Methods for detecting and classifying loads on AC lines

• US 20080048640A1
• Filed: 08/20/2007
• Published: 02/28/2008
• Est. Priority Date: 08/18/2006
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Original Assignee: United States Of America As Represented By The Secretary Of The Army (Government of the United States of America)
• Inventors: Hull, David, Cremona-Simmons, Peter
• Granted Patent: US 7,701,196 B2
• Time in Patent Office: Days
• US Class Current: 324/76.77
• CPC Class Codes: G01R 29/08 Measuring electromagnetic field characteristics
• CPC Class Codes: G01R 31/42 AC power supplies

Abstract

Methods for detecting and classifying loads on alternating current (AC) lines are provided. One such method includes the steps of placing an AC field sensor in AC electric and magnetic fields generated by an AC line, generating an electric field signal representative of the AC electric field received by the AC field sensor, generating a magnetic field signal representative of the AC magnetic field received by the AC field sensor, generating a relative phase signal representative of relative phase changes between the electric and magnetic fields, and processing the relative phase signal to detect and classify loads on the AC line. In another method, relative load vector signals representative of relative magnitude and phase changes in the magnetic field are generated and processed to detect and classify loads on the AC line.

Claims

1. A method of detecting and classifying loads on an alternating current (AC) line, comprising the steps of:

placing an AC field sensor in AC electric and magnetic fields generated by an AC line;

generating an electric field signal representative of the AC electric field received by the AC field sensor;

generating a magnetic field signal representative of the AC magnetic field received by the AC field sensor;

generating a relative phase change signal representative of relative phase changes in the AC electric and magnetic fields; and

processing the relative phase change signal to detect and classify loads on the AC line.

2. The method of claim 1, wherein the placing step comprises placing a combination AC electric and magnetic sensor in the AC electric and magnetic fields.

3. The method claim 1, wherein the AC line comprises an AC power line.

4. The method of claim 1, wherein the electric field and magnetic field signals are voltage signals.

5. The method of claim 1, wherein the step of generating a relative phase change signal comprises filtering the electric and magnetic field signals to reduce harmonics and broadband noise.

6. The method of claim 1, wherein the step of generating a relative phase change signal comprises generating the relative phase change signal using a peak detector circuit and a comparator algorithm.

7. The method of claim 1, wherein the step of generating a relative phase change signal comprises generating the relative phase change signal using a zero-crossing detector and a comparator algorithm.

8. The method of claim 1, wherein the step of generating a relative phase change signal comprises filtering an unfiltered relative phase change signal using a low pass filter to reduce jitter and other spurious spikes introduced into the unfiltered relative phase change signal.

9. The method of claim 1, wherein the step of generating a relative phase change signal comprises:

identifying a first peak time associated with a positive peak value of the electric field signal;

identifying a second time associated with a positive peak value of the magnetic field signal;

subtracting the first and second peak times to obtain a time difference; and

converting the time difference into degrees to determine a phase difference between the electric and magnetic field signals.

10. The method of claim 1, wherein the step of generating a relative phase change signal comprises generating the relative phase change signal using a Fast Fourier Transform technique.

11. A method of detecting and classifying loads on an alternating current (AC) line, comprising the steps of:

placing an AC field sensor in AC electric and magnetic fields generated by an AC line;

generating an electric field signal representative of the AC electric field generated by the AC line;

generating a magnetic field signal representative of the AC magnetic field generated by the AC line;

generating a relative load vector signal representative of relative magnitude and phase changes in the magnetic field;

processing the relative load vector change signal to detect and classify loads.

12. The method of claim 11, wherein the processing step comprises determining whether a load has been connected or disconnected from the AC power line.

13. The method of claim 12, wherein the load is a resistive or inductive load.

14. The method of claim 11, wherein the processing step comprises determining whether a load connected to the AC line has been turned on or off.

15. The method of claim 11, wherein the AC line comprises an AC power line having a frequency of 25, 50, 60, or 400 Hertz.

16. The method of claim 11, wherein the processing step comprises processing the relative load vector signal with a threshold detector.

17. The method of claim 11, wherein the processing step comprises processing the relative load vector signal with a slope detector.

18. The method of claim 11, wherein the AC line comprises an AC line buried in ground.

19. The method of claim 11, wherein the placing step comprises placing the AC field sensor near a structure that distorts the electric and magnetic fields generated by the AC line.

20. The method of claim 11, wherein the processing step comprises:

rotating an initial load vector to a common reference point;

rotating a current load vector to the common reference point; and

subtracting the current load vector from the initial load vector.