A feasibility study on estimating induced charge of partial discharges in transformer windings adjacent to its origin

Partial discharge (PD) measurement is a powerful tool for assessing the insulating system of power transformers. Among all the developed methods for PD monitoring, the electrical PD measurement is the only recommended method by the standard for the acceptance test of transformers due to its calibration possibility of the charge of PDs, specified as the apparent charge. However, the significant dependency of apparent charges to the location of the PDs inside the transformer winding makes the defining a proper threshold value as an accepted PD level a demanding task. In this contribution, the feasibility of a new method to estimate the charge of the PD at its origin in the winding has been studied. The proposed method reconstructs the original current of PD in a limited bandwidth using PD signals measured at terminals of a transformer along with the sectional winding transfer functions and the input impedance of the winding. The original charge of PD will be determined from its reconstructed original currents. This charge value can provide a more robust threshold value for the PD acceptance test as well as a better evaluation of the severity of PD. According to the proposed method results, the estimated charge values are in the range of 0.26–1.88 of the original charge of PD, while the apparent charge values could be 0.02 of the original charge value in the IEC standard method.