The condition assessment system of XLPE cables using the isothermal relaxation current technique

The isothermal relaxation current (IRC) technology is a powerful method for assessing the condition of power cable insulation. In this paper a condition assessment system was designed to meet the diagnosis of XLPE cables insulation. The assessment system consisted of the IRC measurement system and IRC analysis system. The processes of IRC measurement, such as polarizing voltage, discharging and depolarization current measurement, were controlled by software. The third order exponential decay model was utilized in analysis software to process measured IRC data. The parameters of each kind of depolarization current component and the relationship between I*t and log (t) were showed directly in software for evaluating the aging status. Based on the empirical aging factor (A-factor), the aging level of cables insulation is obtained after data analysis. At last, one part of three-phase AC XLPE cable was measured used this system. The result shows that the system is precise and the diagnostic criteria of A-factor should be corrected to meet the XLPE cable made in China.