XLPE 지중케이블에서 부분방전의 측정과 분석

Abstract

This thesis dealt with the characteristics of partial discharge (PD) depending on defect and the defect localization in an XLPE underground cable. Four types of defects with different sizes and positions were fabricated inside a cable of 1m long and 60mm2. A 50kV transformer was used to apply high voltage to the cable for generating PD. The discharge pulses were detected by a high frequency current transformer(HFCT) with a frequency range of 150kHz-30MHz, and acquired using an oscilloscope(5GS/s) and a data acquisition unit. The PD characteristics were analyzed in terms of discharge inception voltage (DIV), apparent charge, and phase-resolved partial discharge(PRPD) pattern developed by a LabVIEW program.

From the results, it showed that the DIV increased with the size of defect and the apparent charge increased as the defect was adjacent to the conductor. In four types of defects, the PRPD presented similar phase distribution. However, it was indicated that the pulse count in the negative half of the applied voltage became higher as the defect got closer to the conductor.

The defect localization experiment was conducted based on the time-domain reflectometry method using the PD pulse. The HFCT was set at 1m from the near end of the cable, where the measurement point was selected. To verify the validity of this method, cables with different lengths and defect positions were used. The time interval between the PD pulse and the reflected pulse was measured as 474ns for the 50m cable with defect at 2 m from the near end. And the time intervals for the 70m cable with defect at 2 m and the 50m cable with defect at 30m were 690ns and 208ns, respectively. It was revealed that the proposed method can localize the defect in a cable with an error less than 1m.