Partial Discharge Current Analysis in a 6.6 kV Cast Resin Transformer Using High Frequency Equivalent Circuit Calculation

This paper presents a high-frequency equivalent circuit model applicable for partial discharge (PD) location in an inductive test of a 6.6 kV-VT cast resin transformer (CRTr), in which a voltage is applied between the high-voltage terminals. Proposed equivalent circuit consists of the winding inductance, and the capacitance between adjacent inter-windings and that between the winding and ground of CRTr. The proposed circuit allows to simulate PD phenomena occurring in the windings. The estimation of the dominant frequency f
r
for PD detection can be achieved through the frequency characteristics of the impedance Z(f) measurement of CRTr and the calculation of its high-frequency equivalent circuit. This allows for the identification of PD and noise in the field, leading to improved defect detection sensitivity. Measurements of PD current waveforms were also made in a 6.6 kV VT with the inductive test circuit. Measured results were compared with waveforms calculated using the equivalent circuit. As a result, it was found that the polarity of the rising part of the current and dominant frequency components of simulated PD current waveforms were almost consistent with experimental ones.