This paper shows the following new aspects of reliability concepts in Gas Insulated Switchgear (GIS) and Gas Insulated Modules (GIM) that are used worldwide as hidden substations, located underground or in a building. The constructional reliability considerations of this paper emphasis the problems of:• SF 6 leakage in connection to the US Environment Protection Agency (EPA) and the solution brought to special shape gaskets through the years.• Spring operating mechanisms and improvement reliability aspects.• Monitoring and diagnostic tendencies of GIS substations in order to reduce maintenance.

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Abstrad-This paper presents underground and hidden Gas Insulated Switchgear (GIs), used in various substation arrangements. It describes the reasons and application of modular, very compact and quick to install of modern GIS solutions.