Pressure rise due to a high current internal arc in an MV cubicle model

The author discusses pressure-rise tests in SF₆ and air on a full-scale model of a 12 and 24 kV three phase MV switchgear with currents from 5 to 20 kA RMS at 10 kV RMS copper electrodes (diameter 30 mm) and an iron plate as a counter electrode and an operating pressure of 0.12 and 0.14 MPa. The tests showed that, even with reduced filling pressure for air, no acceptable correspondence between the test results can be achieved. The rapid increase of pressure that was measured inside the tank, resulting from a short-circuit current, showed that the use of an overpressure relief device almost always leads to an expulsion of hot and decomposed SF₆ gas, which is due to the low ratio between working pressure and the setting of the safety pressure relief device