Effects of grading capacitors of CBs on inception ferroresonance in power transformers

The study of magnetic circuits is of great importance in electrical engineering. Many of these circuits are highly nonlinear allowing coexisting stable solutions. This may lead to sudden and dramatic changes in the response when the system is disturbed and ferroresonance occurs. In order to predict ferroresonance behavior in a network, it is important that the magnetization characteristic of the inductors and steel cores are accurately modeled since this is the main nonlinearity in the system. In this paper a hysteretic inductor has been represented based on Preisach theory. Using this inductor, a high voltage power transformer has been modeled and effects of grading capacitors of the circuit breakers on occurrence of ferroresonance, while the transformer is fed through a transmission line, have been discussed. Simulations show that different ferroresonance modes could occur in this transformer and in these, hysteresis, grading capacitors and the transformer winding capacitance have important roles.