Underground power cable diagnostics: Online defect positioning

Underground power cables are increasingly employed to transfer electricity. In the Netherlands, all medium-voltage (MV) and low-voltage (LV) networks are realized with underground power cables. Consequently, power cable diagnostic has became a relevant subject. An online defect positioning technique is proposed based on characteristic impedance variations, which usually occur in the power cable at the defect position. To this end, the cable impedance is monitored at a ring-main-unit (RMU) with the help of online impedance measurement technique. The measurement utilizes a bulk current injection probe (BCIP) clamped around the earth wire inside the RMU. The frequency domain impedance is transferred into the time domain impulse response by applying the inverse discrete Fourier transform (IDFT). Thus, the frequency domain impedance variation can be observed in time domain which includes the defect position information.