Performance of Gas Insulated Substations with Metallic Particle Contamination under the Influence of Various Types of Voltages

Compressed gas insulated substations (GIS) consist basically of a conductor supported on insulators inside an enclosure, which is filled with sulfur hexafluoride gas (SF₆). The voltage withstand capability of SF₆ bus duct is strongly dependent on field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. The particles can be lifted by the electric field and migrate to the conductor or insulators where they initiate breakdown at voltages significantly below the insulation characteristics of the SF₆ gas. In this paper for optimized design of GIS by changing the inner and outer diameter to 40 mm and 137 mm is considered for analysis and compared with a single phase enclosure with outer diameter as 152 mm and inner conductor diameter of 55 mm with aluminum, copper and silver particles of size 10 mm in length and 0.25 as radius present on the enclosure. Very often, the operation of electrical equipment may seem normal, but under a certain combination of conditions, the impact of harmonics is enhanced, with damaging results. To study the behavior of metallic particles in the presence of harmonics different types of input voltage waveforms like square, triangular and asymmetric sine wave are applied to single-phase gas insulated busduct. The maximum movement of aluminum, copper and silver particles for applied voltages of 75 kV 100 kV, 132 kV, 145 kV, and 200 kV for triangular, square and asymmetric sine wave are determined. The results have been presented and analyzed.

I. Introduction

SULPHUR hexafluoride is the electric power industry's preferred gas for electrical insulation and, especially, for arc quenching current interruption equipment used in the transmission and distribution of electrical energy. Compressed Gas Insulated Substations (GIS) and Transmission Lines (CGIT) consist basically of a conductor supported on insulator inside an enclosure, which is filled with SF6 gas. As one is aware of the attractive features of a Gas Insulated Substation (GIS), they also suffer from certain drawbacks. One of them is the outage due to seemingly innocuous conducting particles, which accounts for nearly 50% of the GIS failures. The contaminants can be produced by abrasion between components during assembly or operations. Flash over in a GIS is, in general, associated with longer outage times and greater costs than in a conventional air insulated substation. A conducting particle can short-circuit a part of the insulation distance, and thereby initiate a breakdown, especially if electrostatic forces cause the particle to bounce into the high field region near the high voltage conductor.