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

Abstract

SUMMARYA 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 SF 6 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 SF 6 gas insulated switchgear. Using dry air as an insulation medium with low pressure makes it possible to reduce the environmental burden.

Study on the characteristic decomposition components of air-insulated switchgear cabinet under partial discharge

“…3,4 Air-insulated switchgear cabinet is a closed equipment integrated by circuit breaker, isolating switch load switch, mutual inductor and other protection device. 5 Due to the closed structure, the insulation defect-induced damage can be more serious than that in the open-type equipment once the discharge occurs.…”

Study on oxygen/nitrogen gas mixtures for the surface insulation performance in gas insulated switchgear

“…On the other hand, this gaseous insulation medium was classified as a greenhouse gas at the Kyoto protocol climate conference in 1997, which has limited its use. In order to find a SF 6 substitute, researchers have examined SF 6 mixture gases [1][2][3], N 2 , N 2 /O 2 mixture gas, dry air [4,5], and CO 2 gas [6,7] for alternative insulation gases. Alternative gases, however, have a problem in insulation performance compared to SF 6 .…”

“…Studies [17][18][19][20][21] presented the surface discharge characteristics and their mechanisms in compressed gases, vacuum and air. On the other hand, it was relatively insufficient to examine the evaluation of the surface insulation performance and the surface discharge characteristics in eco gases such as N 2 , N 2 /O 2 mixture gas, and dry air [4,5,22]. Recently, Sato et al [23] developed a solid insulated switchgear (SIS) in which an epoxy casting material was used for solid insulation.…”

“…Recently, Sato et al [23] developed a solid insulated switchgear (SIS) in which an epoxy casting material was used for solid insulation. Furthermore, researchers [5,11,24,25] have examined gas insulated switchgears (GIS) in which solid insulation and dry air were used. The gaseous insulation media and insulation methods of these ecofriendly composite insulation devices were eco gases (i.e., vacuum and air) and composite insulation with solid insulation respectively.…”

“…Thus, it is required to study the performance and reliability of surface insulation in the eco gases for SIS and GIS. Precedent researchers have studied on the selection of eco gases with respect to low global warming potential [4,10,11] and insulation properties on an electrode [4,5,[24][25][26][27]. These studies have only focused on the insulation characteristics of the eco gases and on the insulation method using the coated electrode in order to compensate their dielectric strength which was lower than the dielectric strength of SF 6 .…”