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.