New partial discharge detection method for live UHV/EHV cable joints

Partial discharge (PD) detection for live UHV/EHV power cables and accessories is the most important test on cable systems, to prevent problems caused by minor mistakes in jointing the cable. A new PD detecting method is proposed. A REDI (resonance type partial discharge) sensor was developed for detecting PD occurring inside the joints of live XLPE insulated cables. This sensor picks up the high frequency components of a PD pulse in the noiseless range (for example, for 10 to 50 MHz). This new method was employed to observe the initial AC breakdown tests applied to three different types of joints used in UHV/EHV power cables. PD pulse sequences were observed just before the breakdown in all cases. A PD pulse sequence against the phase of applied voltage (A γ-q characteristic) changed with time or degree of deterioration of the sample. Results of these experiments show that a REDI sensor can be used for insulation diagnosis of live power cable joints