Analysis of lightning overvoltages on power transformers

Diplomski rad opisuje i analizira neke od ključnih utjecaja atmosferskih prenapona na tipične energetske transformatore kakvi se koriste u postrojenjima za prijenos i distribuciju električne energije. Za potrebe rada izrađen je detaljni model transformatorske stanice 220/110 kV kako bi se sam utjecaj prenapona mogao promatrati tokom pogona. Posebna je pažnja posvećena modeliranju transformatorske stanice i energetskog transformatora kao elementa od ključnog značaja. Promatrana su dva različita modela transformatora na kojima su izračunati preneseni atmosferski prenaponi u praznom hodu i u pogonu transformatora. Simulacije su se temeljile na stvarno izmjerenim prenaponima u postrojenju i time se otvorila mogućnost usporedbe dobivenih rezultata sa zabilježenim događajima u pogonu. Cilj rada bio je uvidjeti sličnosti i razlike u ponašanju visokofrekvencijskog i niskofrekvencijskog BCTRAN modela transformatora proširenog sa kapacitetima za različite valne oblike atmosferskih prenapona.The objective of this master thesis is to describe and show some of the key factors of influence of lightning overvoltages on typical power transformers which are used transmission and distribution substations. A detailed simulation model of the substation 220/110 kV has been developed for the purpose of the thesis, in order to analyze the influence of overvoltages on transformers in operation. A special attention has been paid to the modelling of the substation and power transformer as the most important element. Two different models of power transformers have been used for calculation of transmitted overvoltages in case of unloaded transformer and while in operation. Simulations have been based on the real measured overvoltages in the substation which opened up the possibility to compare the obtained results with the recorded overvoltages at power transformer terminals while in operation. The aim of this analysis is to identify differences and similarities between high-frequency and low-frequency BCTRAN (extended with capacitances) models of power transformers with respect to different lightning overvoltage waveforms