공간전하 측정용 펄스발생기의 개발과 응용

Development and Application of Pulse Generator for ^pace Charge Measurement

Water tree has been considered to be very harmful for underground power cable insulation. To understand the electrical characteristics of water tree degraded XLPE, artificially aged XLPE specimens of which the water tree with uniform leghth grew on the large area have been fabricated. The AC breakdown strength of the water tree aged specimens has been reduces as the growth length increased and the trend of reduction has been similar to that of water tree growth rate. Space chage distributions in the virgin and aged specimens have been measured by the PEA method and, as the results, it has been shown that the homo-charge is heavily concentrated at the tip of the water tree path while a little hetero-charge is gathered in front of electrode contacted to the water tree. Through the electric field calculation using the charge distribution, the local field enhancement at the tip of water tree path was also verified. Based on the experimental results and analysis, it can be said that the water tree reduce the breakdown strength of XLPE because of the homo-charge concentration at the tip of water tree path, which results in the reduction of effective insulating thickness.