Application of Distributed Partial Discharge Detection in Sync Technique to After-laying Withstand Voltage Test for Large-scale 500kV XLPE Cable Circuit

Partial discharge (PD) detection in withstand voltage test is different from that under operation voltage for after-laying cable circuit. For large-scale XLPE cable circuit of 15km, a special distributed PD detection in-sync testing system was created for the withstand voltage test of 500kV (1.7Uo/1Hr), HFCT PD sensors were distributed and installed at every cable joint and cable termination. To localize a PD where and when it is just detected between any two neighboring PD sensors on a cable, all local signal process units are made to work synchronously, and the communication system is constructed by optical fiber cable. To ensure the high quality examination, measurement of PD propagation velocity of cable, frequency characteristics, and calibration with injection by PD simulated pulse generator were conducted onsite before test. This paper also shows some print-screen photos from the practical test to tell how the corona and the other background noise signals can be distinguished by the detected original signal waveform, selecting detection frequency filters, and the time differential identification unit. It should be a valuable reference case.