| 摘要 |
PURPOSE:To make it possible to apply an inspection input directly on a bandpass filter without requiring any adder by providing an inspecting means for inputting an inspection signal through a resistor to the inverter input terminal of an operational amplifier forming an analog filter element which is a component of a fault detecting means. CONSTITUTION:When an inspection input is not present, 0V at the inspection input terminal 31 of a bandpass filter 3 is applied through a resistor 32 onto the inverted input terminal of an operational amplifier 37. Since the inverted input terminal of the operational amplifier 37 is 0V at all times, inspection input is not responsive at all to the bandpass filter 3. In other words, an actual input superposed by transient DC component through response to a normal bandpass filter is passed through the bandpass filter 3 where transient DC component is removed and only commercial frequency component is derived. At the time of inspection input, the bandpass filter 3 corresponds to a lowpass filter and the filter characteristics do not alter in the basic commercial frequency region. This realizes a highly reliable overcurrent relay having simple circuitry. |
