Electronic electricity meter configured to correct for transformer inaccuracies

• US 20020180420A1
• Filed: 06/01/2001
• Published: 12/05/2002
• Est. Priority Date: 06/01/2001
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Lee, Robert Edward Jr., Elmore, David D., Lavoie, Gregory P., Schmidt, Larry A.
• Granted Patent: US 6,636,028 B2
• Time in Patent Office: Days
• US Class Current: 324/142
• CPC Class Codes: G01R 21/133 by using digital technique

Abstract

The present invention, in one embodiment, is an electronic electricity meter which includes voltage sensors configured to generate measurements of voltage at voltage elements, current sensors configured to generate measurements of current through current elements, a microcomputer coupled to the current and voltage sensors and configured to control operation of the meter, and a memory coupled to the microcomputer including calibration constants to compensate for instrument transformer ratio and phase angle errors, the microcomputer configured to use the calibration constants, when so instructed, to correct for measurement errors that occur based upon instrument transformer ratios and phase angles, to correct metering quantities calculated by the microcomputer.

Claims

1. An electronic electricity meter comprising:

voltage sensors configured to generate measurements of voltage at voltage elements;

current sensors configured to generate measurements of current through current elements;

a microcomputer coupled to the current and voltage sensors and configured to control operation of said meter; and

a memory coupled to said microcomputer and configured to store configuration and metering data, said memory further comprising calibration constants to compensate for instrument transformer ratio and phase angle errors, said microcomputer configured to use said calibration constants, when so instructed, to correct for measurement errors that occur based upon instrument transformer ratios and phase angles, to correct metering quantities calculated by said microcomputer.

2. An electronic electricity meter according to claim 1 wherein said calibration constants are enabled via a software switch stored in said memory.

3. An electronic electricity meter according to claim 1 wherein said memory comprises:

an instrument transformer ratio correction factor for voltage;

an instrument transformer ratio correction factor for current;

a factory calibration gain coefficient for each voltage and current element;

a determined instrument transformer gain coefficient for each voltage and current element;

an instrument transformer phase angle error for voltage;

an instrument transformer phase angle error for current;

a factory calibration phase correction for each voltage and current element;

a calculated instrument transformer phase correction for each voltage and current element;

a phase correction angle for each voltage and current element; and

an instrument transformer phase correction angle for each voltage and current element.

4. An electronic electricity meter according to claim 3 wherein said instrument transformer gain coefficient for each voltage and current element is determined by the instrument transformer ratio correction factor for the element×

a factory calibration gain coefficient.

5. An electronic electricity meter according to claim 3 wherein said instrument transformer phase correction angle for each voltage and current element is determined as a phase correction angle—

the instrument transformer phase angle error, where the phase correction angle is calculated as PCA_old=A TAN {(K_old−

(1/K_old))×

SIN(ω

T_s)/[2+(K_old+(1/K_old))×

COS(ω

T_s), where ω

T_s=2π

(F_line/F_sampling) and K_old=a factory calibration phase correction/2¹⁵, for each voltage and current element.

6. An electronic electricity meter according to claim 5 wherein said instrument transformer phase correction for each voltage and current element is determined as PC_new=2¹⁵×

(SIN(ω

T_s)+SIN(PCA_new)/SIN(ω

T_s−

PCA_new)), where PCA_new is the instrument transformer phase correction angle for each voltage and current element.

7. An electronic electricity meter according to claim 5 wherein F_line is equal to one of 50 Hz or 60 Hz and F_sampling is equal to 3281.25 Hz.

8. An electronic electricity meter according to claim 1 wherein said memory is at least one of flash memory or electrically erasable programmable read only memory.

9. A method for compensating for instrument transformer induced measurement errors in an electronic electricity meter, the meter including current sensors configured to measure current through current elements, voltage sensors configured to measure voltage at voltage elements, a microcomputer coupled to the current and voltage sensors and configured to control operation of the meter, and a memory coupled to the microcomputer and configured to store configuration and metering data, said method comprising the steps of:

configuring the memory with calibration constants to compensate for instrument transformer induced ratio and phase angle errors;

enabling the calibration constants via a software switch stored in the memory; and

correcting measured metering quantities calculated by the microcomputer using the calibration constants.

10. A method according to claim 9 wherein said step of configuring the memory with calibration constants comprises the steps of:

calculating an instrument transformer gain coefficient for each voltage and current element;

calculating an instrument transformer phase correction angle for each voltage and current element;

calculating an instrument transformer phase correction for each voltage and current element; and

storing the calculated coefficients in the memory.

11. A method according to claim 10 wherein the instrument transformer gain coefficient for each voltage and current element is calculated as an instrument transformer ratio correction factor×

a factory calibration gain coefficient for each voltage and current element.

12. A method according to claim 11 wherein the instrument transformer ratio correction factor is one of a voltage correction factor or a current correction factor.

13. A method according to claim 10 wherein instrument transformer phase correction angle for each voltage and current element is calculated as a meter phase correction angle for each voltage and current element—

an instrument transformer phase angle error.

14. A method according to claim 13 wherein the instrument transformer phase angle error is one of a voltage transformer phase angle error and a current phase angle error.

15. A method according to claim 13 wherein the meter phase correction angle for each voltage and current element is calculated as PCA_old=A TAN{(K_old−

(1/K_old))×

SIN(ω

T_s)/[2+(K_old+(1/K_old))×

COS(ω

T_s), where ω

T_s=2π

(F_line/F_sampling) and K_old=a factory calibration phase correction for each voltage and current element/2¹⁵.

16. A method according to claim 13 wherein the instrument transformer phase correction for each voltage and current element is calculated as PC_new=2¹⁵×

(SIN(ω

T_s)+SIN(PCA_new)/SIN(ω

T_s−

PCA_new)), where PCA_new is the instrument transformer phase correction angle for each voltage and current element and ω

T_s=2π

(F_line/F_sampling).

18. An electronic electricity meter according to claim 17 wherein the calculated instrument transformer gain coefficient for each voltage and current element in said meter is calculated as an instrument transformer ratio correction factor×

a factory calibration gain coefficient for each voltage and current element in said meter.

19. An electronic electricity meter according to claim 17 wherein the instrument transformer phase correction for each voltage and current element in said meter is determined by the relationship 2¹⁵×

(SIN(ω

T_s)+SIN(PCA_new)/SIN(ω

T_s−

PCA_new)), where ω

T_s=2π

(F_line/F_sampling) and PCA_new is the instrument transformer phase correction angle for each voltage and current element, which is calculated as PCA_old−

an instrument transformer phase angle error, where PCA_old=A TAN{(K_old−

(1/K_old))×

SIN(ω

T_s)/[2+(K_old+(1/K_old))×

COS(ω

T_s), where ω

T_s=2π

(F_line/F_sampling) and K_old=a factory calibration phase correction for each voltage and current element/2¹⁵.

17. An electronic electricity meter configured to:

store a set of calibration constants in a non-volatile memory of said meter for instrument transformer ratio and phase angle error compensation;

store a software switch for enabling or disabling the instrument transformer ratio and phase angle compensation in said meter; and

meter a plurality of electrical quantities of a power source;

and said meter having a microcomputer configured to selectively employ error compensation values, based on a value of the software switch and the calibration constants, the calibration constants configured to compensate for errors by instrument transformers, the calibration constants comprising at least one of a calculated instrument transformer gain coefficient for each voltage and current element in said meter, and an instrument transformer phase correction for each voltage and current element in said meter.

20. A processor for use in an electronic electricity meter, said processor configured to use calibration constants to compensate for instrument transformer ratio and phase angle errors, said calibration constants comprising:

a determined instrument transformer gain coefficient for each voltage and current element in the meter; and

an instrument transformer phase correction for each voltage and current element in the meter.

21. A processor according to claim 20 wherein said calculated instrument transformer gain coefficient is calculated as an instrument transformer ratio correction factor×

a factory calibration gain coefficient for each voltage and current element in said meter.

22. A processor according to claim 20 wherein said instrument transformer phase correction is determined by the relationship 2¹⁵×

(SIN(ω

T_s)+SIN(PCA_new)/SIN(ω

T_s−

PCA_new)), wherein said processor further configured to calculate ω

T_s as 2π

(F_line/F_sampling) and PCA_new as PCA_old−

an instrument transformer phase angle error, where PCA_old=A TAN{(K_old−

(1/K_old))×

SIN(ω

T_s)/[2+(K_old+(1/K_old))×

COS(ω

T_s), where K_old=a factory calibration phase correction for each voltage and current element/2¹⁵.

23. A processor according to claim 22 wherein F_line is one of 50 Hz or 60 Hz and F_sampling is 3281.25 Hz.