Pressure relief tests on varistors for the series compensation banks installed at the Montagnais substation

For the series compensation banks currently being installed an the Hydro-Quebec network, it was decided to verify the performance of the pressure relief devices on the varistor units with the capacitor discharge superimposed on the fault current. This paper gives the calculations done to evaluate the expected stresses on a failed varistor unit. It is followed by a description of the tests required and the tests circuits developed to reproduce the capacitor discharge current added to the fault current. The last sections give a description of the test units and presents the results obtained. This paper is concluded by a discussion of the results and of the useful data obtained from the tests