抄録
This paper describes the water tree diagnoses of 6.6 kV class XLPE cables by DC component method. The DC current component is measured 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 authors found that the cause of this bad correlation is galvanic effect inside the jacket. This generates the noise current through the grounding circuit when the jacket resistivity is low. Based on this finding, the equivalent circuit of on-site measurement was proposed.
Considering the equivalent circuit, this paper proposes 9 methods for discriminating the DC component due to water tree from noise current. And, this paper describes the analytical results of each method. Furthermore, the on-site or laboratory tests show some of them are effective to separate the DC component due to water tree from noise current.
