Diagnostic testing of contacts in gas insulated substations

A method for diagnostic testing of electric contacts and joints inside gas insulated substations (GIS) that overcomes the limitations of conventional methods is proposed. The method relies on passing current pulses with peak values up to the rated load current through the GIS section to be examined and measure the resistance accurately. In degraded or overstressed contacts certain nonlinear and/or irreversible phenomena related to the temperature rise in the minute contact spots will occur. Thus, if the resistance is not reproducible or varies with the magnitude of the applied current, this indicates that one or more contacts have a too high resistance. A prototype instrumentation is developed and tested under realistic conditions on 145-420 kV GIS installed in the grid.