| 摘要 |
PURPOSE:To alleviate the operating frequency of a field breaker by breaking a thyristor which supplies power to a field coil and then operating the field breaker when no current flows in a discharging circuit even after the prescribed period of time is elapsed thereafter. CONSTITUTION:A field 11 is excited through a thyristor 2 and a field breaker 6 by an AC power source 1, and a discharging resistor 10, a thyristor 9 and a detecting resistor 13 are connected across the field 11. When a breakage signal S1 is presented, the thyristor 2 is broken by a gate unit 3, and the thyristor 9 is simultaneously conducted ON by a gate unit 13, thereby forming a discharge circuit of the field 11. Further, the discharging current is detected by the resistor 13, and when no current is flowed, the field breaker 6 is opened via a controller 5. Accordingly, the field breaker 6 is broken only when the discharging circuit is not formed, thereby reducing the frequency and improving the reliability. |
