Vacuum switchgear for fusion experiments

Abstract

Fusion experiments frequently have demanding switching requirements that cannot be satisfied by conventional switchgear. Two frequent requirements and specialized vacuum switches designed to meet them are presented. Experimental results from testing of prototype devices are discussed. A frequently encountered switch application is the interruption of a high level, pulsed, dc current followed by a fast rising recovery voltage. A 7-in. vacuum interrupter with an axial magnetic field has proven to be an effective switch for currents up to 25 kA. Beyond 25 kA, a parallel configuration becomes necessary. The influence of the axial magnetic field on the behavior of parallel vacuum interrupters and test results up to 50 kA are discussed. Also, test results on experimental devices with novel electrode geometries such as the rod-array vacuum interrupter and the Amsler contact interrupter are presented. Interrupters which can carry large dc currents on a continuous basis are frequently required in fusion applications. This requirement occurs in superconducting coil protection circuits and generally involves recovery voltages of 5 kV or less. A specially designed vacuum interrupter with water-cooled electrodes has been used to extend the continuous current rating of a commercial interrupter from 1200 A to 13 kA. Two second generation devices with special electrode materials are currently being developed for use with a special actuator and are intended to extend the continuous rating to 25 kA.