Discussion on Partial Discharge Measurement Technique of Cable Joint in Three Phase High Voltage Overhead Transmission Line

Cable joint in high voltage overhead transmission line connecting a pole transformer is one of the important accessories. Reliable diagnostic technique for possible insulation failures in cable joint due to the long-term operation and aging is required. The purpose of this research is to establish the insulation diagnostic technique for the cable joint by measuring partial discharge (PD), which is a precursor phenomenon of dielectric breakdown. In this paper, PD signals in three-phase high voltage overhead transmission lines with 6.6 kV cable joints, actually used in electric power company, were measured by using various sensors, i.e., high frequency current transformer (HFCT), monopole antenna, and transient earth voltage (TEV) sensor. As a result, it is shown that HFCT shows the highest sensitivity for PD detection among three kinds of sensors. It is also shown that the arrival time difference of the PD signals detected by several HFCTs enables to determine the PD source in neighboring two utility poles. Furthermore, the intensity and the polarity of first arrival part of the PD signals detected by several HFCTs enable to determine the PD source in a particular cable joint among the three ones in a utility pole.