Diagnostic Testing of Power Cable Insulation For Reliable Smart Grid Operation

Polymeric insulation, especially cross-linked polyethylene (XLPE) insulated power cables are widely used in practice to transport electrical energy. XLPE has excellent dielectric properties, but its degradation due to various factors while in service is unlikely to avoid. Moreover, electrical, mechanical or thermal stresses accelerate the ageing process and shorten the lifespan. In the era of smart grid, its safe and reliable operation is vital. Hence, condition monitoring of insulation through diagnostic testing has become critically important to the smart maintenance of electrical infrastructure. In this paper, the diagnostic behaviors of XLPE insulation are explained by using two popular diagnostic methods, partial discharge (PD) and dielectric response (DR) measurements. For PD diagnosis, a comparative study of surface discharge and their characteristics under conventional power frequency (50 Hz) and very low frequency (0.1 Hz) excitation are presented. Dielectric responses are investigated in the frequency domain by $\mathrm{tan}\delta$ measurement and in the time domain by pol/depolarization current measurement. It is shown that useful information for insulation diagnosis can be extracted from the measurement results.