TRANSIENT CURRENT MEASUREMENT FOR THE DETECTION OF WATER TREE GROWTH IN POLYMERIC POWER-CABLES

In this paper, the relationship between the frequency and time domain windows is discussed. From this study an appropriate time window for t ransient current measurements may be chosen so that reliable low frequ ency dielectric data can be obtained. The suitability of applying eith er Fourier transform or the Hamon approximation for the derivation of low frequency responses is discussed for transient currents with diffe rent shapes. With water-treed LDPE samples aged in the laboratory, mea surements of transient currents, with subsequent transformation into t he frequency domain, show a loss peak at similar to 10(-4) to 10(-3) H a when moisture is retained in the samples. Even with free water remov ed, a higher dielectric loss is observed in water treed samples compar ed to virgin samples. The relaxation behavior may serve as an indicato r of water treeing in polymeric cable insulation. The results of both transient measurements and TSDC results can be affected significantly by the treatment conditions of the samples. The application of vacuum to a water treed sample can alter the activation energy of the conduct ion process and the TSDC spectra.