| 摘要 |
PURPOSE:To prevent unnecessary operation of circuit breakers by switching the operational sensitivity of a current differential relay to a low level for a predetermined period of time on the condition of occurrence of closing command for the circuit breaker at its end. CONSTITUTION:A current differential relay 3A takes in the voltage at terminal A from a line 5A, then an input processing section 6A samples the voltage simultaneously with current taken through a current transformer 2A thereafter the voltage and the current are subjected to A/D conversion. Operating section 7A in the current differential relay 3A performs sensitivity switching operation of the current differential relay 3A based on a circuit breaker closing command. The sensitivity switching operation is carried out by means of AND gates 18, 22 and a NOT gate 21 so that a high sensitivity current differential relay 15A is switched to a low sensitivity current differential relay 16A thus tripping the circuit breaker through AND operation with a current compensation undervoltage relay 13A. By such arrangement, unnecessary function of circuit breaker can be prevented reliable until the current compensation undervoltage relay 13A is reset. |
