| 摘要 |
PROBLEM TO BE SOLVED: To prevent the malfunction of a differential relay caused by an excited rush current which is generated in case that another transformer is energized in addition to one transformer. SOLUTION: This differential relay (1-3.9) detects the difference between the primary and secondary currents (ip) and (is) of a transformer 1 and compares the effective value of the current value (id) with a set value ids, and outputs a trip signal when the current difference id is large. In this case, this is provided with a malfunction preventive circuit comprising an integration circuit 4 which gets the magnetic flux ϕ of a transformer by integrating the primary voltage of the transformer, a comparison circuit which compares this magnetic flux ϕ with a set value ϕs and outputs a signal at the time of ϕ>ϕs, and a logical circuit 81 which checks the output of a trip signal in case that there is output of the comparison circuit 7. Since the magnetic flux ϕof the transformer is small at the timer of internal accident and is large at the time of excitation rush, it can prevent the malfunction of the differential relay at the time of excitation rush. |
