A Modified Measurement Technique Based on the Depolarization Current Used for Power Cable

Isothermal relaxation current (IRC) method is a non-destruction evaluation method to measure the depolarization current in cable based on the dielectric response theory. In this paper, a modified IRC measurement technique is put forward to eliminate the current interference produced by test line. The equivalent circuit of XLPE cable with IRC system is built to analyze the relaxation current, and a modified measurement circuit is designed based on a method of independent measurement loop. The modified circuit can exclude the interference produced by test line from the measurement loop. By the use of the Multisim software, the difference among ideal current, current with interference and current acquired by the modified circuit is discussed, which demonstrates the feasibility and the validity of modified technique in theory. Furthermore, an IRC system is established, and a XLPE cable which has been aged thermally is detected by the IRC system. The results show that there are a lot of deep traps distributed in the aged cable insulation, which verifies the effectivity of the modified technique in practice.