Investigation of long-term reliability for solid insulated switchgear

SF₆ gas is applied widely to medium voltage switchgear because of its high insulation reliability and down-sizing ability. However, SF₆ gas was placed on the list of greenhouse gases under the Kyoto Protocol in 1997. Since then, the investigation and development concerning SF₆ free or less has carried out activity. Therefore, we focused on solid materials with higher dielectric strength than SF₆, and we have developed solid insulated switchgear (SIS) achieved by molding all main circuit. A new epoxy casting material is applied, which contains a great deal of spherical silica and a small amount of rubber particles. This new material has the high mechanical strength, high thermal resistance, high toughness, and also high dielectric strength because of directly molding the vacuum bottle, as well as reduced size and high reliability. This paper describes about the long-term reliability of SIS using a new epoxy casting material. We carried out seismic tests, heat cycle tests, heat shock tests and long-term withstand voltage tests for about 5 years. As a result, it was confirmed that SIS had an excellent characteristics in all tests. The effectiveness of the development material and the reliability of SIS were verified.