Influence of high frequency current transformers bandwidth on charge evaluation in partial discharge measurements

High frequency current transformers (HFCT) are now widely used for partial discharges detection and measurement, specially for partial discharge location and source identification. However, many difficulties arise due to HFCT in the determination of the apparent charge in picocoulombs (pC) because of large variations according to sensors or pulses shapes. Some authors are even using milivolts (mV) as representative magnitude. As a result, measurements carried out using HFCT are not comparable in terms of apparent charge determination. In this paper, a new method of charge evaluation by means of HFCT is described solving the calibration procedure according to the sensor bandwidth and providing a criterion for sensors evaluation.