Metallic Particle Motion and Breakdown Characteristics in GIS with 0.1Hz VLF (Very Low Frequency) High Voltage Application

Abstract

VLF (Very Low Frequency) high voltage with frequency of 0.1Hz will be utilized for an on-site test of XLPE underground cables, instead of conventional dc high voltage test. Since XLPE cables are connected to GIS (Gas Insulated Switchgears) in substations, the influence of VLF voltage application to GIS insulation should be investigated. One of the most important characteristics for GIS insulation lies in the metallic particle contamination and its behavior, which may induce breakdown in GIS.
From the above viewpoint, this paper discusses the metallic particle behavior and breakdown characteristics under VLF voltage application in GIS. Experimental results revealed that (1) Particle motion under VLF condition was similar to that under dc condition, while specific in the transient behavior at the polarity reversal. (2) Breakdown was induced by particles located in the vicinity of high voltage conductor at the instance of crossing the gap or in the firefly conditions. (3) Breakdown voltage in positive half cycle was higher than that in negative half cycle at the lower gas pressure, while lower at the higher gas pressure, which was attributed to the particle behavior and the breakdown mechanism of SF₆ gas.
Consequently, metallic particles in GIS under VLF voltage application exhibited the specific behavior associated with the slow change of instantaneous voltage and polarity, and resulted in the complex pressure dependence of breakdown characteristics.