Phenomena of leaking electromagnetic waves and high frequency surges from isolated joint of gas insulated switchgear

High frequency surges leaking through the insulated joint of a GIS were measured, using a model GIS, and the phenomena, characteristics and mechanism were clarified based on the experiment and the circuit theory. High frequency surges decrease the impedance of the insulated joint, producing an almost short circuit state, and the coefficient for refraction from the inside of the GIS tank to the grounding system becomes significantly small. In a multi-phase GIS, surges leaking through the insulated joint form the tank-to-tank mode voltage for the different phase tank, generating the voltage equal to the potential of the voltage application tank to ground. On the other hand, no potential to ground is directly generated to the adjoining bus. The amplitude and the frequency of surges leaking through the insulated joint of a GIS bus are almost identical to those calculated from the distributed constant circuit theory. The phenomena can be, therefore, reproduced using the EMTP through the simulation of the line part by the multi-phase distributed constant and the simulation of the insulated joint by the capacitance.