PURPOSE: To make charging polarity variable in addition to use as a single power supply by applying the second output voltage on the capacitor of a voltage source circuit through the charging breaker of the voltage source circuit, and cutting off an advanced current flowing through the voltage source capacitor.

CONSTITUTION: Before the short-circuit test, an inputs switch 2 and an auxiliary breaker 5 are opened, and a breaker under test 6 and a breaker 12 for charging a voltage source circuit are closed. When the switch 2 is closed at an arbitrary time, a voltage is applied from a short-circuit generator 1 on the primary winding of a step-up transformer 4 through the switch 2 and a reactor 3 for adjusting the shortcircuit current. At the secondary side of the transformer 4, a closed circuit including the breaker 12 and a capacitor 11 of the voltage source circuit is formed through a high-voltage tap. At this time, the phase-advanced current, which is approximately determined by the generated voltage in the secondary side of the transformer 4 and the capacitor 11, flows through the breaker 12.