Apparatus providing on-line indication of frequency of an AC electric power system
First Claim
1. Apparatus for on-line determination of the frequency of an ac signal in an ac electrical system comprising:
- sensing means coupled to the ac system generating a sensed signal representative of said ac signal;
means generating a double average signal from said sensed signal; and
means generating a frequency signal indicating the frequency of said ac signal from said double average signal.
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Accused Products
Abstract
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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Citations
15 Claims
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1. Apparatus for on-line determination of the frequency of an ac signal in an ac electrical system comprising:
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sensing means coupled to the ac system generating a sensed signal representative of said ac signal;
means generating a double average signal from said sensed signal; and
means generating a frequency signal indicating the frequency of said ac signal from said double average signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. Apparatus providing protection to an ac electrical system comprising:
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sensing means coupled to said ac electrical system and generating digital samples of a selected waveform in said ac electrical system;
digital processing means comprising;
means generating digital double average signal;
means generating a digital frequency signal from said digital double average signal; and
means comparing said digital frequency signal to selected limits; and
output means generating an output when said digital frequency signal is not within said selected limits. - View Dependent Claims (11, 12, 13, 14, 15)
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Specification