| 摘要 |
PROBLEM TO BE SOLVED: To enable a voltage control of high quality with no need for recovery after a frequency-abnormal failure, by continuing operation without disconnecting a static voltage adjusting device from a commercial power system when the frequency of the power system is abnormal. SOLUTION: Frequency abnormality of the commercial power system is detected by a zero-cross detecting circuit 15, a zero-cross interval timing circuit 11 and a frequency comparison circuit 12; and voltage abnormality of the commercial power system is detected by an instantaneous voltage measuring circuit 16, an effective-value calculation circuit 17 and a minimum-maximum-unbalance- ratio comparison circuit 18. A phase control circuit 14 generates gate arc-ignition pulses of a thyristor 4, whose arc-ignition angle at three phase is approximately 30 degrees while the frequency abnormality is detected in the comparison circuit 12, and a trip coil 21 actuates responding to the abnormality detection of the comparison circuit 18. Herein, a frequency-abnormality priority circuit 20 cancels an abnormality-detection output of the comparison 18, when the frequency abnormality is detected in the comparison circuit 12.
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