Particle-initiated corona and breakdown in GITL systems

Abstract

The paper deals with partial discharges caused by metallic contaminants in gas insulated transmission line (GITL) systems. Investigations were made on discharge characteristics in compressed sulphur hexafluoride (SF6) with free aluminum particles under AC voltage in a 70 mm/190 mm coaxial conductor system. Corona inception voltage, together with the time to first corona, are introduced asa possible diagnostic tool in estimating the size of the conducting particles present in the system.

Investigation of gas pressure on metallic particle contaminationin 1-Ø gas insulated busduct

“…Such particles move randomly in the inter-electrode gap and the motion trajectory dependsonthe particle shape, size and material, gas pressure and nature of the applied electric field [4].The higher the movement of these particles, the higher is the probability of the system for breakdown as these particles become hazardous to the system operation. Generally, the conducting particles encountered in practical GITL systems are filamentary in shape [5].The schematic diagram of a typical compressed Gas insulated busduct is shown in Fig.1. The understanding of the dynamics of a metallic particle in a coaxial electrode system is of vital importance for improving the voltage withstand capacity of a Gas Insulated System [2].The probability of these conducting particles, crossing the gap and causing the flashover can be estimated if the metallic particle's motion pattern is determined.…”

Corona characteristics for free conducting particles in various SF/sub 6/-gas mixtures

“…Generally as expected, corona onset voltage decreases as 1 is increased or as q5 is decreased. For coaxial geometry, it has been shown earlier in [18] that a three fold increase of the length of wire particles, decreases the corona inception voltage only by M 13%. The present results show that there is a relatively large difference of 20 kV between the onset voltages for parallel-plane and concave electrodes which clearly points out the significance of the macroscopic field distribution in the gap.…”

Motion of metallic particles in gas insulated systems

“…Some authors suggest that the particle loses its entire net charge as discharges from the particle occur [24]. Since this situation is relatively easy to implement, two conditions were included (one for each end of the particle) in the motion equation in order to account for the possibility that the particle may change its charge due to discharges.…”