Apparatus for detecting arcing and overcurrents in DC electrical systems subject to cyclic disturbances

Arcing in dc electrical systems (1) subject to cyclic disturbances is detected by a current sensor (13), and a bandpass filter (17) sensitive to arcing noise, which filters the sensor current. The absolute value of the bandpass filtered signal (19) is integrated over repetitive intervals in a resettable analog integrator (27). A low cost microprocessor (25) samples and resets the analog integrator (17) at a frequency below the pass band and generates a time attenuated accumulation of the samples that produces an arcing signal if it reaches a predetermined limit. To improve nuisance immunity, the sensed dc current (15) is compared in a high speed comparator (37) to the average sensed dc current (35), and only samples taken by the microprocessor (25) during a predetermined time period after the sensed dc current (15) exceeds the average sensed dc current (35) in a predetermined manner are accumulated. The average sensed dc current (35) is also used by the microprocessor (25) to provide overload protection.