| 摘要 |
PURPOSE:To improve safety and reliability, by a method wherein the actual period of AC voltage is detected by a voltage period detecting means and control operation is stopped when the abnormality of power source frequency is detected. CONSTITUTION:A phase control circuit 9 for a thyristor rectifier 4 is constituted of an amplifier 9a, comparing respective signals from a current detector 7 and a current commander 10, a synchronizing signal generating unit 9b, an integrator 9c, a comparator 9d and a gate ignition circuit 9e while the pulse from said igniting circuit 9e are distributed to respective thyristor gates. In this case, a transmitting circuit 12, capable of setting the range of predetermined set period, and a periodical signal generating period measuring circuit 13 are provided while the measuring circuit 13 is constituted of a voltage period detecting means 13a, a comparing means 13b and a phase control operation stopping means 13c. When an actual period is decided that it is in the range of the set period, a gate signal output stopping signal 14 is outputted to the gate igniting circuit 9e.
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