Relaxation Frequency Distribution Based Approach Toward Moisture Estimation of 11 kV XLPE Cable Insulation

This article presents an advanced diagnostic technique to estimate the moisture content (m.c.) in the XLPE cable insulation by investigating dielectric relaxation current. For this purpose, the experimentation is carried out on the short-section of the moisture injected XLPE cables. The relaxation characteristics of the XLPE cable insulation are analysed using the relaxation frequency distribution (RFD) function. The RFD function reveals the relaxation phenomenon of the XLPE cable and correlates with the clustering model. Based on the relaxation frequency distribution, five moisture sensitive parameters (i.e. two relaxation peaks, their ratio and corresponding relaxation frequencies) are identified. These five moisture sensitive parameters are correlated with moisture content by empirical relationships. Finally, another set of laboratory prepared XLPE cable samples with a known moisture content are used for experimentally validating the proposed technique. This experimental investigation illustrates that, the relaxation frequency corresponding to the highest peak of the RFD function can reliably be used for estimating the moisture content of the XLPE cable insulation in power system network application.