An overcurrent protection apparatus

摘要

An overcurrent protection apparatus is provided comprising a current transformer (4) for detecting current in an AC electric line (1). A first rectifier (5) rectifies the output current of the current transformer (4) and a capacitor (12) is coupled across the positive and negative outputs of the first rectifier (5). Circuit breaker means (2, 10) are provided for disconnecting the AC current line. Switching means (25) are coupled across the output terminals of the first current transformer (4). A second rectifier (24) is provided for rectifying the output of a second current transformer (23) connected to the AC electric line (1). A resistor (26) is coupled across the positive and negative outputs of the second rectifier. A reference voltage generator (13) generates a predetermined reference voltage while a pulse signal generator (16) generates a control signal for varying the duty ratio of operation of the switching means (25) in proportion to the voltage across the capacitor (12) when the voltage exceeds the reference voltage value. The circuit breaker means (2, 10) operate to disconnect the AC electric line (1) when the voltage across the resistor (26) exceeds a predetermined value. <IMAGE>