Study on the Transfer Impedance of Power Cable Straight Joints

In order to assure the reliability of the power cable system, it is necessary to carry out commissioning testing after laying high-voltage cables. The distributed partial discharge detection technology in the commissioning testing can effectively expose the potential defects in the power cable system. This technology uses numerous HFCTs, high frequency current transformer to realize synchronous PD detection for power cable joints and terminals. In experiments, it was found that HFCTs connected to the ground wire of the straight-joint can not detect the discharge signal because of continuous electrical connection at the semiconductor shield layer of the straight-joint. This paper theoretically analyzes the transfer impedance of the semiconductor shield of the straight-joint by the electromagnetic theory. The characteristics of the transfer impedance of the semiconductor shield of the straight-joint demonstrates that the value of the transfer impedance is too small, the shielding effect of the semiconductor shield is so good that the partial discharge signal can not transmitte to the ground wire of the straight-joint.