High-freqeuncy analysis of three-winding autotransformers 400/121/34 kV

134 Ad ances in Elec ical and Elec onic Enginee ing HIGH-FREQUENCY ANALYSIS OF THREE-WINDING AUTOTRANSFORMERS 400/121/34 kV M. Gu en, M. B and 1) , R. Polanský, P. P os 2) 1) Dep o Measu emen s and Applied Elec ical Enginee ing, Uni e si y o Žilina, Uni e zi ná 1, 010 26 Žilina, Slo ak Republic, E-mail: [email p o ec ed]iza.sk 2) Facul y o Elec ical Enginee ing, ZU Plze, Uni e zi ní 26, 306 14 Plze, Czech Republic, E-mail: [email p o ec ed].cz Summa y This a icle deals wi h a desc ip ion o me hods o an expe imen al analysis conce ning he ac ual condi ion o windings and magne ic ci cui o he au o ans o me , which is equi ed in powe ansmission companies all o e he wo ld. 1. INTRODUCTION Conside ing a signi icance o powe h ee- winding au o ans o me s (see Fig.1) in he elec ic sys em, hei p ice and possible damages a ising in acciden s, i is necessa y o pay a en ion o highe p e en ion o hese de ices. Windings o he au o- ans o me s should be designed o a oid a ious mechanical o he mal de e io a ions caused by sho -ci cui cu en s occu ing in ope a ion. Besides he pe manen de o ma ion e ec s o sho -ci cui cu en , he e is also g adual aging p ocess o he elec ical de ice, which can wo sen i s mechanical p ope ies. Hea shocks can cause de- c ease o mechanical s eng h o ans o me and consequen unexpec ed damage o ans o me du - ing he ope a ion. To p e en a damage s a e o ans o me s, we pe o m di e en ypes o he measu emen s ha should illus a e an ac ual condi ion o he measu ed equipmen . I is he e o e impo an o choose a sui able diagnos ics o he igh p edic ion o such condi ions. Fig.1 The au o ans o me 400/121/34 kV This a icle deals wi h a desc ip ion o me hods o an expe imen al analysis conce ning he ac ual condi ion o windings and magne ic ci cui o he ans o me , which is equi ed in powe ansmission and powe dis ibu ion companies all o e he wo ld. 2. THEORY OF SFRA METHOD AND ITS IMPORTANCE IN TRANSFORMER DIAGNOSTICS SFRA me hod belongs o cu en mos e ec i e analyses and allows o de ec he in luences o sho - ci cui cu en s, o e cu en s and o he e ec s dam- aging ei he winding o magne ic ci cui o he ans- o me . This all can be pe o med wi hou a neces- si y o decomposi ion o de ice and subsequen winding damage de e mina ion, which is e y ime consuming. The me hod o he high- equency analysis (Sweep F equency Response Analyze – SFRA [3]) is also one o he me hods o undisassembling diag- nos ics o ans o me s. No in e en ion o he con- s uc ion o es ed de ice is demanded, he whole measu emen is pe o med on de ached de ice (no unde he ol age). This me hod is applicable mainly o de e mina ion and measu ing immedia ely a e he manu ac u ing o de ice, i.e. o measu ing o e e ence alues. These pa ame e s a e consequen ly compa ed o he o he measu emen s pe o med on he ans o me , which is decommissioned, a e he damages o e isions o ans o me e c. The e is possible o de ec by SFRA:  a de o ma ion o winding and i s mo e- men s,  a sho -ci cui ed u n o opened winding,  a loose swi ching sys em,  a damaged swi ching sys em,  a co e connec ion p oblem  a pa ial b eakdown o winding,  a co e mo emen o i s w ong g ounding. Resul s measu ed on he new ans o me can be used as he e e ence pa ame e s o u he com- pa ison wi h alues measu ed la e a e ce ain ope a ion ime o he ans o me . They can be also compa ed wi h he es esul s pe o med a e he ans o me b eakdown (o a e he n-sho -ci cui s) o epai o i can be used as a diagnos ic es , when ib a ion senso s indica e some po en ial p oblem in ans o me . High- equency analysis o h ee winding au o ans o me s 400/121/34 kV… 135 SFRA as a one o he mos p edic able me hods is based on unc ional high- equency gene a o and spec al eco ding analyze p inciple, which a e se up and con olled by compu e . This me hod is used also by M5100 measu ing sys em (see Fig.2) con- s uc ed by Ame ican DOBLE company [3]. Fig.2 DOBLE M5100 measu ing sys em Acco ding o [2] SFRA me hod de e mines he ans o me esponses in a ime o equency a ea. The ime esponse measu emen p o ides cu e de e mina ion o he ime esponse o he speci ic ol age impulse applied o winding inpu connec- ion. The equency esponse measu emen consis s in de e mina ion o ampli ude e en ually phase e- sponse o he ha monic ol age o a iable equency applied o winding inpu . While he ime esponse is he eco d o ime beha iou o ol age, equency esponse is he ampli ude esponse dependence on equency. A ela ion be ween he esponse and he winding condi ion is de ini e, o he wise i is complica ed. I is impossible o expec he assessmen o conc e e damage o winding om di e ences in esponse beha iou s. The measu emen esul s lead us only o a s a emen o he ac ha some change o winding condi ion eally occu ed. Such es esul s a e e y help ul o decide, whe he i is una oidable o open and e ise he ans o me o no . 3. MEASURING PRINCIPLES The beha iou o ans o me winding esponse e lec s e.g. elec omagne ic couplings be ween he winding and ans o me ank, also be ween he p ima y and seconda y (e en ually e ia y) winding, be ween he windings o pa icula phases o be- ween u ns hemsel es o pa icula windings. The powe ans o me measu emen equi es a se ing up o he equency ange om 10 Hz o 2 MHz, whe eas he e is necessa y o ollow he igh measu ing echnique o p e en a ious inaccu acies and aul s. Acco ding o [2] and [3], measu ing echnique o h ee-winding au o ans o me 400/121/34 kV (Fig.3) is as ollows (see Tab.1). Fig.3 The h ee-winding au o ans o me 400/121/34 kV es ed by SFRA be o e i s ac i a ion Tab. 1 1. OPEN CIRCUIT TESTS 400 kV 121 kV 34 kV e ia y winding Tes 1 Tes 2 Tes 3 Tes 4 Tes 5 Tes 6 Tes 7 Tes 8 Tes 9 A – a B – b C – c a – n b – n c – n 3 – 1 1 – 2 2 – 3 2. SHORT CIRCUIT TESTS a-b-c sho -ci cui ed 1- 2- 3 sho -ci cui ed 1- 2- 3 sho -ci cui ed Tes 10 Tes 11 Tes 12 Tes 13 Tes 14 Tes 15 Tes 16 Tes 17 Tes 18 A – n B – n C – n A – n B – n C – n a – n b – n c – n Du ing he open ci cui es s a mechanical con- di ion o es ed winding and e omagne ic co e is de ec ed. The ollowing cu es ypical o his measu emen p o ide us impo an in o ma ion abou changes in he co e, which a e isible in low equencies, while highe equencies e e o p ob- lems such as winding mo emen s o u n- o- u n aul . Fig.4 illus a es a simula ion o g adual inc ease o u n- o- u n aul s ia open ci cui es on au o- ans o me 400/121/34 kV (see Fig.3) a ans- o me aps o 1, 9, 13 and 17. C B A c b a 1 1 2 1 2 3 N Taps 400 kV 121 kV 34 kV 136 Ad ances in Elec ical and Elec onic Enginee ing The applica ion o analysis o phase a enua ion depending on equency is sui able o mo e com- ple e e alua ion o winding condi ion. This analysis enables o assess he p ocesses o winding mo e- men s du ing he pa icula sho -ci cui s in luences. Fig.4 Simula ion o u n- o- u n aul inc ease by open ci cui es on au o ans o me a ans o me aps o 1, 9, 13 and 17 P oblems wi h co e g ounding o sho ed lami- na es in he co e will ypically change he shape o he lowes sec ion o he cu e ( o 10 kHz). Mid equencies ( om 10 kHz o 200 kHz) ep esen axial o adial mo emen s in he windings and high equencies indica e p oblems such as e. g. winding knocking o p oblems wi h con ac s. Du ing he sho ci cui es s only he winding condi ion in p ima y o seconda y pa o ans- o me is de ec ed. This measu emen no i ies elia- bly o de o ma ion o inne winding and i s mo e- men as a esul e ec s o sho -ci cui cu en s. 4. CONCLUSION P oblem o he equency analysis o ans o m- e s by SFRA me hod is e y comp ehensi e and i s applica ion becomes in e es ing o many ans- o me manu ac u e s and ope a o s. F om he long- e m poin o iew he SFRA me hod is supposed o be e y use ul and i p o ides enough in o ma ion on es ed ans o me s. These ans o me s ha e hei e e ence da a ob ained by he manu ac u e s, sui able o he compa ison wi h u he da a o pa icula ans o me . SFRA es ing me hod ep esen s one o he mos e ec i e al e na i e diagnos ic me hods compa ed o isual check. This me hod allows o de ec he e - ec s o he sho -ci cui cu en s, whe eas we a e able o e alua e he mechanical s eng h ac ion on he ans o me winding du ing p e ious ope a ion I is also possible o iden i y he speci ic winding phase, which has been mos ly in luenced by he sho -ci cui cu en s, wi hou a necessi y o ans- o me di iding, which would be e y ime consum- ing. The e is also possible o iden i y he size o pa- ame e s o ans o me pa allel ci cui as well as he posi ion o i s esonance equency om pa icu- la cu es (see Fig.5). Fig.5 Compa ison o ampli ude a enua ion [dB] and phase cu e [°] in equency dependence (measu emen o he same ans o me winding) REFERENCES [1] K asnika, V., P ocházka, R., Velek, J.: O o aní me ody ek enních cha ak e is ik podmínkach oz oden penoso é sous a y R, In Diagnos ika 05, Plze 2005 [2] Gu en, M., B and , M., Michalík, J.: Analýza ans o má o o zhadom na úinky sk a- o ých p údo , In Diago 07, Os a a, 2007 [3] h p://www.doble.com/p oduc s/sweep_ equen cy_ esponse_analysis.h ml, 15. 1. 2007. [4] Men lík, V., P os , P., Pihe a, J., Polanský, R.: New Possibili ies o he Oil-pape Insula ing Sys ems, In P oceedings o he 20 h No dic In- sula ion Symposium. T ondheim: Tapi Aca- demic P ess, 2007