Insulation technology in dry air and vacuum for a 72‐kV low‐pressure dry‐air insulated switchgear

A new 72‐kV rated low‐pressure dry‐air insulated switchgear applying electromagnetic actuation and a function that supports CBM has been developed. First, the dielectric characteristics in dry air under lightning impulse application were investigated for bare and insulator‐covered electrodes. The dependence of the breakdown electric field strength on the effective area was found in order to apply it to the configuration design of the insulation mold for the vacuum interrupter. In addition, the dependence of the moisture volume on the surface resistance was found in order to decide the moisture volume in the gas pressure tank. Next, a new vacuum circuit breaker (VCB) was designed. To keep the dimensions the same as in the previous 72‐kV SF₆ gas insulated switchgear, the distance between contacts in the vacuum interrupter must be shorter than in the previous switchgear. The voltage withstand capability between electrodes practically designed for the vacuum interrupter was investigated under DC voltage application, in a small capacitive current breaking simulation. The gap configuration, including contacts and slits, was optimized and the distance was shortened by 11% from the previous switchgear. As a result, the new low‐pressure dry‐air insulated switchgear was designed to be comparable in external size to the previous SF₆ gas insulated switchgear. Using dry air as an insulation medium with low pressure makes it possible to reduce the environmental burden. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(1): 18–24, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21058