IMPROVEMENT OF DETECTION SYSTEM FOR WIRE BREAKING TROUBLE

PURPOSE:To reduce wrong detection by deciding apparent wire breaking trouble when a load current is not more than a negative specific value even when the variation value of a zero-phase current is a set value. CONSTITUTION:Up-to-data (V01, V1, etc.) on the zero-phase current and load current of each power distribution line of an input port PI are fetched and stored at specific intervals of sampling time (e.g. 0.5sec). Variation values of the zero-phase current and load current of each power distribution line are calculated at every sampling time to select maximum variation values successive ly. When the maximum variation values are larger than a set value (e.g. 40mV) and maintained for longer than a set detection time (e.g. 7sec) and variation in the load current of the power distribution line is smaller (e.g. -50A) than a negative value (e.g. -0.2A) close to 0, a CPU decides that the power distribu tion line is broken, and output a voltage to its output port OP to put a thyristor SCR in operation, thereby displaying the wire breaking trouble.