Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific quantity comparison means
Patent
1977-01-06
1978-08-08
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific quantity comparison means
361 83, H02H 338
Patent
active
041060717
ABSTRACT:
Apparatus for protecting a power system or a portion thereof against the effects of subsynchronous current oscillations is disclosed. A signal representative of or proportional to the subsynchronous current is developed via synchronous modulation and bandpass filter techniques. This signal is fully rectified to produce a waveform from which information can be garnered from both the positive and negative half-cycles.
A peak holding and peak status circuit then compares successive peaks of the rectified signal, which circuit is adapted to recognize only those peaks having increasing amplitude. The output of the peak holding and peak status circuit is utilized by three comparator circuits which individually employ differing reference voltage levels for overall evaluation purposes.
Given a predetermined frequency range of interest for the subsynchronous current, three timing circuits are used to insure that recognizable peaks of the rectified signal fall into the range of interest and exist for a predetermined evaluation time period. The evaluation time period is automatically changed by one of the comparator circuits if the instantaneous subsynchronous current exceeds its predetermined threshold level. A trip and count signal is then generated by the detection apparatus, regardless of the time period used for evaluation.
REFERENCES:
patent: 3558986 (1971-01-01), Schleif et al.
Church Larry L.
Sun Shan C.
Lackey D. R.
Moose Jr. Harry E.
Westinghouse Electric Corp.
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