Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Patent
1988-07-13
1989-10-24
Pellinen, A. D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
361 20, 361 77, H02H 326
Patent
active
048766240
ABSTRACT:
A predetermined unsymmetry of a bipolar waveform is detected by apparatus which includes a circuit which generates a pulse for each zero crossing of the waveform. Each zero crossing pulse triggers a first retriggerable one-shot for a first interval T.sub.1. Timing out of the first one-shot triggers a second retriggerable one-shot for a second interval T.sub.2. If both the first and second one-shots have timed out a third one-shot is triggered for a third interval T.sub.3. The intervals are selected such that twice T.sub.1 plus T.sub.2 is equal to the period of one cycle of the bipolar waverform so that triggering of the third one-shot is an indication of a predetermined unsymmetry determined by relative values of T.sub.1 and T.sub.2 of the bipolar waveform. T.sub.3 is selected such that two symmetrical cycles of the bipolar waveform are required to clear the unsymmetry indication. The apparatus is applied to blocking a false trip signal from a reverse current relay in response to the in-rush current when a transformer is energized with little or no load.
REFERENCES:
patent: 4470091 (1984-09-01), Sun et al.
patent: 4589048 (1986-05-01), Takata
patent: 4635157 (1987-01-01), Ebisaka
patent: 4698718 (1987-10-01), Chow et al.
patent: 4763014 (1988-08-01), Model et al.
Gaffin Jeffrey A.
Pellinen A. D.
Studebaker B. R.
Westinghouse Electric Corp.
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