Differential current fault protection for an ac/dc hybrid system and

Abstract

A system of protection for an AC/DC hybrid electric power generation and distribution system having an AC portion comprising at least one source of AC power producing AC current coupled by first power feeders to a DC portion comprising at least one AC to DC converter producing DC current, the DC current being coupled by second power feeders to utilization equipment, comprises AC current sensors producing current sense signals proportional in magnitude to the AC current and DC current sensors producing current sense signals proportional in magnitude to the DC current. The AC current sensors define an entrance to a zone of protection, and the DC current sensors define an exit from the zone of protection. The AC and DC current sense signals are relationally compared to detect the presence of a differential current fault within the zone of protection. The protection system further discriminates the location of the fault between the AC portion and the DC portion of the hybrid power system by monitoring the ripple content in the sensed AC current. The relationship function utilized varies with the type of AC to DC conversion equipment to compensate for the power loss and transformer step up or down ratio (if used) to ensure tracking of the current level between AC current and DC output current. In addition to differential current fault protection, the instant invention detects shorted and open rectifiers, phases, and sensors.