Investigation of Complex Permittivity of XLPO Insulated Photovoltaic DC Cables Due to Thermal Aging

Abstract

To study the effect of thermal aging on the low voltage DC cables used in photovoltaic systems, XLPO based cable samples were thermally aged for four different cycles of 240, 480, 720 and 960 h at 120 ℃. This aging time was equivalent to 20, 40, 60 and 80 years of service period at 60 ℃. The dielectric properties, real and imaginary part of permittivity were investigated for a frequency range of 20 Hz to 500 kHz using impedance analyzer. The polarization and leakage current effects have been discussed due to the thermal aging. The results show that the real part of permittivity increased with the aging due to the creation of dipoles because of the morphological changes happening inside the material. While the imaginary part of permittivity decreased at low frequencies and increased at higher frequencies. Also, there has been shifting of minimum value of imaginary part of permittivity to lower frequency, 500 Hz from 2 kHz with aging, showing that the resistance of the material increased at low frequency and the material becomes stiffer and hence an end-of-point to the degradation of insulation material has reached.