145kV GIS Switchgear.

Cable connection is commonly used for indoor connection to GIS, but could also be used outdoors if the transmission line comes underground. The gas-to-air bushing is commonly used outdoors for overhead transmission connections. It is not usually used indoors because of the clearances required around the live, exposed end of the bushing (especialy at HV such as 145kV - you just don't use that voltage in open air indoors). Indoor GIS can be connected to an outdoor, aerial transmission line by use of a bulkhead section that passes through the building wall to an outdoor gas-to-air bushing connection.