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 cross-linked polyethylene (XLPE) cable insulation by investigating dielectric relaxation current (DRC). 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 analyzed 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 RFD, 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 m.c. by empirical relationships. Finally, another set of laboratory-prepared XLPE cable samples with a known m.c. 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 m.c. of the XLPE cable insulation in power system network applications.