Apparatus for detecting and responding to series arcs in AC electrical systems

摘要

Series arcs in an ac circuit (103) are discriminated from other phenomenon by analyzing the timing between pulses (17, 19) in a second derivative (13) of the current signal. A first timer (159) starts timing upon detection of a first pulse (197) in the second derivative of current signal. Time out of the first timer (159) starts a second timer (161) which times a second interval or window during which a series arcing fault will generate a second pulse (19) of opposite polarity to the first pulse. Detection of the first pulse (17) followed by a second pulse (19) of opposite polarity during the window sets a flip-flop (163) to record the event. When a predetermined number of events are counted by a counter (181) within a given time-period set by a third timer (179), an output signal (184) indicating an arcing fault is generated. If the second pulse (19) is generated before the window opens, or a third pulse (43) occurs during the window, the flip-flop (163) cannot be set so that other events such as the switching of a dimmer do not generate a false output signal. <IMAGE>