Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Patent
1993-07-29
1995-12-19
Hoff, Marc S.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
361 78, 361 87, H02H 308
Patent
active
054774080
ABSTRACT:
The system includes a blocking counter which is set to 255 quarter cycles and the output contacts of the protective relay are blocked for five quarter cycles if the first order difference between two successive quarter-cycle samples of current is above a selected threshold, referred to as the last previous and the first samples. The first order difference between the first and the next successive (second) samples is compared against a second threshold and the instantaneous value of the current sample is compared against the second threshold. If both comparisons are above the second threshold, then the output contacts are unblocked. If not, such that a constant DC A/D converter output or an A/D spike is indicated, then the outputs remain blocked for the full five quarter cycles, which is sufficient time to permit the A/D spike to disappear and to recognize a constant DC output from the A/D converter.
REFERENCES:
patent: 4446498 (1984-05-01), Stich
patent: 4825326 (1989-04-01), Andow et al.
Schweitzer, III Edmund O.
Tibbals Timothy P.
Hoff Marc S.
Jackson S.
Schweitzer Engineering Labs, Inc.
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