| 摘要 |
PURPOSE:To pervent an erroneous trip of a carrier protecting relay unit by resetting a proportional gain limiting timer for producing its output at zero phase current flowing time according to the output of a discriminator even if the accident mode varies during the accident to abruptly alter the current. CONSTITUTION:Sampling pulses 22A, 22B are produced at 90 deg. and 270 deg. of zero phase voltage Vo 21 to sample zero phase current Io 23. Accordingly, a sampling- hold circuit 24 produces a negative voltage output, which increases in negative direction after the current abruptly alters. On the other hand, a sampling-hold circuit 25 produces a positive voltage output, which increases in positive direction after the current abruptly alters. The output voltages of the circuits 24, 25 are summed in an arithmetic circuit 26. When the circuit 26 produces the output voltage higher than predetermined value, a discriminator 27 detects it to produce its output signal, which resets a proportional gain limiting timer. Thus, it prevents the erroneous trip. |
