Investigation and development of high voltage vacuum interrupters

Electrical and mechanical subjects are investigated to design and manufacture high voltage vacuum interrupters (HV VIs). In electrical aspects, vacuum breakdowns are experimented to rod-plane and plane-plane models with stainless steel (SUS) and gaps. To overcome the defects of HV VIs in tank-type vacuum circuit breakers, outer shields are proposed. Mechanically, since HV VIs are large and have a heavy moving part and high velocity to cause large impact load and bend conduction rods, elongation and tensile strength tests are given to two metals, one of which is OFHC (oxygen free high conductivity) copper and the other is SUS. One of SUS is heated to a brazing temperature (over 800degC) to compare with the unheated one. With these test results, the buckling strength of OFHC copper and SUS is calculated to decide which to use and the diameter of a rod in a VI. HV VIs are usually used in a high pressure gas, and structure analyses are needed. 72.5 kV 40 kA VIs were manufactured. Lightning impulse test and breaking tests were finished successfully with single phase vacuum circuit breaker.