A Method for Analysis of DC Partial Discharge Measurement Data from Cable Joints

Partial discharge (PD) measurements under DC test voltages are a challenging task. The high insulation resistance leads to low repetition rates of internal PD. Furthermore, the inception voltage is higher as compared to AC and the magnitude of the discharges is lower. Unfortunately, electro-magnetic background noise and interferences will also be picked up by the highly sensitive measurement equipment. Commonly noise is misinterpreted as partial discharge. Approaches to solve this problem are usually based on applying statistical measures or analyzing the shape of pulse waveforms. While the first approach can be effective in cases where the repetition rate is high (e.g., in gas-insulated gear) the second approach usually requires recording and analyzing large amounts of data from long measurement durations in post-processing. Neither approach has been applicable in our case. The authors therefore present an approach of pulse polarity and tolerance filtering for partial discharge measurements on cable joints. Results of the application on real measurement data from a ±535 kV HVDC cable system are presented and discussed.