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This paper presents theoretical investigation of conducting particle-initiated breakdown in gas-insulated coaxial configuration under high direct voltage. The presence of contaminating conducting particles could seriously deteriorate the dielectric strength of high voltage gas-insulated substations (GIS) and gas-insulated transmission lines (GITL). This deterioration depends on the shape of the particle, the type and the pressure of the gas insulation, and the electric field. The calculated breakdown voltage initiated by particle is obtained by streamer breakdown criterion. The breakdown voltage calculation calls first for an accurate calculation of the electric field on and around the particle surface. The investigated gap is a three-dimensional field problem due to the asymmetrical space arrangement of the particle inside the gap. The particles studied are of many different shapes and sizes such as spheres, filamentary (wire) particles and fine spheres simulating the surface roughness. To solve this problem, charge simulation technique is used. The calculated field values are utilized in evaluating the breakdown voltage. The effects of varying the field nonuniformity, particle shape and size, gas type and pressure on the breakdown voltage are investigated. The calculated breakdown voltage values agree satisfactorily with those measured experimentally and with those obtained theoretically before.

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