Noise discrimination from PD signal in pre-breakdown discharge detection test

In Japan, 22-77 kV cross-linked polyethylene (XLPE) cables have been put into practical use for about 40 years, and some of them have been in operation for more than 30 years, which exceeds their expected lifespans of 30 years. At these voltage levels, the degradation of the insulation of XLPE cables is due mainly to the water tree. Central Research Institute of Electric Power Industry (CRIEPI) has studied the dielectric strength of XLPE cables and the various aspects of water tree degradation using a pre-breakdown discharge detection (PBPD test). This test´s success rate of whether to find the water tree of weakest point in cable specimen depends on a method that distinguishes small partial discharge (PD) signals caused by water trees from noises in noisy environments of the test field. It also determines the likelihood of establishing a robust PBPD test that incorporates the developed method for the discrimination of PD signals from noises.