On-line calibration and compensation of a current transformer

Patent metadata

Field	Value
Publication number	US-10345419-B2
Application number	US-201514977103-A
Country	US
Kind code	B2
Filing date	Dec 21, 2015
Priority date	Dec 21, 2015
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

Systems and methods are disclosed for calibration and compensation of on-line current transformers. In certain embodiments, a method to calibrate a single current transformer by use of an AC injected current is provided. In other embodiments, a method to calibrate and compensate multiple current transformers using a single AC injected current is provided. In further embodiments, a system for calibration and compensation of multiple current transformers is provided. The adequate frequency of the injected current as well as other characteristics for adequate use in some embodiments is provided.

First claim

The invention claimed is:

1. A method comprising:
measuring voltage data received from a current transformer, including a magnetic core, while on-line, the voltage data measured by an electronic system including a processor configured to generate calibration data and compensation of differential currents, the electronic system coupled to the current transformer through which a first current I L at a first frequency f L and a second current I i at a second frequency f C flows, wherein the second current is known and further wherein the second frequency differs from the first frequency and the first current is an AC load current;
separating, by the electronic system, at least two spectral components present in the voltage data;
determining, by the electronic system, a first spectral component V OL associated with the first frequency;
determining, by the electronic system, a second spectral component V OC associated with the second frequency;
calibrating, by the electronic system, a gain g for the current transformer from the known second current and the V OC , where g=V OC /I i ;
determining, by electronic system, a compensation for a measurement of the first current, where the compensation is determined as:
I L =V OC f C N P /gfL

where N P is a number of winding turns of a winding through which the second current flows, and;
providing, by the electronic system, the compensation to the magnetic current transformer, the provision causing the magnetic current transformer to compensate the measurement of the first current with respect to the determined compensation.

2. The method of claim 1 , further comprising compensating a measurement of the first current based at least on the calibrated gain.

3. The method of claim 1 , wherein the act of separating the at least two spectral components comprises processing the voltage data with a digital signal processor to spectrally separate the voltage data.

4. The method of claim 3 , wherein the digital signal processor applies a Fast Fourier Transform to spectrally separate the voltage data.

5. The method of claim 1 , wherein the act of separating the at least two spectral components comprises processing the voltage data through an analog filter bank.

6. The method of claim 1 , wherein the first current is carried through a pair of load cables.

7. The method of claim 1 , wherein the second current is a known injected current generated by a current injector.

8. A method comprising:
measuring a first voltage data received from a first current transformer, including a magnetic core, while on-line, the voltage data measured by an electronic system including a processor configured to generate calibration data and compensation of differential currents, the electronic system coupled to the first magnetic current transformer through which a first AC load current I L at a first frequency f L and an AC injected current I i at a second frequency f C flows, wherein the injected current is known and the second frequency differs from the first frequency;
measuring a second voltage data received from a second current transformer, including a magnetic core, while on-line, the second voltage data measured by the electronic system coupled to the second magnetic current transformer through which a second AC load current at a third frequency and the injected current flows, wherein the third frequency differs from the second frequency and the third frequency may be equal to the first frequency;
separating, by the electronic system, the plurality of voltage data into spectral components;
determining, by the electronic system, an injected current spectral component V OC associated with the second frequency;
determining, by the electronic system, a first spectral component V OL based on the first frequency from the first voltage data;
determining, by the electronic system, a second spectral component based on the third frequency from the second voltage data;
calibrating, by the electronic system, a gain g from the known AC injected current and the V OC , where g=V OC /I i ;
determining, by the electronic system, a compensation for a measurement of one or both of the first AC load current or the second AC load current based at least on the calibrated gain;
wherein the first AC load current and the second AC load current are respectively carried through first and second paired load cables; and
wherein the compensation is determined as:
I L =V OC f C N P /gfL

wherein N P is a number of winding turns of a winding through which the AC injected current flows, and;
providing, by the electronic system, the compensation to the magnetic current transformer, the provision causing the magnetic current transformer to compensate the one or both of the first AC load current or the second AC load current with respect to the determined compensation.

9. The method of claim 8 , wherein the act of separating the spectral components comprises processing the voltage data with a digital signal processor to spectrally separate the voltage data.

10. The method of claim 9 , wherein the digital signal processor applies a Fast Fourier Transform to spectrally separate the voltage data.

11. The method of claim 9 , wherein the digital signal processor applies a Wavelet Transform to spectrally separate the voltage data.

12. The method of claim 8 , wherein the act of separating the spectral components comprises processing the voltage data through an analog filter bank.

13. The method of claim 12 , wherein the analog filter bank comprises at least a low pass filter and a high pass filter.

Assignees

• Gen Electric

Inventors

• Neti Prabhakar
• Younsi Karim
• Lu Dan Tho

Classifications

• G01R15/18

  using inductive devices, e.g. transformers · CPC title

• G01R35/005 Primary

  Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references (G01R33/0035, G01R35/002 take precedence) · CPC title

• G01R19/0092

  Measuring current only · CPC title

• G01R35/00 Primary

  Testing or calibrating of apparatus covered by the other groups of this subclass · CPC title