Partial Discharge Characteristics of Submillimeter Metal Particles on the Insulator Surface in GIS with Long-time AC Stress

The metal particle on the insulator surface is considered to be an important factor of insulator flashover. However, for metal particles on the insulator surface, the particles used in previous experiments conducted in an actual gas-insulated switchgear (GIS) are typically centimeter-scale, while research on smaller particles (smaller than 1 cm) has mainly been conducted on downsized models. Obviously, this does not match the field operational condition and cannot provide a satisfactory explanation for the actual flashover phenomenon in the field. In this paper, a high-sensitivity partial discharge (PD) measurement system was established, and the PD characteristics of submillimeter metal particles on the insulator surface of GIS with long-term AC stress was studied. The PD characteristics of submillimeter metal particles on the surface of 126kV GIS insulator were obtained under the operation voltage. The results show that with long-time AC stress, the particles on the insulator surface will gradually tend to be evenly distributed or jump to adhere to the center conductor or move to the triple junction near the center conductor and/or the grounded encloser. The PDs induced by the submillimeter metal particles on the insulator surface are sporadic and weak under operation condition, generally smaller than 1 pC. Hence, it is difficult to detect these defects effectively for the conventional pulse current method and UHF method. This paper further proves that the current PD detection methods have limitations on the detection of micro metal particles on the insulator surface in GIS.