Study on GIS substation for the insulation coordination

Early warning system based on the detection of UHF SF6 partial discharge (PD) signals is a necessary means for the protection of Gas-Insulated Switchgear (GIS) in service as well as the power system to which it is connected. In order to ensure the safe and reliable operation of GIS, it is important to adopt an effective diagnosing method, which is able to identify signals of harmful defects promptly.. Although, a number of insulation coordination studies have discussed controlling over-voltages due to lightning and switching in Gas Insulated Switchgear (GIS) and transformers, not many deal with the additional complexity raised when cables are used to connect overhead lines to the new equipment. An introduction is provided to the sensitivities which affect the magnitude of fast front transients occurring in a typical arrangement including overhead-lines connected to GIS and transformers using short cable sections. This considers factors including lightning, cable length, tower footing impedance and substation running arrangements. Generic sensitivities will be examined for a 400 kV circuit, using studies carried out in EMTP to establish the nature of these over-voltages within the substation and the effectiveness of control methods to mitigate their impact.