Experience of Partial Discharge with IEC Type Testing and after Installation Testing for extruded Cables

摘要

Partial Discharge (PD) measurement methods are most important and preferred in testing of underground high voltage cables and they have received much attention in recent years. Apparent charge, partial discharge inception voltage as well as number and distribution of PD pulses are most important quantities for the determination of the insulation quality. This paper described experiences of PD measurements with AC resonant voltages in Extra High Voltage Research Centre (EHVRC) laboratory according to IEC standards and after installation test of installed XLPE HV and EHV single core underground cable systems. The paper outlines the difference between PD measurements performed on individual components in the laboratory and PD measurements performed on installed systems in the after installation with respect to magnitude calibration of PD pulses. Fact is that all the power cables are tested in the laboratory with the best methods and with calibrated PD measuring systems in the shielded room with high sensitivity; as a result the background noise level is less than 2 pC. A general principle of the insulation co-ordination and HV testing is that the applied test voltage simulates the stresses which occur during the operation of the HV apparatus. Successful measurements give fingerprint for further diagnostics during the service of the cable system. Tell now for after installation test, PD measurements are actually not required by IEC 60840 &IEC 62067, but the testing experience more than 12 years shows a population of extrude cable systems subjected to a combination of AC testing and PD measuring acceptance testing. This paper summarizes the experiences of on-site testing and the obtained results are compared with the IEC type tests. One important conclusion of this paper is modifications of IEC 60840 & IEC 62067 are required to evaluate the on-site after installation testing for extruded cables.