Study on the Detection Sensitivity and Application Limit of the DC Superimposition Method for a Water-Tree Deteriorated Cable

Abstract

In recent years, as one of the methods that permit effective and efficient maintenance of medium voltage XLPE insulated cables (CV cables), the DC superimposition method which is used to measure insulation resistance under hot-line condition has attracted attention, and efforts are being made to promote its practical application. However, there still remain some problems to be solved in applying this method.
The authors, therefore, considered the detection sensitivity of the DC superimposition method applied to a water-tree deteriorated CV cable, and examined the application limit of this method on system voltages. As a result, the following points were clarified: (1) this method can detect penetrated water-trees, (2) the upper limit of the residual insulation breakdown strength of a deteriorated cable should be considered 10kV, and (3) this method can be applied to system voltages below 6.6kV.