Polarization and Depolarization Current Measurement for Foreign Object Detection in Gas-Insulated Transmission Line

Polarization and depolarization current (PDC) test is one of non-destructive insulation test method that usually uses for diagnosis the solid and liquid insulation problems. In case of gas-insulated transmission line (GIL), it not only comprises of gas insulation but also the solid insulation such as cone insulators. This paper presents the PDC measurement for foreign object detection in GIL. A 230kV, 2500A, single phase GIL with 2 m length was used in the PDC experiments. The external diameter of this GIL conductor and enclosure are 92 and 366 mm respectively. In the experiment, defects on the cone insulator was simulated in three cases, i.e. 1) cone insulator was attached with a paper tape, 2) cone insulator was attached with an aluminum foil, 3) cone insulator was attached with a moist paper. The width of the simulation defect was approximately 2 mm. The lengths of the simulation defects were varied from 25 – 200 mm depending on defect types. PDC test results obtained from the GIL with the simulated defect cone insulators were compared with that of clean and dry cone insulator as reference. The results of the experiments showed that PDC curves obtained from GIL with the simulated defect cone insulators were clearly different from that of the reference case. Other analyses are reported in the paper.