Metering and protection system for an A.C. power system

• US 4,300,182 A
• Filed: 08/09/1979
• Issued: 11/10/1981
• Est. Priority Date: 08/09/1979
• Status: Expired due to Term

• Current Assignee: Edmund O. Schweitzer III
• Original Assignee: Edmund O. Schweitzer III
• Inventors: Schweitzer, Edmund O. III
• Primary Examiner(s): Miller, J. D.
• Assistant Examiner(s): EISENZOPF, REINHARD
• Application Number:
  US06/065,158
• Time in Patent Office: 824 Days
• Field of Search: 361/79, 361/65, 361/80, 361/82, 361/85, 361/93, 364/727, 364/728, 364/483, 324/77 G, 324/83 Q, 324/141
• US Class Current: 361/79
• CPC Class Codes: G01R 21/00 Arrangements for measuring electric power or power factor G01R7/12 takes precedence
• CPC Class Codes: H02H 3/38 responsive to both voltage and current; responsive to phase angle between voltage and current

Abstract

A system for electronically metering an A.C. electrical power system to derive performance parameters such as real and reactive power useful in revenue metering and fault protection applications. Voltage and current sensors associated with the power system provide isolated output signals proportional to the voltage and current in the system. From these signals finite-duration impulse-response filters periodically determine Walsh function correlation coefficients by integrating the voltage and current signals at least once during each period of the power system and periodically sampling and holding the integrated signal in sequence with the integration. The present and a plurality of immediately preceding correlation coefficient values are stored in memory, and by combination of the correlation coefficients by addition, subtraction or multiplication, power system performance parameters, such as real power, reactive power, voltage, current, or power factor, are obtained for utilization in revenue metering or overload protection applications. Related methods are also disclosed.

Claims

1. A metering system for electronically metering an A.C. electrical power system of predetermined frequency to determine real and reactive power in the system, said metering system comprising:

voltage sensing means adapted to sense voltage in the power system, said voltage sensing means further adapted to provide an output signal proportional to said voltage;

current sensing means adapted to sense current in the power system, said current sensing means further adapted to provide an output signal proportional to said current;

first and second filtering means for separately sampling respective ones of said voltage and current output signals at least once during each period of said power system to develop respective Walsh function correlation coefficient output signals for each of said voltage and current output signals; and

combining means for combining said Walsh function correlation coefficient output signals to determine real and reactive power parameters of the power system.

2. A metering system as defined in claim 1 wherein said filtering means separately sample the respective voltage or current output signals a plurality of times during each period of said power system to develop a present and a plurality of immediately preceding Walsh function correlation coefficient signals during each power system period,

said metering system further comprising memory means for storing the present and a plurality of immediately preceding Walsh function correlation coefficient signals;

said combining means adapted to combine the present and the plurality of immediately preceding Walsh function correlation coefficient signals to determine said power system parameters.

3. A metering system as defined in claim 2 further comprising multiplexing means interposed between a plurality of said filtering means and said memory means for multiplexing a plurality of said Walsh function correlation coefficient signals from said plurality of filtering means to a single memory means.

4. A metering system as defined in claim 2 further comprising analog-to-digital conversion means interposed between said filtering means and said memory means for converting each of said Walsh function correlation coefficient signals from an analog form to a digital signal before storage of the digital signals in said memory means.

5. A metering system as defined in claim 4 wherein said memory means and said combining means comprise digital processor means for storing each successive digital signal from said analog-to-digital conversion means, said digital processor means further selectively positively or negatively adding a present and a plurality of immediately preceding digital signals to thereby determine said real and reactive power parameters of the power system.

6. A metering system as defined in claim 1 further comprising display means for displaying said power system parameter determined by said metering system.

7. A metering system as defined in claim 1 further comprising control means responsive to any irregularity in the power system parameter determined by said metering system said control means further adapted to interrupt said power system upon the occurrence of said iregularity.

8. A metering system as defined in claim 1 wherein said filtering means comprises:

separate low-pass filter means for separately filtering frequencies higher than the power system frequency from each of said voltage and current output signals to provide respective filtered voltage and current output signals; and

sample and hold means for periodically sampling each filtered voltage and current output signal from each of said low-pass filter means at least once during each period of said power system to provide respective sampled voltage and current output signals, said sample and hold means holding the sampled output signals for a predetermined time interval.

9. A metering system for electronically metering an A.C. electrical power system of predetermined frequency to determine real and reactive power in the system, said system further including voltage sensing means for sensing voltage in the power system and providing a voltage output signal proportional to said voltage and current sensing means for sensing current in the power system and providing a current output signal proportional to the current in the power system, said metering system comprising:

filtering means for separately sampling respective ones of said voltage and current output signals at least once during each period of said power system to develop respective Walsh function correlation coefficient output signals for each of said voltage and current output signals, said filtering means including;

first and second integrating means responsive to respective output signals of said voltage and current sensing means for integrating the voltage and current output signals therefrom at least once during each period of said power system, each of said integrating means providing a respective integrated output signal;

sample and hold means for periodically and independently sampling the integrated output signals of said first and second integrating means, said sample and hold means further providing a sampled output signal and holding said sampled output signal for a predetermined time interval;

resetting means for resetting said first and second integrating means to initial conditions after sampling said respective integrated output signals; and

said metering system further comprising combining means for combining said Walsh function correlation coefficient output signals to determine real and reactive power parameters of the power system.

10. A method of metering an A.C. electrical power system to determine real and reactive power parameters therein, said power system including voltage sensing means for sensing voltage in the power system and providing at least one voltage output signal proportional to voltage in said system, said system further including current sensing means for sensing current in the power system and providing at least one current output signal proportional to current in said system, said method comprising the steps of:

filtering said at least one voltage output signal with a finite-duration impulse-response filter at least once during each period of the power system to periodically develop a Walsh function correlation coefficient output signal for each of said at least one voltage output signal;

filtering said at least one current output signal with a finite-duration impulse-response filter at least once during each period of the power system to periodically develop a Walsh function correlation coefficient output signal for each of said at least one current output signal;

storing the periodically developed Walsh function correlation coefficient voltage and current output signals in a memory means; and

combining a present and a plurality of immediately preceding Walsh function correlation coefficient voltage and current output signals in said memory means to determine real and reactive parameters of the power system.

11. A method as defined in claim 10 wherein filtering by finite-duration impulse-response filters includes the steps of:

separately low-pass filtering respective ones of said voltage and current output signals with separate low-pass filter means to filter frequencies significantly higher than said predetermined power system frequency from respective ones of said voltage and current output signals, said filter means providing respective filtered voltage and current output signals;

sampling and holding respective ones of the filtered voltage and current output signals from said low-pass filter means at least once during each period of said power system for providing respective sampled voltage and current output signals; and

holding respective ones of the sampled output signals for a predetermined time interval.

12. A method as defined in claim 10 further comprising an additional step of multiplexing each of said sampled voltage and current output signals from each finite-duration impulse-response filter with multiplexer means for storage of said sampled output signals in a single memory means.

13. A method as defined in claim 12 comprising an additional step of successively converting multiplexed signals from said multiplexer means from an analog form to a digital form before storing the converted digital signals in said memory means.

14. A method as defined in claim 13 comprising an additional step of interrupting said power system by a relay means interposed in said power system and responsive to the digital signals stored in said memory means when said signals indicate the existence of an overcurrent or fault condition in said power system.

15. An overcurrent relay for responding to an overcurrent or fault condition in an A.C. electrical power system to interrupt said power system upon the occurrence of said overcurrent or fault condition, said overcurrent relay comprising:

current sensing means adapted to sense current in the power system, said current sensing means further adapted to provide an output signal proportional to said current;

filtering means for sampling said current output signal at least once during each period of said power system to develop a Walsh function correlation coefficient output signal for said current output signal;

memory means for storing a present and a plurality of immediately preceding Walsh function correlation coefficient signals;

combining means adapted to combine the present and the plurality of immediately preceding Walsh function correlation coefficient signals to determine a power system parameter; and

relay means interposed in said power system and responsive to the power system parameter determined by said combining means to interrupt said power system when said power system parameter indicates the existence of an overcurrent or a fault condition.

16. An overcurrent relay as defined in claim 15 further comprising analog-to-digital conversion means interposed between said filter means and said memory means for converting said Walsh function correlation coefficient signals from an analog form to a digital signal before storage of the digital signals in said memory means.

17. An overcurrent relay as defined in claim 16 wherein said memory means and said combining means comprise digital processor means for storing each successive digital signal from said analog-to-digital conversion means, said digital processor means further selectively positively or negatively adding a present and a plurality of immediately preceding digital signals to thereby determine said power system parameter.

18. A metering system for electronically metering an A.C. electrical power system of predetermined frequency to determine real and reactive power in the system, said metering system comprising:

voltage sensing means adapted to sense voltage in the power system, said voltage sensing means further adapted to provide an output signal proportional to said voltage;

current sensing means adapted to sense current in the power system, said current sensing means further adapted to provide an output signal proportional to said current;

first and second filtering means for separately sampling respective ones of said voltage and current output signals at least once during each period of said power system to develop respective Walsh function correlation coefficient output signals for each of said voltage and current output signals;

said filtering means including first and second integrating means responsive to respective output signals of said voltage and current sensing means for integrating the voltage and current output signals therefrom at least once during each period of said power system, each of said integrating means providing a respective integrated output signal,

sample and hold means for periodically and independently sampling said integrated output signals, said sample and hold means further providing a sampled output signal and holding said sampled output signal for a predetermined time interval, and

resetting means for resetting said integrating means to initial conditions after sampling said respective integrated output signals; and

combining means for combining said Walsh function correlation coefficient output signals to determine the real and reactive power parameters of the power system.

19. A metering system as defined in claim 18 wherein said filtering means further comprise:

analog memory means for storing a present and a predetermined number of immediately preceding sampled voltage and current output signals from said sample and hold means; and

a plurality of summing amplifiers for positively or negatively summing each of the present and immediately preceding sampled output signals in said analog memory means, said summing amplifiers each providing a signal related in magnitude to a Walsh function correlation coefficient of the voltage or current in said power system.

20. A metering system for electronically metering an A.C. electrical power system of predetermined frequency to determine real and reactive power in the system, said metering system comprising:

voltage sensing means adapted to sense voltage in the power system, said voltage sensing means further adapted to provide an output signal proportional to said voltage;

current sensing means adapted to sense current in the power system, said current sensing means further adapted to provide an output signal proportional to said current;

first and second filtering means for separately sampling respective ones of said voltage and current output signals at least once during each period of said power system to develop respective Walsh function correlation coefficient output signals for each of said voltage and current output signals;

combining means comprising a plurality of analog multiplier means, said analog multiplier means each multiplying a pair of said Walsh function correlation coefficient output signals from said filtering means and providing an output signal related in magnitude to the pairs of multiplied Walsh function correlation coefficient output signals; and

summing and scaling amplifier means for positively or negatively summing each of the output signals of said analog multiplier means and for scaling the resultant sum by an appropriate gain factor to provide an output signal related in magnitude to the real or reactive power in the system.

21. A method of metering an A.C. electrical power system to determine real and reactive power parameters therein, said power system including voltage sensing means for sensing voltage in the power system and providing at least one voltage output signal proportional to voltage in said system, said system further including current sensing means for sensing current in the power system and providing at least one current output signal proportional to current in said system, said method comprising the steps of:

filtering said at least one voltage output signal with a finite-duration impulse-response filter at least once during each period of the power system to periodically develop a Walsh function correlation coefficient output signal for each of said at least one voltage output signal;

filtering said at least one current output signal with a finite-duration impulse-response filter at least once during each period of the power system to periodically develop a Walsh function correlation coefficient output signal for each of said at least one current output signal;

said filtering including separately integrating respective ones of said voltage and current output signals with respective first and second integrating means at least once during each period of said power system, said first and second integrating means providing respective integrated voltage and current output signals,

separately and periodically sampling each integrated voltage and current output signal with sample and hold means for providing respective sampled voltage and current output signals,

holding each of the sampled voltage and current output signals with holding means for a predetermined time interval, and

resetting each of said first and second integrating means to initial conditions after sampling each of said integrated voltage and current output signals;

storing the periodically developed Walsh function correlation coefficient voltage and current output signals in a memory means; and

combining a present and a plurality of immediately preceding Walsh function correlation coefficient voltage and current output signals in said memory means to determine real and reactive parameters of the power system.

22. An overcurrent relay for responding to an overcurrent or fault condition in an A.C. electrical power system to interrupt said power system upon the occurrence of said overcurrent or fault condition, said overcurrent relay comprising:

current sensing means adapted to sense current in the power system, said current sensing means further adapted to provide an output signal proportional to said current;

filtering means for sampling said current output signal at least once during each period of said power system to develop a Walsh function correlation coefficient output signal for said current output signal;

said filtering means comprising integrating means responsive to the output signal of said current sensing means for integrating the current output signal therefrom at least once during each period of said power system, said integrating means providing an integrated output signal,

sample and hold means for periodically sampling the integrated output signal of said integrating means, said sample and hold means further providing a sampled output signal and holding said sampled output signal for a predetermined time interval, and

resetting means for resetting said integrating means to initial conditions after sampling said integrated output signal;

memory means for storing a present and a plurality of immediately preceding Walsh function correlation coefficient signals;

combining means adapted to combine the present and the plurality of immediately preceding Walsh function correlation coefficient signals to determine a power system parameter; and

relay means interposed in said power system and responsive to the power system parameter determined by said combining means to interrupt said power system when said power system parameter indicates the existence of an overcurrent or a fault condition.