Detection of Partial Discharge and Investigation for AC 22.9kV Power Cable Termination

The measurement of PD(Partial Discharge) plays a major role in the assessment of the cable system's condition. The PD test applied to the power cable system is generally performed in short-term. However, since PD has physical characteristics of irregularly repeating occurrence and extinction, there is a possibility that even if a PD test is applied to a defective cable system, it cannot be detected. Therefore, the long-term PD test is necessary. In this work, on-load PD measurement was performed at AC 22.9kV power cable terminations. PD was measured on the high frequency band using inductive sensor attached on termination, and monitored for 14days. The result shows that PD was measured at one of the measurement points, and it was observed that occurrence and extinction were repeated irregularly. To verify the PD test result, X-ray test was taken and internal defect was found. After those non-destructive inspections, dismantlement of termination was performed and the exact coincided with the result of PD test. Based on this result, this PD measurement and analysis could be effective solution to assess condition of cable termination.

I. Introduction

The reliability of the electrical power transmission and distribution is mostly affected by the reliability of operating power cable system. The stable operation of the HV cable system relies on the quality of the insulation material of cable because it has to withstand a high electric field during operation. PD(Partial Discharge) measurement is one of the important and advanced technologies to measure the insulation quality of a power cable. If a defect exists in the cable insulating layer, an electric field distortion may occur, and cause Partial Discharge.[1] In addition, if PD is continuously occurred, it can be developed to the electric tree and cause insulation breakdown. In general, PD measurement at on-site are performed with short-term test. However, PD has physical characteristics of irregularly repeating occurrence and extinction. Therefore, even if there's a defective insulation layer of a cable, PD could not be detected in case of using short-term(1∼2hours) test.