PROTECTION METHOD OF DC CAPACITOR

PURPOSE: To prevent secondary disaster of a DC capacitor in advance by a method wherein, when one internal element out of DC capacitors to be protected is made dielectric breakdown by flowing a constant AC current into the one or two or more DC capacitor(s) to be protected, a change of an AC current is detected to break a charging power source. CONSTITUTION: Both ends of a rectifying circuit D for charging a DC capacitor CX to be protected and a charging protection resistor R are in parallel connected with an AC current flowing capacitor CD, and a DC voltage is charged in the capacitor CX through the rectifying circuit D from an AC power source E, and also a constant fine AC current flows in the capacitor CX by the capacitor CD. Under such condition, when one internal element in the capacitor CX is made dielectric breakdown, electrostatic capacitance of the capacitor CX changes and an AC current flowing in the capacitor CD increases. The change of this AC current is detected by a current converter CT and a breaker B is driven by a controller C, by which the DC capacitor is broken from the AC power source E to be protected.