NON-INTRUSIVE MONITORING OF POWER AND OTHER PARAMETERS

• US 20110109306A1
• Filed: 11/06/2009
• Published: 05/12/2011
• Est. Priority Date: 11/06/2009
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Clifford, Zachary A., Cooley, John J., Avestruz, Al-Thaddeus, Leeb, Steven B.
• Granted Patent: US 8,344,724 B2
• Time in Patent Office: Days
• US Class Current: 324/228
• CPC Class Codes: G01R 31/3277 of low voltage devices, e.g. domestic or industrial devices, such as motor protections, relays, rotation switches
• CPC Class Codes: G01R 33/12 Measuring magnetic properties of articles or specimens of solids or fluids involving magnetic resonance G01R33/20

Abstract

Methods and apparatus for non-intrusive power monitoring and current measurement in a circuit breaker without modification of the breaker panel or the circuit breaker itself. In one example, an inductive pickup sensor senses current from the breaker face, an inductive link transmits power through a steel breaker panel door, and a passive balanced JFET modulator circuit modulates a carrier signal on the inductive link with information regarding the sensed current. A demodulated breaker current signal is available outside of the breaker panel door. The JFET modulator circuit does not require DC power to modulate the carrier signal with the information regarding the sensed current from the breaker. Such methods and apparatus may be interfaced with a spectral envelope load detection system that can monitor multiple loads from a central location.

Claims

1. A system for monitoring a circuit breaker of a circuit breaker unit, the circuit breaker unit comprising a circuit breaker panel and a door, the circuit breaker being positioned at the circuit breaker panel, the circuit breaker comprising a conductor, wherein a current when flowing in the conductor produces a magnetic field in a proximity of the circuit breaker, the system comprising:

a first circuit to produce a carrier signal, the first circuit being positioned outside of the circuit breaker unit;

a first magnetic coupler driven by the carrier signal, the first magnetic coupler being positioned outside of the circuit breaker unit on a first side of the door;

a second magnetic coupler positioned inside of the circuit breaker unit on a second side of the door between the door and the circuit breaker panel, the second magnetic coupler being inductively coupled to the first magnetic coupler, the second magnetic coupler being configured to produce a regenerated carrier signal inside of the circuit breaker unit;

a magnetic field sensor positioned in the proximity of the circuit breaker between the door and the circuit breaker panel, the magnetic field sensor being configured to produce a sensed signal in response to the magnetic field produced by the current when flowing in the conductor; and

a mixer circuit positioned inside of the circuit breaker unit, the mixer circuit being coupled to the second magnetic coupler and the magnetic field sensor, to modulate the regenerated carrier signal in response to the sensed signal.

2. The system of claim 1, wherein the magnetic field sensor is positioned at a face of the circuit breaker.

3. The system of claim 1, wherein the mixer circuit comprises at least one transistor that modulates the regenerated carrier signal in response to the sensed signal.

4. The system of claim 3, wherein the at least one transistor comprises a first transistor having a first gate controlled by the sensed signal and a second transistor having a second gate controlled by the sensed signal.

5. The system of claim 4, wherein the first and second transistors comprise junction field effect transistors.

6. The system of claim 4, wherein the first transistor modulates the regenerated carrier signal during a positive halfwave of the carrier signal and the second transistor modulates the regenerated carrier signal during a negative halfwave of the carrier signal.

7. The system of claim 4, wherein the mixer circuit comprises at least one resistor to bias the sensed signal such that a biased version of the sensed signal is applied to the first and second gates.

8. The system of claim 1, wherein the first magnetic coupler comprises a first coil and a second magnetic coupler comprises a second coil.

9. The system of claim 8, wherein the first magnetic coupler further comprises a magnet.

10. The system of claim 1, wherein the door comprises a ferromagnetic material.

11. The system of claim 10, wherein the ferromagnetic material comprises steel.

12. The system of claim 11, wherein the first magnetic coupler comprises a magnet to at least partially saturate magnetic domains in the steel.

13. The system of claim 1, wherein the first circuit measures a current through the first magnetic coupler to reproduce the sensed signal.

14. The system of claim 1, wherein the first circuit is configured to demodulate a signal received from the first magnetic coupler.

15. The system of claim 1, wherein the mixer circuit is positioned between the circuit breaker panel and the door.

16. A method of sensing an electrical parameter of a circuit breaker, the method comprising:

sensing a field produced by the circuit breaker using a sensor positioned outside of the circuit breaker in a proximity of the circuit breaker.

17. The method of claim 16, further comprising:

positioning the sensor outside the circuit breaker in the proximity of the circuit breaker.

18. The method of claim 17, wherein the circuit breaker is within a circuit breaker unit comprising a door, wherein the sensor is positioned in a region between the circuit breaker and the door.

19. The method of claim 16, wherein the sensor is positioned at a face of the circuit breaker.

20. The method of claim 16, wherein the field is a magnetic field produced by a conductor within the circuit breaker, and wherein the sensor is positioned close enough to the conductor to sense the magnetic field.

21. The method of claim 20, wherein the conductor is a first conductor, and wherein the sensor comprises a second conductor that produces a signal in response to the magnetic field, wherein the second conductor is not wrapped around the first conductor.

22. The method of claim 16, wherein the field is a magnetic field and the sensor comprises one or more coils, the method further comprising:

focusing the magnetic field through the one or more coils.

23. The method of claim 16, wherein the circuit breaker is within a circuit breaker unit, the method further comprising:

producing a sensed signal in response to the field; and

providing the sensed signal to an exterior of the circuit breaker unit.

24. The method of claim 23, wherein the circuit breaker unit comprises a door, and wherein the sensed signal is provided to the exterior of the circuit breaker unit by transmitting a signal through the door.

25. The method of claim 23, further comprising:

transmitting a carrier signal to a region within the circuit breaker unit; and

modulating the carrier signal with the sensed signal to produce a modulated signal.

26. The method of claim 25, further comprising:

transmitting the modulated signal to an exterior of the circuit breaker.

27. The method of claim 26, wherein the modulated signal is transmitted through an inductive link.

28. The method of claim 27, wherein the circuit breaker unit comprises a door, and wherein the modulated signal is transmitted through the door via the inductive link.

29. The method of claim 26, further comprising:

demodulating the modulated signal to determine power monitoring information for the circuit breaker.

30. The method of claim 23, further comprising:

processing the sensed signal to determine information regarding a signal flowing through the circuit breaker.

31. The method of claim 16, wherein the field is a magnetic field and the sensor comprises two or more coils, and the method further comprises:

differentially sensing the magnetic field and rejecting an undesired magnetic field using the two or more coils.

32. A mixer circuit, comprising:

at least one transistor that receives an AC carrier signal and a signal representing a sensed physical parameter, wherein the at least one transistor modulates the AC carrier signal in response to the signal representing the sensed physical parameter.

33. The mixer circuit of claim 32, wherein the at least one transistor comprises a first transistor having a first gate and a second transistor having a second gate, wherein the first and second gates are controlled by the signal representing the sensed physical parameter.

34. The mixer circuit of claim 32, wherein the first and second transistors comprise junction field effect transistors.

35. The mixer circuit of claim 33, wherein the first transistor modulates a current through the mixer circuit during positive halfwaves of the AC carrier signal and the second transistor modulates the current during negative halfwaves of the AC carrier signal.

36. The mixer circuit of claim 33, wherein the mixer circuit comprises at least one resistor to bias the sensed signal such that a biased version of the sensed signal is applied to the first and second gates.