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The phenomenon of accumulated charges on solid insulator surfaces is one of the critical parameters to consider at the insulation design stage, for ac electric power equipment as well as for dc equipment, so it is important to investigate the characteristics and predominant factors underlying various charging mechanisms. Several researches related to this theme have been reported, but independently, and cross-sectional comparison and evaluation from a unified viewpoint are meaningful. In this paper, the resistance of solid insulator is first discussed, showing that the resistances found by diverse measurements are in a fairly good agreement under similar conditions of the temperature and electric field. Next, three kinds of electric charging mechanisms, i.e. volume conduction, surface conduction and electric field emission are characterized in terms of the time constant, applied voltage and charge distribution. Then, eight cases of recent measurements on the charging time are investigated and their charging mechanisms are classified. Electric field emissions are likely to occur with model spacers made in routine GIS manufacturing process at the electric field level used. Further, three examples in cases with metallic particles are introduced, of simulating charge from edge on the tank, spacer surface charging phenomena, and influence of charge on spacer surface flashover. It is expected that this paper will be helpful for understanding charging phenomena e.g. on insulation spacers in gas insulated switchgears. [ABSTRACT FROM AUTHOR]

This paper deals with the breakdown voltage characteristics of saturated liquid helium in the presence of a needle-shaped or spherical metallic particle to obtain insulation design data for pool-cooled, low-temperature superconducting coils and to find the predominant factor affecting the breakdown voltage of liquid helium at a given state. The results show the following. (1) The generation of bubbles at the instant of collision of a particle with an electrode is caused mainly by the kinetic energy released from the moving particle to the liquid helium, while the electrostatic energy accompanying the microdischarge between the particle and the electrode has a lesser effect on it. (2) The lowest breakdown voltage at different particle conditions appears in the case of a free needle particle. The low breakdown voltage is caused by the bubble triggered by the particle collision, the high electric field at the tip of the needle particle, and the rich initial electrons supplied by the microdischarge. [ABSTRACT FROM AUTHOR]

The force acting upon a free metallic particle in an alternating electric field will determine its motion and ultimately allow for the estimation of the risk imposed due to dielectric failure of the high voltage equipment. Existing models approximate the force with Lorentz' law and consider the charge resting upon the surface as being lumped into a point charge at the center of the particle during its motion. The model proposed in this paper demonstrates a time stepped electrostatic Finite Element Method to calculate these forces, therefore taking into account the charge distribution upon the surface of the particle. The use of this model is seen to have a significant effect upon the motion of the particle under certain conditions. [ABSTRACT FROM AUTHOR]