Circuit breaker.

摘要

Output current of secondary winding of a current transformer (21) corresponding to current value of an A.C. power line (1) is led to series connection of an electric power circuit (500) and resistors (40,41); voltages obtained across the resistors (40,41) are input to a time delay circuit (70) which ignites a load break contact (200) in the A.C. power line (1) when an accident overcurrent flows in compliance with tripping characteristics. A quasi output signal or reference signal for testing of D.C. voltage is applied to the time delay circuit (70) when any current does not flow in the A.C. power line, thereby to enable tripping test of the circuit breaker as it is connected to the actual power line.