A Comparative Study of Dielectric Dissipation Factor Measurement under Very Low and Power Frequencies

Very low frequency (VLF) high voltage testing had been used as a simple withstand test (go/no-go). Recently, VLF diagnostic testing has emerged as a promising tool for insulation assessment of power cables. The term VLF implies testing insulation with an excitation voltage at frequency of 0.1 Hz or lower. In this paper, a comparative analysis of the dielectric dissipation factor (DDF) or tan delta measurement is presented for 11-kV cross-linked polyethylene (XLPE) cable at power frequency (50 Hz) and at VLF. Here, the DDF response is measured from frequency 50 Hz to 0.1 Hz for four short cable sections where each sample has a capacitance lower than 300 pF. The experimental results show that the DDF value at 0.1 Hz is much higher than that at 50 Hz. Furthermore, differential tangent delta (DTD) and correlation of DDF values are calculated to incorporate with experimental results.