System and method for circuit overcurrent protection

• US 20080165461A1
• Filed: 01/05/2007
• Published: 07/10/2008
• Est. Priority Date: 01/05/2007
• Status: Active Grant

• Current Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Original Assignee: American Power Conversion Corporation (Schneider Electric SE)
• Inventors: Paik, Namwook, Deokar, Vishwas M.
• Granted Patent: US 8,031,455 B2
• Time in Patent Office: Days
• US Class Current: 361/87
• CPC Class Codes: H02H 3/006 Calibration or setting of parameters
• CPC Class Codes: H02H 3/0935 the timing being determined by numerical means
• CPC Class Codes: H03M 1/129 Means for adapting the input signal to the range the converter can handle, e.g. limiting, pre-scaling H03M1/18 takes precedence; Out-of-range indication

Abstract

In one aspect, the invention provides a system for protecting a plurality of circuits including a plurality of circuit protective devices wherein each circuit protective device includes a respective nominal current rating. According to one embodiment, the system includes current sensing circuitry configured to measure a current of each circuit protective device; and a controller configured to receive each of the measured currents. According to one embodiment, the controller is further configured to determine a ratio between a total current being carried by all of the circuit protective devices combined and a total nominal current rating of all of the circuit protective devices combined and employ the ratio to determine a modified nominal current rating of each circuit protective device, respectively. In a further embodiment, the controller is configured to generate an output signal to isolate a selected circuit selected from among the plurality of circuits based on the modified nominal current rating of the circuit protective device included in the selected circuit.

Claims

1. An apparatus comprising:

a current sensor configured to sense a current in a circuit protective device and generate a signal corresponding to the sensed current;

a controller that receives the signal corresponding to the sensed current, the controller configured to estimate an accumulated thermal loading of the circuit protective device based on a thermal characteristic of the circuit protective device and the sensed current; and

an isolation device configured to selectively isolate the circuit protective device,

wherein the controller is further configured to provide an output signal to activate the isolation device and interrupt the current if the accumulated thermal loading exceeds a predetermined maximum thermal loading of the circuit protective device.

2. The apparatus of claim 1, wherein the isolation device is configured to be coupled in series with the circuit protective device.

3. The apparatus of claim 1, further comprising the circuit protection device, and wherein the circuit protective device is a fuse.

4. The apparatus of claim 3, wherein the predetermined maximum thermal loading corresponds to substantially an average melt time of the fuse.

5. The apparatus of claim 4, wherein the predetermined maximum thermal loading of the circuit protective device is less than a thermal loading sufficient to operate the circuit protective device.

6. The apparatus of claim 1 wherein the predetermined maximum thermal loading is determined based on a heating effect of current carried by the circuit protective device.

7. The apparatus of claim 6, wherein the predetermined maximum thermal loading is determined based on a thermal loading determined at a single point on a time-current characteristic curve of the circuit protective device.

8. The apparatus of claim 7, wherein the heating effect of the current is compared with an approximation of a time-current characteristic of the circuit protective device.

9. An overcurrent sensing apparatus comprising:

current sensing circuitry configured to generate an analog output signal representative of a sensed current;

an analog to digital converter configured to receive the analog output signal and generate a digital representation of the analog output signal using a plurality of discrete samples, wherein each of the plurality of discrete samples representative of the analog output signal substantially at or above a maximum current value has a substantially identical magnitude; and

a controller configured to estimate an amount of an overcurrent sensed by the current sensing circuitry by evaluating the samples having the substantially identical magnitude.

10. The apparatus of claim 9, wherein the estimated amount of the overcurrent is determined based on a quantity of consecutive samples having the substantially identical magnitude.

11. The apparatus of claim 9, wherein the estimated amount of the overcurrent is employed to determine when to isolate a circuit protective device in advance of an operation of the circuit protective device responding to the overcurrent.

12. A system for protecting a plurality of circuits including a plurality of circuit protective devices, wherein each circuit protective device includes a respective nominal current rating, the system comprising:

current sensing circuitry configured to measure a current of each circuit protective device; and

a controller configured to receive each of the measured currents, the controller being further configured to determine a ratio between a total current being carried by all of the circuit protective devices combined and a total nominal current rating of all of the circuit protective devices combined and employ the ratio to determine a modified nominal current rating of each circuit protective device, respectively, wherein the controller is further configured to generate an output signal to isolate a selected circuit selected from among the plurality of circuits based on the modified nominal current rating of the circuit protective device included in the selected circuit.

13. The system of claim 12, wherein the controller is configured to apply the ratio to each of the respective nominal current ratings to determine the modified nominal current rating of each of the circuit protective devices.

14. The system of claim 12, wherein the controller is configured to determine each circuit protective device for which the modified nominal current rating is in excess of the nominal current rating of the device, respectively.

15. The system of claim 14, wherein the controller is configured to identify the selected circuit because the selected circuit includes the circuit protective device having a difference between the modified nominal current rating and the nominal current rating of the device that is greatest among the plurality of circuit protective devices.

16. The system of claim 12, wherein the controller is configured to generate the output signal when the ratio is greater than one.

17. The system of claim 12, wherein the circuit protective device protecting the selected circuit operates in response to the output signal.

18. A method for protecting a circuit protection device comprising:

sensing a current in the circuit protective device;

generating a signal corresponding to the sensed current;

estimating an accumulated thermal loading of the circuit protective device based on a thermal characteristic of the circuit protective device and the sensed current; and

interrupting the current if the accumulated thermal loading exceeds a predetermined maximum thermal loading of the circuit protective device.

19. The method of claim 18, wherein the predetermined maximum thermal loading corresponds to substantially an average melt time of the circuit protective device.

20. The method of claim 18, further comprising determining the predetermined maximum thermal loading based on a heating effect of current carried by the circuit protective device.