Thermal memory in a fault powered system

• US 8,665,574 B2
• Filed: 11/12/2010
• Issued: 03/04/2014
• Est. Priority Date: 11/12/2010
• Status: Active Grant

• Current Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Original Assignee: Schneider Electric USA, Inc. (Schneider Electric SE)
• Inventors: Studer, Richard Allen II, Moffitt, Ryan James, Meehleder, Steve M.
• Primary Examiner(s): BAUER, SCOTT ALLEN
• Application Number:
  US12/945,616
• Publication Number:
  US 20120123762A1
• Time in Patent Office: 1,208 Days
• Field of Search: 361/93.6
• US Class Current: 361/93.6
• CPC Class Codes: H02H 1/06 Arrangements for supplying operative power power supply arrangements in general G05F, H02M
• CPC Class Codes: H02H 3/085 making use of a thermal sensor, e.g. thermistor, heated by the excess current also responsive to the temperature of the protected device H02H5/041, thermal images H02H6/00
• CPC Class Codes: H02H 6/005 using digital thermal images
• CPC Class Codes: H02H 7/226 for wires or cables, e.g. heating wires

Abstract

A circuit breaker system for providing thermal protection to a conductor conducting current from a power source to a load. While the power source is connected to the load, a microcontroller is powered by the current passing through the conductor to thermally model the temperature of the conductor. If the microcontroller determines that the temperature of the conductor has risen to an undesirable or unsafe level, the circuit breaker disconnects the power source from the load and the current no longer passes through the conductor. With no current passing through the conductor, the microcontroller no longer receives power from the conductor. Instead, the microcontroller continues to model the temperature of the conductor as the conductor cools to an ambient temperature by receiving power from an energy storage device. Accordingly, the microcontroller continuously models the temperature of the conductor until the temperature of the conductor cools to the ambient temperature.

Claims

1. A circuit breaker for protecting a load, comprising

a temperature sensor that measures an ambient temperature of the circuit breaker;

a primary conductor for conducting a primary current from a power source, through the circuit breaker, to a load being protected by the circuit breaker;

a current transformer coupled to the primary conductor;

a secondary conductor coupled to the current transformer such that a secondary current is induced in the secondary conductor in response to the primary current flowing in the primary conductor;

an energy storage device that stores energy related to the secondary current in response to the primary current passing through the primary conductor;

a trip module that includes a controller programmed to continuously process a thermal model of the primary conductor while the primary current is passing through the primary conductor and, if the primary current is not passing through the primary conductor, until the thermal model indicates that the temperature of the primary conductor converges to about the ambient temperature measured by the temperature sensor as the controller is being powered by the energy stored in the energy storage device.

2. The circuit breaker of claim 1, wherein the energy storage device is a high-capacity capacitor.

3. The circuit breaker of claim 2, wherein the high-capacity capacitor is in the trip module.

4. The circuit breaker of claim 1 further comprising the trip module further including an analog to digital converter coupled to the secondary conductor, the analog to digital converter being configured to provide a digital signal indicative of the secondary current to the controller.

5. The circuit breaker of claim 4, wherein the analog to digital converter is in further electrical communication with a temperature sensor configured to provide an indication of the ambient temperature of the circuit breaker, the analog to digital converter being further configured to provide a signal that is indicative of the ambient temperature to the controller, the controller being programmed to process the thermal model based on the indication of the ambient temperature.

6. The circuit breaker of claim 4, wherein the thermal model includes a function that includes root-mean-squared (RMS) values of the secondary current and physical and geometric characteristics of the primary conductor.

7. The circuit breaker of claim 6, wherein the function is

Θ

_k+1=Θ

_k+α

└

A·

I_K²−

Θ

_k┘

,

where Θ

_k+1 represents the accumulated heat of the system after k+1 samples, Θ

_k represents the accumulated heat of the system after k samples, A is a constant depending on the resistance, mass and specific heat of the primary conductor, I_K is the digital signal indicative of the secondary current from the analog to digital converter, α

is a constant depending on the physical and geometrical characteristics of the primary conductor, and k represents an integer number indicating a sample number.

8. The circuit breaker of claim 1, wherein the thermal model produces an estimation of accumulated heat, y, of the primary conductor according to a function represented by:

9. The circuit breaker of claim 1, wherein the trip module is coupled to a tripping mechanism, the trip module being programmed to detect a thermal fault and communicate a trip signal to the tripping mechanism, the tripping mechanism being configured to disconnect the power source from the load at least in response to receiving the signal from the trip module.

10. The circuit breaker of claim 1, wherein the trip module is configured to direct operating power from the secondary conductor to the controller if the primary current is passing through the primary conductor and to direct operating power from the energy storage device to the controller if the primary current is not passing through the primary conductor.

11. The circuit breaker of claim 1, wherein the thermal model models a cooling of the primary conductor responsive to the tripping mechanism disconnecting the power source from the load.

12. The circuit breaker of claim 1, further comprising an output device for displaying an indication of the temperature of the primary conductor based on the thermal model.

13. The circuit breaker of claim 1, wherein the thermal model is based on the secondary current.

14. A method for modeling thermal characteristics of a primary conductor coupled to a circuit breaker protecting a load, comprising:

powering a controller with a first power source derived from a primary current passing through the primary conductor in the circuit breaker;

inducing, via a current transformer coupled to the primary conductor, a secondary current in a secondary conductor responsive to the primary current passing through the primary conductor;

storing, in a second power source, energy derived from the secondary current induced via the current transformer;

measuring an indication of the primary current passing through the primary conductor;

determining a thermal model of the temperature of the primary conductor using the controller and based at least in part on the measured indication of the primary current while the controller is being powered by the first power source, the thermal model generating an output value indicative of the temperature of the primary conductor;

comparing the output value with a trip value;

generating a trip signal based on the comparing to cause the circuit breaker to disconnect the primary conductor from the load;

responsive to generating the trip signal, powering the controller with the second power source while the primary conductor remains disconnected from the load;

measuring an ambient temperature of the circuit breaker; and

determining the thermal model of the temperature of the primary conductor while the controller is being powered by the second power source until the thermal model indicates that the temperature of the primary conductor converges to the ambient temperature measured by the temperature sensor.

15. The method of claim 14, wherein the first power source includes the secondary conductor electrically coupled to the primary conductor by the current transformer.

16. The method of claim 15, wherein the second power source includes a capacitor.

17. The method of claim 16, further comprising charging the capacitor while the controller is powered by the first power source.

18. The method of claim 14, further comprising displaying a representation of the output of the thermal model on an output device of the circuit breaker.

19. The method of claim 14, further comprising receiving the trip value via an input device of the circuit breaker.

20. The method of claim 14, wherein the thermal model includes a function that includes root-mean-squared (RMS) values of the secondary current and physical and geometric characteristics of the primary conductor, the function being represented by:

Θ

_k+1=Θ

_k+α

└

A·

I_K²−

Θ

_k┘

,

where Θ

_k+1 represents the accumulated heat of the system after k+1 samples, Θ

_k represents the accumulated heat of the system after k samples, A is a constant depending on the resistance, mass and specific heat of the primary conductor, I_K is the digital signal indicative of the secondary current from the analog to digital converter, α

is a constant depending on the physical and geometrical characteristics of the primary conductor, and k represents an integer number indicating a sample number.

21. The method of claim 14, wherein the thermal model produces an estimation of accumulated heat, y, of the primary conductor according to a function represented by: