Achieving the exact equivalent circuit of a large-scale transformer winding using an improved detailed model for partial discharge study

Abstract

Investigating partial discharge (PD) is a critical issue in monitoring the condition of power transformers. For analyzing the transient state behavior of transformer winding, the availability of a model that accurately presents its behavior at high frequencies is necessary. The conventional detailed model is among the models used to perform PD studies. One of the underlying issues of the conventional detailed model is the low frequency validity range of the model, which is limited to about 1 MHz. In this paper, an improved detailed model is presented that overcomes the mentioned problem by adding stray capacitances to the conventional detailed model. A general state-space algorithm is proposed to calculate the reaction of the winding towards the application of the PD signal. In the present study, the frequency-dependent parameters of the improved detailed model have been calculated via the finite element method (FEM). The new methods and ideas are implemented and validated on a real 20 kV distribution transformer winding as well as a 63 kV, 30MV winding. Comparing the results of the proposed model with the waveforms obtained from using PD pulses to both windings in the laboratory environment shows the accuracy and the increased frequency validity range of this model.