A Modified Three-Phase Synchronous Isothermal Relaxation Current Detection System Based on Independent Measurement Loop Method

As a nondestructive testing technique, the isothermal relaxation current (IRC) method has been applied to assess the condition of power cable insulation. In order to shorten the detection time in the field and improve the measurement accuracy, a modified measurement circuit based on an independent measurement loop was proposed to discharge the interference from the high-voltage insulated wires. Based on this circuit, the three-phase synchronous IRC measurement system was established. Furthermore, the independence and consistency of the three-phase current measurement loop were verified, which could realize the synchronous acquisition of the three-phase relaxation current. Finally, the three-phase IRC test was carried out to evaluate the aging state of the sample in service. The results showed that the aging state of each phase for the same cable might be quite different after long service.