Research of Dielectric spectroscopy on insulation ageing assessment of XLPE cables

In this paper, the model cables are studied by means of frequency domain spectroscopy (FDS) which involves the measurement of capacitance, the real permittivity and dissipation factor as a function of frequency. Firstly, XLPE cable samples were carried out accelerated thermal ageing at 135 °C. Then, frequency domain spectroscopy was investigated under laboratory condition, including different degree of thermal ageing and different test temperatures. Mechanism was analyzed using the theory of dielectric relaxation in solids. From the data and curves, it can be shown that the capacitance and dissipation factor are increased with the ageing time, and dissipation factor is increased with the decreasing of frequency in specific frequency range. Moreover, capacitance and real part of permittivity were found to be more sensitive to temperature variation, thus temperature is a key factor which must be taken account when using FDS method for diagnosing cable insulation. The investigation of dielectric spectroscopy is effective and convenient for ageing assessment of XLPE cables.