PURPOSE:To suppress the abnormal voltage low impressed to a cycloconverter in abnormality, by providing thyristers anti-parallelly connected and a protection circuit where a resistor is connected in series thereto between each phase of the secondary winding. CONSTITUTION:Between each phase of the secondary winding of an induction motor 1 are connected thyristers 10A and 10B anti-parallelly connected and a protection circuit 10 to which is connected a resistor 10C in series. When abnormal voltage is set up between the terminals of the secondary winding, a thyrister on the side, where the abnormal voltage in the protection circuit 10 turns out in the forward direction, is ignited by a turn-ON circuit 11 and the resistor 10C is connected between the secondary windings through the thyrister to suppress the voltage, by which can be reduced the breakdown strength against excess voltage of the thyrister bridge in cycloconverter.
展开▼
