Abstract: In a circuit for the simulated testing of a high voltage direct current switch, which arrangement includes a first direct voltage source producing a high current and low voltage output, a first auxiliary switch and a first inductance both connected in series with the source and arranged to be connected to the switch to be tested, an auxiliary voltage source having a low current and high voltage output and arranged to be connected to the switch for stressing it to its voltage breakdown level, the simulation produced by such circuit is improved by the provision of a second inductance connected to the auxiliary voltage source and arranged to be connected in series between the auxiliary source and the switch to be tested, and a second auxiliary switch connected in series with the auxiliary voltage source and arranged for operatively connecting the auxiliary source across the switch to be tested at a time after the opening of such switch and before the current through the switch, produced by the first voltage sour