| 摘要 |
PURPOSE:To prevent the control/rectify element from being broken in a circuit breaker even if the control/rectify element in a shunt is not fired by sustaining the firing condition of the control/rectify element in the circuit breaker connected nearer to a converter than the shunt if the control/rectify element in the shunt is not fired when a load is grounded or shortcircuited. CONSTITUTION:When a ground or shortcircuit fault occurs in an induction motor 2, the thyristor 5 in a shunt 3 is fired at first. When the voltage of a voltage detector 22 connected across the thyristor 5 drops below a threshold level, the thyristor 13 in a circuit breaker 12 is extinguished. Furthermore, a unit switch 8 is released upon elapse of a predetermined time. On the other hand, if the voltage of the voltage detector 22 is higher than the threshold value, it is considered that the thyristor 5 is not fired and the fired condition of the thyristor 13 is sustained. Upon elapse of a predetermined time under this state, the unit switch 8 is released. By such arrangement, the thyristor 13 can be protected from breakdown. |
