Eaton Corporation

Lifeng Yang

Robert Tracy Elms

Deborah Kaltwasser Mort

An electric power system relay includes a simulator that substitutes test values of current and voltage for sensed values for use by relay logic to perform specified relay functions, but without loss of the relay protection functions. The sensed values of current at least are monitored even while the test values are being used by the relay logic. If the monitored sensed values exceed a threshold value, a data switch operates to return to use of the sensed current and voltage values by the relay logic. In addition, the sensed values of current and voltage replace the test values, if a time interval longer than that required to perform the specified relay functions using the test values has expired.

Electric power system relay and on-line method of testing same

Apparatus for determining the frequency of an ac power signal, includes sensing circuitry to sense the ac signal. In a digital implementation of the invention, a double average of the samples is generated by a processor as the sum of the most recent sample, twice the next most recent sample plus the third most recent sample. The least mean square of a running window of the most recent double average signals is generated to avoid discontinuities at the zero crossings and to reduce the effects of noise. The frequency is determined from this least mean square value of the window of double average signals. As implemented in a protective relay, a trip signal is generated if the frequency is out of limits.

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Pittsburgh, PA, United States of America

Lifeng Yang