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Dielectric response study of service-aged XLPE cable based on polarisation and depolarisation current method

Dielectric response measurement based on the polarisation and depolarisation current (PDC) method is a diagnostic tool commonly employed to the insulation condition assessment of power apparatus. In this paper, experimental studies are carried out on short sections of service-aged XLPE cable. Daniel's normalisation is applied to estimate the difference between the permittivity under DC excitation and that at optical frequency. Physical explanations of various polarisation processes at low and high frequencies are interpreted through the clustering model. Based on transforming the PDC currents into the frequency domain equivalents, dissipation/loss factor (tan δ) measurement and modeling over the range of frequency from very low to power frequency are presented. The analysis reveals the relationship between individual loss factors and the overall loss factor. Also, measurements of the activation energy and testing under varying electrical stresses and ambient conditions provide further information for interpretation.