Protective relays and methods
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United States of America Patent
Stats
-
Nov 29, 1988
Grant Date -
N/A
app pub date -
Apr 24, 1987
filing date -
Apr 24, 1987
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
Protective relay for use in an electrical power system having electrical conductors which are energizable with an AC voltage. The protective relay includes a circuit for sensing the AC voltage to produce an AC output that has zero crossings and a time period between zero crossings, a circuit for supplying an electrical signal representing a preselected pickup value of volts-per-Hertz for the relay, and a circuit responsive to the AC output and to the electrical signal for generating an electrical level as a function of both the time period and the pickup value and for producing an output signal for the relay when the AC output exceeds the electrical level. In this way, the output signal is produced when a volts-per-Hertz value of the AC voltage exceeds the preselected pickup value of volts-per-Hertz for the relay. Other protective relay apparatus and methods are also disclosed.
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