| 摘要 |
PURPOSE:To detect the disconnection on secondary side by judging whether predetermined relation is present between the phase voltages of three phases on a PT secondary side, line voltage and voltage phase differences between the phases and the line voltage. CONSTITUTION:An input part 4 receives voltage from a three-phase PTC and, when the magnitude of phase voltage is larger than a value epsilon1, detection circuits 5-7 emit outputs and, when line voltage is smaller than a value K, detection circuits 8-13 perform output operation. Phase difference judge circuits 14-16 perform output operation when each phase voltage is delayed by an angle epsilon2 from line voltage and voltage judge circuits 17-19 issue outputs when the line voltage is smaller than a value K2. PT secondary circuit disconnection detection signals S1-S7 are obtained through the operation means of AND circuits 20-22, AND circuits 23-25 wherein one of input terminals is a prohibiting terminal, an AND circuit 26 and an OR circuit 27. By this constitution, the disconnection of a secondary circuit can be detected from the outputs of one set of three-phase output circuits of PT and, even when there is other line load in the secondary circuit, the disconnection of the secondary circuit can be certainly detected. |
