To make a size small, reduce consumption of a contact, and make maintenance of an auxiliary switch unnecessary by connecting a series connecting circuit of a diode and a resistor to a main switch in parallel, and setting a resistance value of the resistor so that current in the diode does not exceed an allowable value when the main switch is opened.
Since a resistor 2 is connected in series to a diode 6, current flowing in the diode 6 can be made low. Therefore, the capacity of the diode 6 is made small. Since current flowing in the resistor 2 is shut off with the diode 6, no arc is generated. Since a resistance value of the resistor 2 is set so that current flowing when accident occurs does not exceed an allowable value of the diode 6, break of the diode 6 is prevented, and reliability of a switch device is enhanced. By setting the product of the resistance value of the resistor 2 and a breaking current wave height value so as to be higher than arc voltage of a main switch 1, commutation of the whole current flowing in the main switch 1 to a circuit of the diode 6 is prevented.
HAYASHI TATSUYA
YAMAMOTO KYOICHI
