In-situ insulation test of 400kV GIS

To guarantee the Insulation strength of gas insulated substations (GIS), a number of different voltage waveforms, e.g. switching, lightning and AC, have to be applied to the GIS after installation. Because of very huge dimensions of GIS for nominal high voltages, it is not possible to carry out these tests in the factory and parts of the whole system have to be delivered and put together to build the complete GIS. As the result, all insulation tests have to be performed in-situ. Even if different systems are tested in the factory, because of problems occurring during the transportation and mistakes by the installation, the insulation strength of the whole GIS can be degraded. In this paper, the test set up and the measurement results of a 400 kV GIS installed for the Mobarakeh steel industries, Isfahan, IRAN, are reported. Because of relatively large capacitances of the gas Insulated Substations, the power ratings of the test voltage sources have to be very high. For this purpose, different possible solutions and the measurement results are discussed in detail.