IEC 62271-204:2011 applies to rigid HV gas insulated transmission lines (GIL) in which the insulation is obtained, at least partly, by a non-corrosive insulating gas, other than air at atmospheric pressure, for alternating current of rated voltages above 52 kV, and for service frequencies up to and including 60 Hz. This standard cancels and replaces IEC/TS 61640:1998. It is a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - update to be in line with IEC 62271-1:2007 and 62271-203 and alignment of the voltage ratings and the test voltages; - addition of new information for gas tightness and corrosion protection. This publication is to be read in conjunction with IEC 62271-1:2007.