Takanori Yasuoka

Influence of tiny metal particles on charge accumulation phenomena of GIS model spacer in high-pressure SF 6 gas

The charge density distribution of the downsized GIS disc spacer made of epoxy resin was measured in 0.5-MPa (abs.) SF6 gas. A dc voltage was applied to the spacer, and the charge density on the surface was measured using an electrostatic probe. Voltage application and charge measurement were conducted in a sealed chamber without opening it. After the voltage application of 60 kV, radial charge patterns appeared on the spacer. Tiny metal particles whose size is smaller than 0.1 mm were observed on the spacer after the voltage application. Metal particles on the spacer may cause the radial charge accumulation in this experiment: if a metal particle adheres on the spacer, partial discharge may occur near the metal particles and negative charges may progress along the surface of the spacer.

Forces affecting metallic particle motion in GIS

The bounce height of a metallic particle in Gas Insulated Switchgear (GIS) is one of the key factors which affect GIS reliability. Simulation of particle motion can evaluate bounce height if the relevant forces acting on the particle are taken into account. This paper presents an approach to simulating particle trajectories including dipolar force and drag force from SF6 viscosity. The influence of various forces is evaluated through the comparison between the simulation results and particle trajectories determined from high speed camera observation of particle motion.

Computation of particle motion in gas-filled systems

The force on a particle in a gas-insulated system is considered in two contexts, viz., (i) the force caused by a field gradient at a conductor surface and (ii) the forces (torques) that drive “firefly” motion at a conductor. These two problems have a degree of commonality, as demonstrated in the mathematics.

Computation of horizontal force normal to the axis of a spheroidal conducting particle in a field gradient

When a cylindrical or spheroidal conducting particle resides in an electric field which is quasi-homogeneous over the axis of symmetry of the particle but inhomogeneous in the direction normal to the particle, the particle is subject to a force normal to its axis in the direction of the field gradient. In the 1980s, Cooke treated this problem experimentally, based on an expression for the force in terms of an empirical constant times the product of the field times the derivative of the electric field a direction normal to the particle axis. The present contribution provides a general analytical expression this force which agrees with that determined by Cooke for his experimental configuration.

Approximate formula of electrostatic force on spheroidal particle between coaxial electrodes

An existence of an electrostatic force which draws the particle in the direction of increasing field was indicated by FEM analysis. An approximate formula of the electrostatic force was derived analytically and compared with the results of FEM analysis. This force is sufficiently large to be relevant to particle motion in gas insulated switchgear.