Experiments on Vacuum Interrupters in High Voltage 72KV Circuits

Three experimental 23cm diameter vacuum interrupters have been built and their performance has been evaluated in single-phase, high-voltage, high-current circuits. The first of these experimental designs contained 11.7 cm diameter, spiral electrodes and one floating arc shield. It interrupted bus circuits up to 42kV (72kV x 0.58)/l5kA. The second and third prototype designs contained three floating arc shields. Prototype number 2, equipped with 14cm diameter, spiral electrodes, passed single phase bus fault tests at 42kV/40KA and 63kV(72kV x 0.87)/3OkA. The third prototype, designed to ensure that a diffuse vacuum arc could be maintained at very high currents, interrupted bus fault currents in the range of 4OkA to 6OkA in a 63kV circuit. This design also showed potential for series operation at 145kV/55kA for both bus and short line fault situations. Test data are presented in this paper and are discussed with respect to electrode diameter, the contact gap at current zero and the need for maintaining a diffuse vacuum arc.