APPARATUS FOR ENVELOPE DETECTION OF LOW CURRENT ARCS

摘要

Arcing faults in an ac current are detected by apparatus which is responsive to a predetermined randomness in step increases in the current to eli minate false tripping caused by regularly occurring discontinuities produced by loads s uch as dimmers. A signal conditioner generates a bandwidth limited di/dt signal having pulses produced by the step increases in current. In one embodiment, a first tracking c ircuit tracks the envelope of the di/dt signal with a first time constant. A second tra cking circuit also tracks the di/dt envelope, but with a second, shorter time constant . An arcing fault is indicated if the second tracking signal falls to a predetermined fraction of the fist tracking signal. This circuit may be used alone to detect arcing fau lts or to increase the sensitivity to arcing faults over dimmers of a circuit which respon ds to a time attenuated integrated valve of the pulses in the di/dt signal. In another embodiment, the di/dt envelope signal is subtracted from the magnitude of the pu lses before they are applied to the time attenuated integrator, but with the subtract ion time delayed to preclude attenuation of the first pulse.