System and method for compensating for potential and current transformers in energy meters

• US 20080125986A1
• Filed: 11/30/2007
• Published: 05/29/2008
• Est. Priority Date: 10/18/2004
• Status: Active Grant

• Current Assignee: Electro Industries/Gaugetech
• Original Assignee: Electro Industries/Gaugetech
• Inventors: Werner, Andrew J., Slota, Frederick Blair
• Granted Patent: US 7,660,682 B2
• Time in Patent Office: Days
• US Class Current: 702/61
• CPC Class Codes: G01R 22/06 by electronic methods
• CPC Class Codes: G01R 35/04 of instruments for measuring time integral of power or current

Abstract

A meter device for measuring electrical energy is provided. The meter device includes circuitry for measuring at least one parameter of electrical energy provided to the meter device. A storage device is provided for storing at least one calibration factor for compensating for errors associated with at least one of at least one external current transformer (CT) and at least one external potential transformer (PT) that operates on the electrical energy provided to the meter device. At least one processor is provided for processing the at least one calibration factor for adjusting the measuring for compensating for the errors when measuring the at least one parameter of electrical energy.

Claims

1. A meter device for measuring electrical energy comprising:

circuitry for measuring at least one parameter of electrical energy monitored by the meter device;

a storage device for storing at least one calibration factor for compensating for errors associated with at least one of at least one external current transformer (CT) and at least one external potential transformer (PT) that operates on the electrical energy provided to the meter device;

at least one processor for processing the at least one calibration factor for adjusting the measured at least one parameter of electrical energy for compensating for the errors when measuring the at least one parameter of electrical energy; and

at least one communication port for receiving the at least one calibration factor from an external device.

2. The meter device according to claim 1, wherein the at least one calibration factor is selected from the group consisting of at least one voltage gain calibration factor for compensating for errors associated with the at least one external PT;

at least one current gain calibration factor for compensating for errors associated with the at least one external CT when current and voltage signals of the electrical energy operated on by the at least one external CT and the at least one external PT, respectively, are in phase; and

at least one phase calibration factor for compensating for errors associated with the at least one external CT with a phase shift of sixty degrees with respect to the current and voltage signals operated on by the at least one external CT and the at least one external PT, respectively.

3. The meter device according to claim 1, wherein calibration factors of the at least one calibration factor correct for errors measured during testing of respective test points of a series of test points, each test point corresponding to a different current magnitude for modeling non-linearity of errors associated with a range of current magnitudes for current signals of the electrical energy operated on by the at least one external CT, and at least one calibration factor corresponds to each test point.

4. The meter device according to claim 3, wherein the greater the non-linearity of the errors, the greater the concentration of test points.

5. The meter device according to claim 3, wherein at least one calibration factor for the at least one PT is determined from one voltage test point.

6. The meter device according to claim 3, a plurality of phase calibration factors are provided, each phase calibration factor corresponding to a test point of the series of test points, wherein compensating for errors when measuring power of the at least one parameter of electrical energy in which measured current associated with the measured power falls in between two test points includes using a calibration factor related to a calibration factor corresponding to at least one of the two test points.

7. The meter device according to claim 1, wherein the at least one communication port is further configured for communicating with the at least one processor.

8. A method for measuring electrical energy in a meter comprising the steps of:

storing at least one calibration factor for compensating for errors associated with at least one of at least one current transformer (CT) and at least one potential transformer (PT) that operates on electrical energy provided to the meter; and

measuring at least one electrical parameter of the electrical energy provided to the meter device comprising the step of;

adjusting the measuring for compensating for the errors by processing the measured at least one electrical parameter using the at least one calibration factor;

wherein calibration factors of the at least one calibration factor correct for errors measured during testing of respective test points of a series of test points, each test point corresponding to a different current magnitude for modeling non-linearity of errors associated with a range of current magnitudes for current signals of the electrical energy operated on by the at least one CT, and at least one calibration factor corresponds to each test point.

9. The method according to claim 8, wherein the greater the non-linearity of errors, the greater the concentration of test points.

10. The method according to claim 8, wherein the at least one calibration factor is selected from the group consisting of at least one voltage gain calibration factor for compensating for errors associated with the at least one PT;

at least one current gain calibration factor for compensating for errors associated with the at least one CT when current and voltage signals of the electrical energy operated on by the at least one CT and the at least one PT, respectively, are in phase; and

at least one phase calibration factor for compensating for errors associated with the at least one CT with a predetermined non-zero phase shift with respect to the current and voltage signals operated on by the at least one CT and the at least one PT, respectively.

11. The method according to claim 10, wherein compensation is performed by at least one of implementing the at least one voltage gain calibration factor as a divisive factor, implementing the at least one current gain calibration factor as a multiplicative factor, and shifting a measured phase angle of the at least one electrical parameter in accordance with the phase calibration factor:

(the predetermined non-zero phase shift)−

(cos<sup>−

1</sup>(50/(100+y))), where “

y”

is the difference between the measured phase angle and an expected phase angle, expressed in terms of percentage.

12. A meter device for measuring electrical energy comprising:

circuitry for measuring at least one parameter of electrical energy provided to the meter device;

a storage device for storing at least one calibration factor for compensating for errors associated with at least one of at least one external current transformer (CT) and at least one external potential transformer (PT) that operates on the electrical energy provided to the meter device; and

at least one processor for processing the at least one calibration factor for adjusting the measuring for compensating for the errors when measuring the at least one parameter of electrical energy, wherein the at least one calibration factor includes at least one phase calibration factor for compensating for errors associated with the at least one external CT with a predetermined phase shift with respect to the current and voltage signals operated on by the at least one external CT and the at least one external PT, respectively.

13. The meter device according to claim 12, wherein during testing for determining errors corresponding to the at least one external CT and the at least one external PT, if it is determined that a power reading is “

y”

percent below an expected value, then the phase shift is adjusted by shifting the at least one phase calibration factor (having a default value of 0 degrees) by an additional (cos<sup>−

1</sup>(50/(100+y))) degrees.

14. The meter device according to claim 12, wherein the at least one calibration factor further includes at least one voltage gain calibration factor for compensating for errors associated with the at least one external PT, and at least one current gain calibration factor for compensating for errors associated with the at least one external CT when current and voltage signals of the electrical energy operated on by the at least one external CT and the at least one external PT, respectively, are in phase.

15. The meter device according to claim 14, wherein calibration factors of the at least one calibration factor correct for errors measured during testing of respective test points of a series of test points, each test point corresponding to a different current magnitude for modeling non-linearity of errors associated with a range of current magnitudes for current signals of the electrical energy operated on by the at least one external CT, and at least one calibration factor.

16. The meter device according to claim 15, wherein the greater the non-linearity of the errors, the greater the concentration of test points, and wherein the non-linearity is greater at current levels less than 5 amps.

17. The meter device according to claim 15, wherein a plurality of current gain calibration factors are provided, each current gain calibration factor corresponding to a test point of the series of test points, wherein compensating for errors when measured current of the at least one parameter of electrical energy falls in between two test points includes using a calibration factor related to a calibration factor corresponding to at least one of the two test points.

18. The meter device according to claim 15, a plurality of phase calibration factors are provided, each phase calibration factor corresponding to a test point of the series of test points, wherein compensating for errors when measuring power of the at least one parameter of electrical energy in which measured current associated with the measured power falls in between two test points includes using a calibration factor related to a calibration factor corresponding to at least one of the two test points.

19. A method for measuring electrical energy in a meter comprising the steps of:

storing at least one calibration factor for compensating for errors associated with at least one of at least one current transformer (CT) and at least one potential transformer (PT) that operates on electrical energy provided to the meter; and

measuring at least one electrical parameter of the electrical energy provided to the meter device comprising the step of;

adjusting the measuring for compensating for the errors by processing the measured at least one electrical parameter using the at least one calibration factor;

wherein calibration factors of the at least one calibration factor correct for errors measured during testing of respective test points of a series of test points, each test point corresponding to a different current magnitude for modeling non-linearity of errors associated with a range of current magnitudes for current signals of the electrical energy operated on by the at least one CT, and at least one calibration factor corresponds to each test point; and

wherein the greater the non-linearity of the errors, the greater the concentration of test points.

20. The method according to claim 19, wherein the at least one calibration factor is selected from the group consisting of at least one voltage gain calibration factor for compensating for errors associated with the at least one PT;

at least one current gain calibration factor for compensating for errors associated with the at least one CT when current and voltage signals of the electrical energy operated on by the at least one CT and the at least one PT, respectively, are in phase; and

at least one phase calibration factor for compensating for errors associated with the at least one CT with a predetermined non-zero phase shift with respect to the current and voltage signals operated on by the at least one CT and the at least one PT, respectively.

21. The method according to claim 20, wherein compensation is performed by at least one of implementing the at least one voltage gain calibration factor as a divisive factor, implementing the at least one current gain calibration factor as a multiplicative factor, and shifting a measured phase angle of the at least one electrical parameter in accordance with the phase calibration factor:

(the predetermined non-zero phase shift)−

(cos<sup>−

1</sup>(50/(100+y))), where “

y”

is the difference between the measured phase angle and an expected phase angle, expressed in terms of percentage.

22. A processing device in communication with a meter device for measuring electrical energy, the processing device comprising:

an input device for receiving input information relating to at least one error, an error of the at least one error related to a difference between an input value corresponding to at least one of voltage, current, and phase shift therebetween associated with electrical energy operated on by at least one of at least one external current transformer (CT) and at least one external potential transformer (PT) which is provided to the meter device, and a value measured by the meter device which corresponds to the input value;

at least one processor for generating at least one calibration factor, each calibration factor corresponding to an error of the at least one error for adjusting measurement by the meter device in accordance with the error; and

at least one communication device for uploading generated calibration factors to the meter device.

23. The processing device according to claim 22, wherein the input information is received from the group consisting of a user input device, the meter device, equipment providing the electrical energy operated on by the at least one of the at least one external current transformer (CT) and the at least one external potential transformer (PT), and a control unit controlling the equipment.

24. The processing device according to claim 22, wherein the processing device generates control signals for controlling equipment providing the electrical energy operated on by the at least one of the at least one external current transformer (CT) and the at least one external potential transformer (PT) for providing a selected input value for performing a test.

25. The processing device according to claim 24, wherein the processing device determines the selected input value for performing the test.

26. The processing device according to claim 24, wherein the test comprises at least one of a first test including testing at least one test point in which the processing device controls the equipment for the input value to have a predetermined voltage;

a second test including a first series of test points in which the processing device controls the equipment for the input value to have a different predetermined current for respective test points of the first series of test points with the phase shift being zero degrees; and

a third test including a second series of test points in which the processing device controls the equipment for the input value to have a different predetermined current for respective test points of the second series of test points with the phase shift being sixty degrees.

27. The processing device according to claim 26, wherein after testing a single test point of one of the first series of test points and the second series of test points, the calibration factor corresponding to the at least one error related to the input value used for the single test point is determined and uploaded.

28. The processing device according to claim 26, wherein after testing each of at least two test points of the one of the first series of test points and the second series of test points, the calibration factor corresponding to the at least one error related to the input values used for the respective test point of the at least two test points is determined and uploaded.

29. The processing device according to claim 22, wherein:

the at least one error is determined by performing a test, including measuring energy associated with a series of at least two test points;

each test point of the series corresponds to a different input current value over a range of input current values of the electrical energy operated on by the at least one external CT;

for each test point of the series of at least two test points there is at least one corresponding calibration factor;

respective calibration factors provide for adjusting measurement by the meter device, including correcting for errors of the at least one error related to the input current values to which the respective test points correspond; and

the calibration factors corresponding to the respective test points compensate for non-linearity of the at least one error associated with the range of input current values.

30. The processing device according to claim 29, wherein the greater the non-linearity of the at least one error associated with the range of input current values, the greater the concentration of the series of at least two test points over the range of input current values.