Partial Discharge Properties in XLPE Block Sample with Electric Tree Defect and Difference in Charge of PD Properties Observed between IEC60270 and the UHF Method

XLPE power cables are widely used in the transmission and distribution network and required high reliability for the stable and safety operation in the power system. This paper described partial discharge properties of XLPE block sample with a needle stuck defect, which eventually initiated electric tree by applying ac high voltage, measured with two methods: one is a conventional method followed by IEC60270 standard (IEC method) and the other is the UHF method to measure the emitted electromagnetic waves. In the IEC method, the authors have used PD measurement systems (OMICRON, MPD600) and measured the signals through a high-frequency current transformer, CT, a coupling capacitor unit, CC and an HA antenna with a UHF unit. Applying the system, the phase-resolved PD pattern, and its time change pattern for the XLPE samples were observed. In the UHF method, we used the HA antenna and a MA antenna, and a digital oscilloscope. Using the fast flame function of the oscilloscope, we observed the time change of PD-emitted electromagnetic waves together with the IEC method measurement. As a result, in the IEC method, the observed signals by the CC and CT were identical in PD pattern and the intensity, and their properties changed depending on the sample condition even in the tree initiation condition. However, the remarkable change was not found during the developing tree condition. To investigate this property further, we investigated the properties by the UHF method and compared them together with the PD current waveform measurement. Based on the PD current properties, the advantage of the UHF method and problem of the IEC method were discussed so as to evaluate the PD properties even in the developing tree condition.