρ ( + N ( π Figu 7 Bushing clcultion mol H, is th sin ffct fcto, ρ is th sistivity of th tminl mtil n is th tmptu cofficint t C, n is th tminl tmptu in C. Futh on, th incsing fcto fo th sistnc of th soli cicul cylinicl conucto is clcult. On consis th cs th soli cicul cylinicl conucto with imt, sistivity ρ n tmptu cofficint t th fnc tmptu n ltiv pmbility µ, in sinusoil ltnting cunt hving th fquncy f. On clcults fistly th sistivity ρ n th tmptu cofficint t C: ρ ρ (, ( On nots: π f µ µ ξ ( 4 ρ ξ ξ + (3 if is th conucto tmptu. Fom th thoy of th sin ffct, th following xpssion of th complx inn impnc of th cylinicl conucto is st: SSN: ssu 5, Volum 3, My 7

6 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu Z i l i + j X l i l ; ζ J J ( ζ ( ζ (4 wh l is th ict cunt sistnc of th conucto: 4 l l ρ ( + (5 π By ζ th complx vibl ws symboli: 3/ ζ ξ j (6 n J n J Bssl functions of fist in, o n. Ting into ccount th shp of th sis giving ths functions: ( ( J ζ ζ (7! ( ζ ( ( (! ( + J ζ ζ Th following xpssion is iv: (8 4 6 ζ + ζ ζ + K ( u + j v ζ + ζ ζ + K b ( x + j y 44 (9 Th cofficints of th sis fom th numto n nominto tmin stp by stp, using th lgoithm: n thn ζ + şi b + + (3 spctivly u n thn u x v y x, v ξ, y, u ξ (3 Th sis bing with oscillting sign tms, thy until th moulus of th tm css blow th moulus of th sum multipli with ltiv tolnc. Th lgoithm is stbl on, in simpl ccucy, up to ξ 5, limit sufficint fo pctic. Futh on, symptotic vlopmnts coul b us. Th fcto fo incsing th sistnc,, psnts th l pt of th fcto. l i ( (3 l Not th fcto hs th significnc j x x +, wh x is th inn ctnc t l x ξ ict cunt istibution: to th l cylinicl conucto. x is th fcto fo chnging th inn ctnc of th cylinicl conucto, u to th sin ffct. Obsvtion Fo bushings with t cunts up to 5 A th sin ffct within th cunt pth coul b nglct. Coming bc to th Figu 7, th tminl is insi th guiing tub with inn imt i. t sults thml sistnc p unit of lngth: i i ln (33 π λu π λu i + Tows th nvionmnt, th tminl is boun by flng with out imt f n it tnsmits ht to th nvionmnt with tmptu by ls fcto (6-3 W/m C. t sults thml sistnc p unit of lngth (34 π f f th bushing flng is fix on th tnsfom tn, on coul consi, n fo th mximum tmptu of th oil t th lvl of tnsfom cp ( 9 C is tn. Th cpcito bushing itslf is m of n lys numb...n, fom insi tows outsi. Th ly numb by is compis btwn th imts - n, hs mil tmptu, th voltg U is ppli on it; ilctic losss p unit of lngth, P, vlop within th ly. On ch imt n nclosu (foil with xil lngth l is loct. Th gomtic pmnc p unit of lngth fo th ly is symboli by Λ : π + Λ π, (,n (35 ln Th ilctic losss p unit of lngth fo th ly xpss s: σ P p Λ U,, n (36 ( ( wh p is th volum nsity of th ilctic losss t fnc tmptu n fo th unit of lctic fil stngth, n σ is th tmptu cofficint fo th xponntil vition of spcific losss. SSN: ssu 5, Volum 3, My 7

7 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu Not n gnl, th ltion fom blow is vli: p π f ε ε tgδ (37 wh f is th fquncy, ε is th vcuum pmittivity, ε is th ilctic ltiv pmittivity n δ is th loss ngl. Th voltg U ppli to th ly sults fom th voltg U m ppli to th bushing S U U m n, (,n (38 S i i wh by S th lstnc of th ly ws xpss: S ε ε Λ l, (, n (39 By ε it ws not th ltiv pmittivity of th ilctic fom ly, which my pn on th tmptu by mns of th ltion: ζ ( ε, (,n ε (4 ε is th ltiv pmittivity of th ilctic t th fnc tmptu, n ζ is th tmptu cofficint. Th thml sistnc of th ly is xpss by th ltion:, (, n + (4 λ Λ wh λ is th thml conuctibility of th ilctic. Th igm fo bushing hting clcultion is givn in Figu 8: On ms th nottions: + n ' (, n -; Z + ' + Z + + ; Z, n + (4 Figu 8 Digm fo bushing hting clcultion wh by ' ' şi th w xpss th thml sistncs of th possibl buff lys, no voltg, fom bushing insi n outsi (clcult by th ltion 4 Tmptus immitly tmin by th ltion: (,n + + Z Pi, (43 i Bcus losss pn on tmptu, ictly o by mns of voltg istibution on lys, th solution (43 is ittivly sum, cocting ch tim th losss in cconc with th pviously clcult tmptus, until sttiony solution (fix point is got. Duing th xpimnttions impovmnts w m in o to uc th influnc of tn δ vition with th lo, with th nvionmnt fctos n with th lctomgntic istubncs, filting th istubing influncs [4], [], [], [3]. t is ncssy to gt th vition tnncy fom th monito t, using n qut filt fo liminting th influncs of th istubing fctos n fo llowing to pss only th slowly vibl componnt of th losss in th min insultion. Without ny influnc, th vition of th ilctic loss fcto sis woul b vy slow. Bcus of th influnc of vyy n ssonl vitions of th nvionmnt tmptu n humiity th vition of th ilctic loss fcto is cyclic. Bsis, fo th influnc of th nom ffct of signl n lctomgntic istubncs tnsmission to substtion, th mny singul points in th t. Thfo th sis of th on-lin monito ilctic loss fcto (tnδ m cn b compos in th following wy [7]: tnδ m (t tnδ(t + tnδ w (t + tnδ (t (44 wh: -tnδ(t is th min componnt which flcts th ctul conition of th insultion which cn b consi s th componnt with slow vition; - tnδ w (t is th componnt which flcts th vyy n ssonl influncs on th nvionmnt n of oth fctos with slow vition (.g. th lo vition n cn b consi s th low fquncy componnt; - tnδ (t is th componnt which flcts th influncs of th nom fctos incluing unusul climtic conitions, lctomgntic istubncs, tc. (its fquncy bn is wi n in th gtst pt it is in th high fquncy sction. f th tnncy fo tnδ(t cn b uct fom th initil t, th fficincy of th fult ignosis cn b much impov. f n qut softw cunt SSN: ssu 5, Volum 3, My 7

8 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu filt is ppli ch componnt cn b got ictly fom th loss cofficint sis. Th ilctic loss fcto, tnδ, is filt ccoing to th ltion: tn δ pm tn δ p tn δ p tn δ p + (45 wh: tn δ p th psnt isply vlu tn δ p- th pvious vlu (msu n isply tn δ pm th psnt msu vlu th filttion cofficint Th intvl btwn th ings is of th o of minuts. t is possibl to ttnut nom influncs with ltivly shot ution (minuts, hous n possibly ys. As sult tnδ(t is obtin whn both th high fquncy componnt n th low fquncy on limint. Th filttion mtho is usful bcus it ucs th complxity of th ignosis sinc th t cn b ictly pocss, without th n of xtn smpls. Th Figu 9 show, s xmpl, th tim vitions of tnδ in high-voltg substtion t tnsfom of 5 MVA, 4/ V. Figu 9 Th tim vition of tnδ t th bushings on th outputs of 4 V ntu sult: tn tn xp[ ( ] (47 Fo th bushings with sin-lcqu pp insultion, s sults of th lbotoy xpimnts, th vition of tnδ s function of tmptu is s shown in Figu : Figu - Th vition of tnδ s function of tmptu Fom h, th xplntion of th vy high vition of th ilctic losss in th cous of on y n, spcilly, th pnnc on th ntwo lo vition cn b vy clly obtin. Th ppliction of this infomtion is vy usful bcus it confims this ccucy of th msumnts pfom with this monitoing quipmnt plcing confinc in this quipmnt utilition fo potcting th cpcito-typ bushings, th high pow tnsfom, y-fctos in th goo option of pow systms, implicitly. 5. Dpnnc of ilctic loss vition on th lo fctos n nvionmntl conitions By nlysing th got sults, it is notic th inticl bhviou of th ilctic lys, nmly significnt incs of th vg tmptu, u to th incs of th nvionmntl tmptu, spcilly in th hous of lo p (7, vn whn th nvionmntl tmptu css significntly. But th mtil pmt pns lso on th tmptu, ccoing to th ltion: p p xp[ ( ] (46 wh is constnt pning on th ilctic 6. Conclusions This wo psnts th vntgs of on-lin monitoing n spcilly of on-lin continuous monitoing of th bushings on th pow tnsfoms. On-lin monitoing mthos fo th own cpcity of th bushings nown. Ths ons psnt th isvntg tht infomtion concning th vition of th losss in ilctic n implicitly th ging of th insultion is unnown. Oth quipmnt monitos th vcto ition of th cpcitiv cunts though th insultion of th bushings n it tcts thi siul cunt; thus, it is snt infomtion concning th gtion of bushing without SSN: ssu 5, Volum 3, My 7

9 WSEAS TANSACTONS on ENVONMENT n DEVELOPMENT Dol Nlcut, Dumitu Scotinu tcting which on it is.th mtho is us spcilly in th Unit Stts wh th utili bushings with pp mtus hving ppli smiconucting vnish on thm, which migts in tim in oil. Following this isquilibium ll th 3 cpcitotyp bushings plc. Th mtho psnt in this pp llows th ly tction of th fulty bushing n its plcmnt bfo th ppnc of filu ng. At psnt pcs. of this typ of monitoing quipmnt mount n thy continuously monito by th uthos, but until now no non-confomitis w foun in quipmnt option. Th psnt mtho n quipmnt is th objct of utho s ptnt. As sult of th xpimnts, th quipmnt hs bn povi with soft filttion nbling to mov th influnc of lo vition n nvionmntl fctos on th vition of ilctic losss, ming possibl igoous monitoing n just-in tim lm in cs of fult occunc. fncs [] Ash M., slm S.M., Pow tnsfom conition monitoing n ssssmnt fo sttgic bnfits, Cutin Univsity of Tchnology Dptmnt of Elcticl & Comput Engining, Pth, Austli. [] Nlcuţ D., Pop D., Monitoing, Contol n Potction Equipmnt fo Pow Tnsfoms, Woshop Tchnic Qulifiction n Tnsint Bhviou of Componnts of High Voltg Substtion, Klsuh-Gmni,. [3] Nlcuţ D., Minscu A., Scoţinu D., Pătu., Pucu., Equipmnt fo HV Cpcito-Typ Bushings (DPD monitoing, Th 7 th ntntionl Confnc on Liv Mintnnc COLM 4, Bucuşti, omâni, 4. [4]. Nlcuţ D., Bică M., Ţălu M., Monitoing of Cpcito-Typ Bushings Consitions ging th nflunc on Thml Fil Distibution on Dilctic Losss, ASTED Confnc Pow n Engy Systms EuoPES 5, Bnlmn, Spin. [5] Nlcuţ D., Minscu A., Scoţinu D., Pătu., Pucu. - Equipmnt fo on-lin monitoing of cpcito-typ bushings, CGE WOKNG GOUP D. Mting, omni, Efoi,5 [6] oth, A., Hochspnnungstchni, V ition, Win, 959 [7] Wng N., Lu F.C., Li H.M., Anlyticl Pocssing of On-Lin Monito Dissiption Fcto Bs on Mophologicl Filt, EEE, 4 [8] fim A., Noting P., Elctotchnicl Mtils, EDP, Bucuşti, 979 [9] Kuchl A., Numnn C., Koch N., Loppch K., Kus C., Alff J.J., Conition Assssmnt of Ag Tnsfom Bushing nsultions, CGE 6 [] Bic, M., Thmotchnics n ht ngins, Univsiti Publishing Hous, Ciov, [] Zlwci, J., olcj plniov powych n npici i 4 V, PET (96, no 7, pgs 73-8 [] *** Cosmos M..6. Us gui, Stuctul sch n Anlysis Copotion, Los Angls, Clifoni, [3] *** SoliWos. Us gui, Stuctul sch n Anlysis Copotion, Los Angls, Clifoni, 4 SSN: ssu 5, Volum 3, My 7