Protective relay circuit providing a combined distance and overc

Details Protective relay circuit providing a combined distance and overc Protective relay circuit providing a combined distance and overc

1977-01-31

1978-05-30

Moose, Jr., Harry E.

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific quantity comparison means

361 83, 361 87, H02H 328

Patent

active

040926907

ABSTRACT:
The protective relay circuits herein provide a combined distance and overcurrent type of function. The protective relay circuit includes an a-c level detector or bi-polar threshold circuit to which the quantity I (Z.sub.R - Z.sub.F) is applied. The quantity I is the current in the line, Z.sub.R is a replica or reference impedance corresponding to the lines being protected and Z.sub.F is the line impedance to the fault from the relay measuring point. IZ.sub.F is equal to V, the voltage input to the relay. An output is provided from the a-c level detector only when the quantity I (Z.sub.R - Z.sub.F) exceeds a predetermined value. The output of the level detector is compared in a coincidence circuit, or AND gate, with a polarizing signal. The detection of coincidence for a selectable predetermined time period, as measured by a characteristic timer, results in an output signal for use in controlling operation of the trip coil of the circuit breaker. The protective relay circuit may be used on series-capacitor compensated lines as well as on uncompensated lines. When the protective relay circuit is used on a compensated line, the a-c threshold level of the level detector is set to be a function of the breakdown voltage of the spark gap protecting the series compensating capacitor.

REFERENCES:
patent: 3277345 (1966-10-01), Waldron
patent: 3374399 (1968-03-01), Dewey
patent: 3898530 (1975-08-01), Perez-Cavero
patent: 3938007 (1976-02-01), Boniger et al.
patent: 4034269 (1977-07-01), Wilkinson

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