Three position switch based on vacuum interrupter technology suitable for disconnecting and earthing purposes

Three position switches are mostly used in SF₆ switchgear. A new three position switch is proposed based on vacuum technology to fully employ the superb dielectric performance of vacuum with regard to a compact design. The proposed "Three Position Switch" (TPS) provides the same functions as known from existing switchgear, such as disconnecting, isolating in a middle position and earthing. The design is rated to 24 kV- 25 kA-1250 A-50/60 Hz. Switchgear equipped with the new TPS can be very compact. The TPS fulfils the electrical and mechanical requirements specified in the corresponding 1EC standards. The dielectric properties are described with emphasis on electrical field calculations in comparison with high voltage tests on samples. The short time withstand current was proved up to 3 seconds with applied contact force in connected and earthed position.