Symmetrical fault current detector

Details Symmetrical fault current detector Symmetrical fault current detector

1991-03-12

1993-01-19

Stephan, Steven L.

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

361 87, H02H 3087

Patent

active

RE0341630

ABSTRACT:
Excess currents due to faults in an electrical power system are generally larger than excess currents due to the magnetization of distribution transformers. Discrimination has hitherto relied on a threshold detector. Magnetizing currents are, however, asymmetrical, whereas fault currents are symmetrical. A detects symmetrical current waveforms on a conductor 1 and thus discriminates between a fault and a magnetizing excess current. A resistor 4, placed across the output terminals of a bridge rectifier 3 has a resistance selected so that the voltage across it exceeds the breakdown voltage of trigger diodes 7 and 8 when the current in conductor 1, in any half cycle, exceeds a desired maximum. Capacitors 13 and 14 will thus only both charge up in response to excessive symmetrical current. A logic control 23 is connected via lines 21 and 22 to detect such a condition.

REFERENCES:
patent: 2316289 (1943-04-01), Sandstrom
patent: 3962606 (1976-06-01), Burns et al.
patent: 4454557 (1984-06-01), Hurley
patent: 4544980 (1985-10-01), Serrie et al.
patent: 4553188 (1985-11-01), Aubrey
patent: 4583004 (1986-04-01), Yearsin

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