Practical design considerations for application of GIS MV switchgear

In a recent biotechnology facility project, the decision was made to require arc-resistant medium-voltage (MV) switchgear for the safety of operating personnel. The available service voltage was 26.4 kV, limiting the availability of proven designs of arc-resistant switchgear. As a result, the owner considered use of medium-voltage gas-insulated switchgear (GIS) with vacuum circuit breakers. Once this decision was made, consideration was given to using the same class of switchgear for the 4.16-kV voltage equipment in the facilities. This offered advantages of uniformity, commonality of spares, and simplification of operator training. This paper focuses on the rationale for selection of GIS switchgear, and the design considerations that had to be addressed as the project moved from concept to installation to operation. Among the issues discussed are the following: space requirements for conventional and GIS equipment; arc-resistant performance of GIS equipment; design commonality between 4.16- and 26.4-kV equipment; installation (cable issues, foundations, workspace, etc.); environmental considerations; total cost of ownership; reliability/availability; operational experience.