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

• US 8,073,642 B2
• Filed: 02/08/2010
• Issued: 12/06/2011
• Est. Priority Date: 10/18/2004
• Status: Active Grant

• Current Assignee: Electro Industries/Gaugetech
• Original Assignee: Electro Industries/Gaugetech
• Inventors: Slota, Frederick B., Werner, Andrew J.
• Primary Examiner(s): WACHSMAN, HAL D
• Application Number:
  US12/701,921
• Publication Number:
  US 20100145642A1
• Time in Patent Office: 666 Days
• Field of Search: 702/57, 702/60, 702/61, 702/62, 702/64, 702/65
• US Class Current: 702/57
• 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 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 external current transformer (CT) and at least one external 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 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 external CT, at least one calibration factor corresponds to each test point and the at least one calibration factor for the at least one external PT being determined from one voltage test point; and

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

2. The method 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 predetermined non-zero 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.

3. The method according to claim 2, 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.

4. A method for calibrating a meter device for measuring electrical energy comprising the steps of

receiving information relating to at least one error, each 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 current external 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;

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

uploading generated calibration factors to the meter device;

wherein;

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

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 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 test points compensate for non-linearity of the at least one error associated with the range of input current values and the at least one calibration factor for the at least one external PT being determined from one voltage test point.

5. The method according to claim 4, wherein the receiving step includes receiving the information from at least one of a user input device, the meter device, equipment providing the power 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.

6. The method according to claim 4, further comprising the step of performing a test comprising the step of generating 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).

7. The method according to claim 6, the step of performing a test further comprising the step of determining a selected input value for performing the test.

8. The method according to claim 6, wherein performing the test step further comprises steps of:

performing at least one of a first, second and third test, wherein;

the performing the first test step comprises the step of testing at least one test point comprising the step of controlling the equipment for the input value to have a predetermined voltage;

the performing the second test step comprises the step of testing a first series of test points comprising the step of controlling 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

the performing the third test step comprises the step of testing a second series of test points comprising the step of controlling 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.

9. The method according to claim 8, wherein the step of performing the first test is followed by the step of performing the second test, which is followed by the step of performing the third test.

10. The method according to claim 8, wherein after testing a single test point of one of the at least one test point, the first series of test points, and the second series of test points, the steps of generating the calibration factor and uploading are performed, wherein the calibration factor generated corresponds to the error related to the input value used for the single test point.

11. The method according to claim 8, wherein after testing each of at least two test points of the one of the at least one test point, the first series of test points, and the second series of test points, the steps of generating the at least one calibration factor and uploading are performed, wherein the at least one calibration factor generated for each respective test point of the at least two test points corresponds to the error related to the input value used for the respective test point.

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

programming in the meter 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 electrical energy provided to the meter, 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 and wherein the greater the non-linearity of the errors, the greater the concentration of test points and the at least one calibration factor for the at least one external PT being determined from one voltage test point; 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.

13. The method of claim 12, wherein the at least one calibration factor includes at least two calibration factors.

14. The method of claim 12, wherein the at least one calibration factor includes at least three calibration factors.

15. The method of claim 12, wherein the meter is programmed via a keypad disposed on the meter.

16. The method of claim 12, wherein the meter is programmed via an external processing device.