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.
2 Assignments
0 Petitions
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.
89 Citations
28 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)
employing said median value to determine a new line cycle period if: (i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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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)
employing an odd count of said measured period values. -
10. The method of claim 9 further comprising
employing five as said odd count of said measured period values; -
determining a median value of said measured period values; and
determining said frequency based upon said median value.
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11. The method of claim 9 further comprising
employing at least seven as said odd count of said measured period values; -
determining a median value of said measured period values; and
determining said frequency based upon said median value.
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12. The method of claim 9 further comprising
employing at least seven as said odd count of said measured period values; -
determining three values closest to a median of said measured period values;
determining an average value of said three values; and
determining said frequency based upon said average value.
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13. The method of claim 9 further comprising
determining an average value of said measured period values excluding said at least two highest values and said at least two lowest values; - and
determining said frequency based upon said average value.
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14. The method of claim 9 further comprising
determining a median value of said measured period values; -
employing said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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15. The method of claim 9 further comprising
determining a median value of said measured period values; -
employing said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a function of said previously determined line cycle period;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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16. The method of claim 8 further comprising
employing an even count of said measured period values. -
17. The method of claim 16 further comprising
employing at least six as said even count of said measured period values; -
determining two values closest to a median of said measured period values;
determining an average value of said two values; and
determining said frequency based upon said average value.
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18. The method of claim 16 further comprising
determining an average value of said measured period values excluding said at least two highest values and said at least two lowest values; - and
determining said frequency based upon said average value.
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19. The method of claim 16 further comprising
determining an average value of said measured period values excluding said at least two highest values and said at least two lowest values; - and
employing said average value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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20. 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;
a processor comprising;
a memory collecting at least five consecutive values of said measured period values, a routine choosing a median value from said measured period values and determining said frequency based upon said median value; and
wherein the routine of said processor further employs said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; and
, otherwise, adjusts said previously determined line cycle period to determine said new line cycle period.
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21. 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;
determining said frequency based upon said median value;
employing said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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22. 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;
determining said frequency based upon said measured period values excluding said at least two highest values and said at least two lowest values;
employing an odd count of said measured period values;
determining a median value of said measured period values;
employing said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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23. 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;
determining said frequency based upon said measured period values excluding said at least two highest values and said at least two lowest values;
employing an even count of said measured period values;
determining an average value of said measured period values excluding said at least two highest values and said at least two lowest values;
employing said average value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to all of said measured period values; andotherwise, adjusting said previously determined line cycle period to determine said new line cycle period.
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24. 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;
a processor comprising;
a memory collecting at least five consecutive values of said measured period values;
a routine choosing a median value from said measured period values and determining said frequency based upon said median value;
wherein the routine of said processor further employs said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to said predetermined value and is not within array limits;
wherein said array limits are determined by the maximum and minimum values of N consecutive median values where N is an integer; and
otherwise, adjusts said previously determined line cycle period to determine said new line cycle period.
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25. 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;
a processor comprising;
a memory collecting at least five consecutive values of said measured period values;
a routine choosing a median value from said measured period values and determining said frequency based upon said median value;
wherein the routine of said processor further employs said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to said predetermined value and is not within array limits; and
wherein said array limits are determined by the maximum and minimum values of N consecutive median values where N is an integer.
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26. 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;
a processor comprising;
a memory collecting N consecutive values of said measured period values where N is greater than one and odd;
a routine choosing a median value from said measured period values and determining said frequency based upon said median value;
wherein the routine of said processor further employs said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to said predetermined value and is not within array limits;
wherein said array limits are determined by the maximum and minimum values of N consecutive median values, where N is an integer; and
otherwise, adjusts said previously determined line cycle period to determine said new line cycle period.
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27. 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;
a processor comprising;
a memory collecting N consecutive values of said measured period values where N is greater than one and odd;
a routine choosing a median value from said measured period values and determining said frequency based upon said median value;
wherein the routine of said processor further employs said median value to determine a new line cycle period if;
(i) an absolute value of a difference between a last value of said measured period values and a previously determined line cycle period is less than a predetermined value;
or (ii) said last value of said measured period values is greater than or equal to or less than or equal to said predetermined value and is not within array limits; and
wherein said array limits are determined by the maximum and minimum values of N consecutive median values, where N is an integer.
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28. 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;
a processor comprising;
a memory collecting N consecutive values of said measured period values where N is greater than one and odd, 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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Specification