Challenges in calibration of the measurement of partial discharges at ultrahigh frequencies in power transformers

The detection and measurement of partial discharge (PD) is a well-known method for evaluating the insulation performance of power transformers. According to the IEC 60270 standard, the apparent charge is measured in a frequency range below 1 MHz using an electrical circuit which quantifies only a portion of the discharge energy conducted to the PD detector through the conductors. However, it is also well known that the PD energy is not only conducted but also transmitted via electromagnetic (EM) and optic waves, acoustic waves, and thermal energy. This article describes the significant challenges and the problem of calibrating the ultrahigh frequency partial discharge measurement method for power transformers and clarifies the complexities theoretically and experimentally.