IMPROVEMENT IN DISCONNECTION DETECTING SYSTEM

PURPOSE:To elevate the sensitivity and accuracy of detecting disconnection by adding a simple phase angle measuring circuit or the like to use an absolute value, namely, actual variation value or an approximation thereof for a vector difference of output voltages depending on the zero-phase current immediately before and after a disconnection trouble. CONSTITUTION:An input port PI which transmits a digital output voltage and a phase digital value of a zero phase current transformer D.ZCT for detection of disconnection in distribution lines to respective memories M is provided with terminals 11-14 for the distribution lines. Numeral 5 indicates a filter, 6 an amplification circuit, 7 an A/D conversion circuit, and 8 is a phase measuring circuit. The maximum of an absolute value or the approximation thereof for an output voltage vector difference of the zero phase current transformer D.ZCT for detection of disconnection in the distribution lines is selected by control with a CPU every sampling time and if the maximum is larger than the feeder detection sensitivity and continues for a set time, it is determined that there is a disconnection trouble in the distribution line that indicates the largest of the voltage variation. This provides a higher accuracy and sensitivity of detecting disconnection as compared with the conventional system only using the absolute value for arithmetic difference of the output voltage.