PURPOSE: To make the device not subjected to the influence of metallic foreign matter and reduce the size by specifying the inside diameters of the horizontal part and the vertical parts of the metallic container constituting a gas insulating switch and the outside diameter dimension of the high voltage conductor on the inside of it under specified conditions.

CONSTITUTION: A horizontal tank 3 with an inside diameter of R1 charged with insulating gas and a vertical tank 5 with an inside diameter of R3 are connected in the shape of two L's as shown in the figure. High-voltage conductors 4 and 6 with outside diameters of R2 and R4, respectively, are stored inside the tanks 3 and 5, respectively, thus they constitute a horizontal bus 1 and a vertical bus 2, respectively. The relation between the dimensions R1-R4 and the voltage is specified as the condition formulas 1-3 in the figure. But, VACKV = the normal grounding operation voltage of the system applied to the conductor 4. VIMPKV = the impulse-resistant voltage of the system applied to the conductor 6. EC=the tolerable electric field value on the surface of the conductor 6 being decided by the pressure of the SF6 gas charged in the metallic container. Hereby, the tank 3 being subjected to the influence of the residual metallic foreign matter inside the metallic container and the tank 5 not being subjected to it are divided definitely, and the design is optimized, and the device becomes compact.