HYBRID MODELING OF INHOMOGENEOUS TRANSFORMER WINDINGS FOR VERY FAST TRANSIENT OVERVOLTAGE STUDIES

This paper presents a novel approach for modelling transformer winding s, which is valid in the frequency range of 10 kHz to a few MHz. It is a hybrid model; Coil-by-Coil Detailed pins inter-coil Black Box Model . The parameter estimation of the Detailed Model and the synthesis of the Black Box Model is based on frequency domain measurements. The tec hnique is applied to a high voltage transformer winding. The compariso n of the measurements and the frequency domain simulation of the model with EMTP confirms the validity and accuracy of the model for the int ended frequency range. Experiments in the frequency range of several M Hz reveal that remarkable overvoltages appear at the connecting point of the inverted and interleaved part of this winding. It is shown that the reason of the VFTO (Very Fast Transient Overvoltage) in the MHz r ange is the inhomogeneity of the winding parts.