| 摘要 |
PURPOSE:To improve the economy of a thyristor capacity by selecting the output of a ladder signal generator which sets specific design values of a motor current and a rotating speed and comparing the output with the actual rotating speed, thereby controlling a starting thyristor. CONSTITUTION:A starting thyristor 6 is connected to a squirrel cage induction motor 3, and a ladder signal generator 7 which generates a ladder signal according the specific design values of a motor current and a rotating speed corresponding to the starting characteristics of a load 5 is provided. One of a plurality of ladder signals is selected by a selector 9, is compared by a comparator 8 with the signal of a tachometer generator 4, and a signal of firing angle control is instructed to the thyristor 6 when the difference becomes higher than the prescribed value. Accordingly, the rated current value of the thyristor 6 can be selected to a value equal to that of the motor 3 by stepwisely increasing the voltage applied to the motor 3, thereby improving the economy of the thyristor capacity. |
