Transients in hybrid switchgear involving SF and vacuum interrupters

Hybrid switchgear have become popular for medium voltage applications. They usually involve Vacuum Interrupters (VI) immersed in SF6 gas. The presence of SF6 as an insulating medium greatly reduces the clearance requirements, thus enabling the development of compact switchgear convenient to be installed in locations with space constraints. The insulating gas, however, modifies the dielectric characteristics of the switchgear. Hence comprehensive investigation is required to assess the behavior of the switchgear during switching transients. This paper attempts to study the transient recovery voltages associated with hybrid switchgear and compare those with that of air insulated switchgear through simulation in PSCAD/EMTDC as well as through observations during switching tests.