Patent ID: 7242110
Filing Date: 2007-07-10
Classification: H01H,H02H,H02J,Y02E

Abstract:
1. A control system for canceling load unbalance of a three-phase circuit, comprising: phase current detectors for detecting phase currents caused to flow through a secondary circuit of a current transformer provided in high voltage distribution lines, respectively; a zero-phase current detector for detecting a zero-phase current caused to flow through a residual circuit of the current transformer; phase change-over switches through which phases of the high voltage distribution lines, and primary sides of distribution transformers provided across high and low voltage distribution lines are connected to each other; a control center for, when a magnitude of the zero-phase current detected by the zero-phase current detector is larger than a predetermined value, on the basis of the phase currents of the phases detected by the phase current detectors, respectively, outputting a control signal so that the load of the phase having a maximum current appearing therein is changed over to the phase having a minimum current recognized therein; and a phase change-over slave station for controlling the phase change-over for the phase change-over switches in accordance with the control signal, wherein the control center obtains a limit time for the phase change-over control corresponding to the zero-phase current detected by the zero-phase current detector, and outputs an alarm signal exhibiting that if the time limit elapses, then an over-current grounding relay connected to the residual circuit of the current transformer undergoes malfunction.