Partial discharge coefficient calibration and charge estimation using high-frequency current transformers

Accurate estimation of apparent charge is essential for reliable partial discharge (PD) diagnostics. The limited bandwidth and non-ideal frequency response of high-frequency current transformers (HFCTs) introduce measurement errors that require calibration. This study investigates a calibration approach for HFCT-based PD measurement that employs a capacitive charge-injection technique. An analytical

review is conducted to describe the charge transfer mechanism and to define calibration conditions. The proposed approach determines correction coefficients by comparing the known injected charge with the charge obtained from numerical integration of the HFCT output voltage. Four HFCT sensors with different bandwidths and terminating resistances are experimentally evaluated using a dedicated calibration setup. The results demonstrate that wideband HFCTs reproduce the injected pulse with high consistency, whereas narrowband sensors exhibit waveform distortion and integration errors due to their limited frequency response. The study further quantifies the trade-off between measurement sensitivity and bandwidth with the selection of burden resistance. The proposed calibration approach provides a practical framework for improving the reliability and consistency of HFCT-based partial discharge measurements.