PURPOSE: To obtain a phase leading current interruption tester in which the lead current interruption can be detected and tested under such conditions a containing desired harmonics by generating a harmonic current immediately before opening a switch to be tested and generating a transient recovery voltage immediately after interruption.

CONSTITUTION: A 50Hz or 60Hz sine wave voltage is applied from a power supply 1 upon starting a test and a basic wave current i1 flows through a series circuit including a switch 2 to be tested. Discharge 7 takes place immediately before opening the switch 2 and a harmonic current i2 flows through a closed loop of a harmonic circuit power supply capacitor 9, a harmonic current reactor 8, a cap 7, the switch 2, and an auxiliary switch 11. The current i2 is superposed on the current i1 to produce a distorted current flowing through the switch 2. The switch 2 is thereby interrupted and the voltage (e) of the power supply 1 is applied to one end thereof while the DC residual voltage of a capacitor 4 for phase leading load is applied to the other end. Furthermore, a current based on the residual charges of the capacitor 9 flows through a closed loop of capacitors 10, 6-a reactor 8 and a DC voltage containing the transient oscillation component of such frequency as prevailing at the time of voltage division 10, 6 is additionally applied to the switch 2. A transient recovery voltage is generated during the voltage division process.