Research on directional coupler measurement in partial discharge monitoring of XLPE cable

The cable´s partial discharge (PD) monitoring method this paper studied is the directional coupler measurement, a kind of location technology to detect the direction of the PD current in cable. This paper introduces the basic operational principle of the measurement. By imbedding a metal strip in the semi-conducting layer of XLPE cable, we could judge the PD direction through the size of the signal from the strip´s both ends. Then the structure and the equivalent circuit of the directional coupler measurement are illustrated. We simulated its working condition under power frequency and verified the principle of the method. By the theoretical analysis, the appropriate parameters were chosen and the directional coupler measurement was made in the laboratory. The experiment on the 110kV cable verified the feasibility of the direction coupler in judging the PD pulse direction.