Overvoltages caused by circuit braker's poles lagging during switching operation of unloaded power transformer

Ovaj rad obrađuje utjecaj prenapona uzrokovanih kašnjenjem polova prekidača prilikom uključenja transformatora u praznom hodu na električne aparate u transformatorskom polju. Kako bi se mogla izvršiti analiza ovih prenapona na računalu potrebno je sačiniti odgovarajući model energetskog transformatora. Model transformatora za analize uklapanja transformatora u praznom hodu mora sačinjavati adekvatno modeliranu krivulju magnetiziranja transformatora. Stoga je predstavljena jednostavana metoda za određivanje krivulje magnetiziranja transformatora na temelju rezultata pokusa praznog hoda koji su dostupni iz ispitnog protokola transformatora. Navedena metoda ustvari predstavlja rješavanje problema optimizacije u kojem je potrebno pronaći koliko krivulja dobijena proračunom odgovara onoj dobijenoj mjerenjem. U svrhu rješavanja problema optimizacije napravljen je računalni program u programskom paketu MatLab koji koristi metodu evolucijskog algoritma. Dobijeni rezultati su zatim primijenjeni za modeliranje krivulje magnetiziranja transformatora u programskom paketu EMTP/RV, te su predstavljeni rezultati simulacija kašnjenja polova prekidača prilikom uključenja modeliranog transformatora u praznom hodu. Rezultati provednih simulacija su pokazali da usljed kašnjenja polova prekidača prilikom uključenja transformatora u praznom hodu može doći do nastanka prenapona uzrokovanih serijskom rezonancijom ili ferorezonancijom, a zatim, ovisno o trenutku uključenja polova koji kasne, i do pojave prenapona vrlo brzog porasta čela vala. Konačno, prikazan je utjecaj prenapona uzrokovanih kašnjenjem polova prekidača prilikom uključenja transformatora u praznom hodu na električne aparate (strujne transformatore i odvodnike prenapona) u transformatorskom polju za dva slučaja zabilježena u postojenjima Elektroprenosa BiH.This paper shows influence of overvoltages caused by circuit breaker's poles lagging during switching operation of unloaded power transformer on electrical apparatus in transformer bay. In order to perform analysis of these overvoltages on personal computer it is essential to create appropriate power transformer model. Power transformer model for analysis of unloaded transformer switching must comprise adequately modelled power transformer's magnetising curve. Therefore simple method for power transformer's magnetising curve representation is presented based on results of open circuit test on power transformer that is available from transformer testing protocol. In reality this is optimisation problem that shows how much is curve calculated by computer simulation close to the one obtained by measurement. To solve this optimisation problem computer program was created by MatLab software based on evolutionary algorithm. Its results were used to model power transformer's magnetizing curve in EMTP/RV software and simulation results of one of circuit breaker's poles lagging during switching operation of modelled unloaded power transformer are presented. Simulation results showed that circuit breaker’s poles lagging during switching operation of unloaded power transformer could cause serial resonance or feroresonance induced overvoltages and then steep front of the vave overvoltages could occur depending on moment of circuit breaker’s contacts closure. Finally, influence of overvoltages caused by circuit breaker's poles lagging during switching operation of unloaded power transformer on electrical apparatus (current transformers and surge arresters) in transformer bay is shown on two cases encountered in Elektroprenos's BiH substations.nsformer, modelling, magnetizing curve, evolutionary algorithm, current transformer, surge arrester