直流分量电流作CV电缆老化诊断方法的现场运用探讨

Application of On-Line Diagnoses for XLPE Cables by DC Component Method to On-Site Installed Cables

介绍在实际敷设电缆时如何有效消除杂散电流以期提高直流分量电流进行ＣＶ电缆老化监测的测试精度。

The water tree diagnoses of 6. 6kV class XLPE cables by DC component method are described. This method measures the DC current component by energizing the cable with AC high voltage, therefore it would be suitable for on-line diagnoses. The DC component is considered to appear due to the rectifying effect of water trees inside the insulation.In the laboratory test, the DC component showed a good correlation with the degradation. However, almost no correlation was seen in the on-site measurement. The cause of this bad correlation found by the authors is galvanic effect inside the jacket. The jacket resistivity being low, this generates the noise current through the grounding circuit. Based on this finding, the equivalent circuit of on site measurement wes proposed.Considering the equivalent circuit, two methods were proposed to discriminate the true DC component out of noise current. One is to by-pass the noise current from the measurement apparatus, and the other is to statistically estimate the true DC component by using the transition in the jacket resistivity.The on-site test were carried out to confirm the applicability of these methods.