| 摘要 |
PURPOSE:To suppress the occurrence of ferro-resonance, by closing a switch by means of a signal from a detection control circuit which detects ferro-resonance thereby to connect a suppressed impedance component to a secondary circuit of a potential transformer only when ferro-resonance occurs. CONSTITUTION:When an electric shock is generated by opening of a breaker, an abnormal current with a peaked waveform flows as the primary current of a potential transformer 1. The peak value is about ten times as high as that in a stationary state. Therefore, the detected voltage also increases to a value larger than a preset value. A switch 7 is closed by a signal from a detection control circuit 8, so that a damping resistor R as a suppressed impedance component 6 is connected to a secondary circuit of the potential transformer 1. By the damping resistor R, the fractional harmonic vibration due to ferro-resonance is suppressed, therefore, no abnormal voltage is generated in the circuit of the potential transformer 1. |
