Rotating characteristics of electric field vector in three-phase power apparatus

This paper deals with electric field characteristics under three-phase voltage in three-phase electric power apparatus such us gas insulated switchgear (GIS) and three-phase power cable. Three-phase equipment differs from single-phase equipment in two aspects: configuration and applied voltage. In this paper the effects of these differences on electric field in three-phase GIS are reported. There are periodic changes in the electric field magnitude and direction produced by three-phase voltage at any point. While the voltage phase varies, the electric field vector changes and rotates continuously. The rotating characteristics of the electric field vector in three-phase power apparatus depended on the position inside the insulation of the tank. The electric field vector locus is circular, elliptic, or linear. The elliptical nature of rotating electric field is expressed as electric field ratio. The mathematic description of the rotating electric field is given considering the maximum and the minimum electric field and the position inside the insulation. There is no zero electric field under three-phase voltage. The areal velocity of the electric field vector locus is constant. The electric field vector moves slowly in a high electric field area, but moves quickly in a low electric field area.