Effects of transformer core modeling on Partial Discharge current pulses simulation accuracy

Partial Discharge (PD) measurements in Ultra High Frequency (UHF) band requires modern techniques for monitoring of power transformer. This is a topic of interest investigated in this field, especially in recent years. Different experimental models, such as: defect models, and winding models are used in PD studies of power transformer. The purpose in application of these models is to represent and simulate the real transformer performance using a simple model. The proposed model needs to be a simplified one which can be implemented of them. However, the applied simplifications may result in some changes (inaccuracy) into the recorded PD current signals captured by UHF sensors. These changes are due to existence of different paths for high frequency signals propagation; through those paths signal should travel to be detected by the sensors. While, the refractions and reflections coefficients are not unique in these travel paths. Hence, it is important to analyze the effects of each part of the model on propagated and recorded PD signals in these simulations. In this paper, the effects of core as a main part of the transformer structure on propagation of PDs current pulses are investigated (through related electromagnetic waves). Therefore, effect of method used for core simulation in the experimental model of transformer is evaluated. The propagation of related electric field waves is investigated by application of Finite Integration Time (FIT) method, using CST Software on this model. The calculated electric fields (by measuring probes) are analyzed with wavelet transform (WT). To select the proper mother wavelet for this study, a new approach which employs an energy scale for coefficients of each decomposition level is proposed. The results of simulations show how the different core modeling techniques (based on the position of the PD source) can affect the accuracy of measured PD signals in these simulations.