An innovative electromagnetics sensor for partial discharge detection in cable joints and terminations

The application of cross-links at the cable joints and the arrester-groundings at the cable terminals undoubtedly reduces the ground potential and the sheath current in a cable system, however, such configuration builds an open circuit in the grounding conductor and stops the partial discharges (PD) pulses to travel. Thus very few pulse energy goes into the grounding wire, which is an industrial accepted checkpoint for PD defects through conventional sensors such as high frequency current transformers. To solve the problem, this paper introduced an innovative broadband PD sensor by using a capacitive jumper to bridge the PD propagation path. In this way, the problem of impedance mismatch at PD frequency is avoided, while an `open circuit´ is maintained at power frequency. The sensor is tested in the laboratory with an oscilloscope for its sensitivity and detection bandwidth, while the latter reaches about 200 kHz ~ 87MHz. Such sensor was tested in a real 110 kV cable and shown the convenience and effectiveness in PD detection.