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

• US 7,660,682 B2
• Filed: 11/30/2007
• Issued: 02/09/2010
• 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:
  US11/998,736
• Publication Number:
  US 20080125986A1
• Time in Patent Office: 802 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 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,

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 at least one calibration factor for the at least one external potential transformer (PT) is determined from one voltage test point.

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 the greater the nonlinearity of the errors, the greater the concentration of test points.

4. 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.

5. 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,

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 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.

6. 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,

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.

7. The method according to claim 6, wherein the greater the non-linearity of errors, the greater the concentration of test points.

8. The method according to claim 6, 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.

9. 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 current and voltage signals operated on by the at least one external CT and the at least one external PT, respectively,

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.

10. The meter device according to claim 9, 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.

11. 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,

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, and

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.

12. The meter device according to claim 11, 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.

13. The meter device according to claim 11, 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.

14. The meter device according to claim 11, wherein 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.