IEC 60270 Calibration Uncertainty in Gas-Insulated Substations

Partial discharge (PD) measurements in gasinsulated substations (GIS) are tested according to the standard IEC 60270. This “conventional” PD test method applies to electrically small devices. The equipment size increases the resonance, and attenuation, contributing to the total uncertainty. Additionally, when an ultra-high frequency (UHF) sensor is used as a coupling capacitor, the calibrator and PD pulse duration difference increase the measurement uncertainty. In this paper, the IEC method, using an external capacitor coupler and a UHF sensor, is simulated and tested in a full-scale GIS. The results show the uncertainty dependency with the IEC 60270 filter bandwidth. With proper measures, the UHF sensor correlates with the external coupling capacitor, resulting in a reasonable charge estimation for a 25-meter-long GIS. Knowing the calibration limits is critical to estimate the PD charge uncertainty.