Coating and barrier within medium voltage GIS (Gas insulated switchgear)

The main purpose of this paper is to investigate cases with atmospheric air and hybrid insulation, where solid insulation is used in addition to air. For solid insulation, convenient polymeric materials are used. With hybrid insulation it is typically two options: Coating or barriers. The properties of convenient polymeric materials are in somewhat extent unknown and less examined for this type of application. Therefore an investigation of the dielectrical behaviour of materials used in medium voltage switchgear on a section with parallel conductors has been carried out. For the execution, experiments were done with power frequency test and lightning impulse voltage. The experiments with coating were done with Raychem heat-shrink tubes. Two types of plastic material where used as barrier. Observations from experiments showed that hybrid insulation with coating gives an increase in breakdown strength compared to air only. Coating should be preferred based on the increase in dielectric strength of the system. However, if the barrier can be used as a mechanical support for the conductors, the barrier could be preferred as the solid insulation.