| 摘要 |
PURPOSE:To block the flow of a current to an element wherein commutation fails from a load at the time of commutation faliure by using commutation elements which can be controlled as feedback commutation elements. CONSTITUTION:When commutation fauls, the current detected by a current transformer 6 increases quickly, and the output of a comparator 8 is stopped. Then, the output x of a logic circuit 9 is stopped, and all feedback thyristors T71-T76, which are to be turned ON after this time point, are gate blocked. In the meantime, the tyristors T71-T76 which have been already turned ON at the time point of the occurrence of the commutation failure continue to be ON even though they are gate blocked. But, by and by, they are naturally turned OFF by AC electromitive force. The same operation is performed in thyristors T21-T26. Therefore, thyristros T22, T23, and T25 are not turned ON after this time point. The thyristors T21, T24, and T26 which have been already turned ON at this time point are extinguished by auxiliary inpulses and the like. |
