CURRENT RELAY WITH TIME CHARACTERISTICS IN INVERSE RATIO TO CURRENT

摘要

The invention relates to a current relay having a time-current characteristic in inverse ratio, meant to survey the homopolar current in medium-voltage systems with insulated neutral wire or resistor earthing. According to the invention, the relay comprises an adapter-transformer (1), a harmonic rejection filter (2) and a rectifier (4), the signal from the rectifier output being applied on one hand to a relay with adjustable current threshold (5) and on the other hand, to a time relay (7) with time characteristic in inverse ratio to current, both relays (5 and 7) controlling by means of an AND gate the operating element (8) which switches off the damaged line where the fault current exceeds a preset level for a period of time longer than the preset limit.