Method and apparatus for determining frequency of an alternating current signal of an electric power system
First Claim
1. An apparatus for determining frequency of an alternating current (AC) signal of an electric power system, said AC signal having a period between zero crossings thereof, said apparatus comprising:
- means for measuring the period of said AC signal between one of said zero crossings and a subsequent one of said zero crossings to provide a measured period value; and
a processor comprising;
a memory collecting at least five consecutive values of said measured period values, and a routine choosing a median value from said measured period values and determining said frequency based upon said median value.
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Accused Products
Abstract
A protective relay determines frequency of an AC signal of an electric power system. The protective relay includes a circuit measuring the AC signal period between zero crossings to provide a measured period value. A microprocessor includes a random access memory having a five-element array, which collects five consecutive values of the measured period values. A microprocessor routine chooses a median from the measured period values and generally determines the frequency based upon the median. The median is ignored and the previously determined line cycle period is adjusted to determine the new line cycle period if: an absolute value of a difference between a last value of the measured period values and a previously determined line cycle period is not less than a predetermined value; and the last value of the measured period values is within the limits of the array.
57 Citations
19 Claims
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1. An apparatus for determining frequency of an alternating current (AC) signal of an electric power system, said AC signal having a period between zero crossings thereof, said apparatus comprising:
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means for measuring the period of said AC signal between one of said zero crossings and a subsequent one of said zero crossings to provide a measured period value; and
a processor comprising;
a memory collecting at least five consecutive values of said measured period values, and a routine choosing a median value from said measured period values and determining said frequency based upon said median value. - View Dependent Claims (2, 3, 4, 5)
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6. A method for determining frequency of an alternating current (AC) signal of an electric power system, said AC signal having a period between zero crossings thereof, said method comprising:
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measuring the period of said AC signal between one of said zero crossings and a subsequent one of said zero crossings to provide a measured period value;
collecting at least five consecutive values of said measured period values;
choosing a median value from the consecutive values of said measured period values; and
determining said frequency based upon said median value. - View Dependent Claims (7)
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8. A method for determining frequency of an alternating current (AC) signal of an electric power system, said AC signal having a period between zero crossings thereof, said method comprising:
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measuring the period of said AC signal between one of said zero crossings and a subsequent one of said zero crossings to provide a measured period value;
collecting at least five of said measured period values;
determining at least two highest values of said measured period values;
determining at least two lowest values of said measured period values; and
determining said frequency based upon said measured period values excluding said at least two highest values and said at least two lowest values. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification