| 摘要 |
PROBLEM TO BE SOLVED: To prevent a mis-output of a device failure caused by an overload when an overload operation was carried out when the demand for electric power reached a peak. SOLUTION: The main detecting relay unit of a digital relay is provided with a monitoring circuit A consisting of a discriminating formula calculating part 13, which discriminates if a formula current IR, R, T <= the setting value Kset of a failure detecting relay 21 × a constant α (α=0.9 for instance), is satisfied, an AND circuit 15, which outputs the AND operation of the output of the contact FXa2 of a relay FX actuated by the output of the failure detecting relay 21 and the calculating part 13, and an on-delaying timer T, which outputs signals if this AND output continues for a certain period of time (60 seconds for instance) or longer. This timer output energizes a normally monitoring and abnormality outputting relay RF. Because no output is made from the AND circuit when IR, S, T>Kset ×α, even if the failure detecting relay 21 is operated, there is no possibility that a device failure is mis-output from the relay RF. In the case of a device failure in which the failure detecting relay 21 continues to operate, however, an accurate warning is outputted. |
