Circuit breaker and method for estimating temperature of busbar in circuit breaker

Abstract

The present invention is entitled “Circuit breaker and method for estimating the temperature of a busbar in a circuit breaker.” A circuit breaker includes: a busbar; a Rogowski coil disposed around the busbar and configured to sense a current having a first frequency flowing through the busbar; a test injector circuit configured to input a test signal having a second frequency into the Rogowski coil; a high-pass or band-pass filter circuit configured to receive an output of the Rogowski coil, the output including a first component having a first frequency and being proportional to the current flowing through the busbar; and a second component having a second frequency and being proportional to the temperature of the Rogowski coil, and to attenuate the first component of the Rogowski coil output; and an electronic trip unit including a temperature measurement unit configured to receive the output of the high-pass or band-pass filter circuit and estimate the temperature of the busbar based on the output of the high-pass or band-pass filter circuit.

Description

Background Art Technical Field

[0002] The disclosed concepts relate generally to circuit breakers, and more particularly to estimating the temperature of a busbar of a circuit breaker. Background of the Invention

[0004] Circuit breakers (such as, but not limited to, circuit interrupters) are typically used to protect circuits from overcurrent conditions, such as overload conditions, short circuits, or other fault conditions, such as arc faults or ground faults. Circuit interrupters typically include separable contacts. The separable contacts can be manually operated by an operator handle or automatically operated in response to a detected fault condition. Typically, such circuit interrupters include an operating mechanism designed to quickly open and close the separable contacts and a trip mechanism (such as a trip unit) that senses a plurality of fault conditions that automatically trip the circuit interrupter. Upon sensing a fault condition, the trip unit trips the operating mechanism to open the separable contacts.

[0005] Busbar temperature data can be used to diagnose the health of a circuit and assess whether it is operating as expected. For example, if the connections between conductors on a busbar are not tight enough, the added resistance will heat the busbar, causing accelerated wear on interrupter parts.

[0006] While it is useful to have a system in place for measuring the temperature of the busbars for diagnostic purposes, implementing such a system using temperature sensors presents some challenges. The high voltages present on the conductors within the circuit breaker require that the sensors used to measure the temperature of the busbars be electrically isolated. The busbar temperature sensors also need to be able to operate at high temperatures during standard circuit breaker operation. In addition to the electrical and thermal constraints presented by using temperature sensors to measure the temperature of the local busbars, using temperature sensors in circuit interrupters also presents significant design difficulties because the ability to run sensors on the busbars and lead cables back to the electronic trip unit for communication is constrained by the limited internal space in the circuit breaker. There is room for improvement in sensing the temperature of the busbars in circuit breakers. Summary of the Invention

[0007] These needs and other needs are met by embodiments of the presently disclosed concept in which a Rogowski coil is disposed about a busbar of a circuit interrupter to sense current flowing through the busbar, and the resistance of the Rogowski coil is used to determine the temperature of the busbar without the use of a temperature sensor.

[0008] According to one aspect of the presently disclosed concept, a circuit breaker includes: a busbar; a Rogowski coil disposed around the busbar and structured to sense a current having a first frequency flowing through the busbar; a test injector circuit structured to input a test signal having a second frequency into the Rogowski coil; a high-pass or band-pass filter circuit structured to receive an output of the Rogowski coil, the output including a first component having a first frequency and proportional to the current flowing through the busbar, and a second component having a second frequency and proportional to a temperature of the Rogowski coil, and to attenuate the first component of the output of the Rogowski coil; and an electronic trip unit including a temperature measurement unit structured to receive the output of the high-pass or band-pass filter circuit and estimate the temperature of the busbar based on the output of the high-pass or band-pass filter circuit.

[0009] According to another aspect of the presently disclosed concept, a method for estimating the temperature of a busbar in a circuit breaker includes providing a Rogowski coil disposed about the busbar and structured to sense a current having a first frequency flowing through the busbar; injecting a test input signal having a second frequency into the Rogowski coil disposed about the busbar; receiving an output of the Rogowski coil using a high-pass or band-pass filter circuit, the output including a first component having a first frequency and being proportional to the current flowing through the busbar and a second component having a second frequency and being proportional to the temperature of the Rogowski coil; filtering the output of the Rogowski coil using the high-pass or band-pass filter circuit and attenuating the first component of the output of the Rogowski coil; receiving the output of the high-pass or band-pass filter circuit using a temperature measurement unit in an electronic trip unit of the circuit breaker; and estimating the temperature of the busbar based on the output of the high-pass or band-pass filter circuit.

[0010] According to another aspect of the presently disclosed concept, a circuit breaker includes: a busbar; a Rogowski coil disposed around the busbar and structured to sense current flowing through the busbar; a test injector circuit structured to input a test signal to the Rogowski coil; a high-pass or band-pass filter circuit structured to receive an output of the Rogowski coil and high-pass or band-pass filter the output; and an electronic trip unit including: a temperature measurement unit structured to receive the output of the high-pass or band-pass filter circuit and estimate a temperature of the busbar based on the output of the high-pass or band-pass filter circuit; and a current measurement unit structured to receive the output of the Rogowski coil and estimate the current flowing through the busbar based on the output of the Rogowski coil. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A complete understanding of the concepts disclosed herein can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a schematic diagram of a circuit breaker according to an exemplary embodiment of the presently disclosed concept;

[0013] Figure 2 is a more detailed illustration of an exemplary embodiment of the concept disclosed herein Figure 1 Schematic diagram of the circuit breaker;

[0014] Figure 3A is a graph of a waveform of a test signal input to a Rogowski coil disposed around a busbar of a circuit breaker according to an exemplary embodiment of the presently disclosed concept;

[0015] Figure 3B is a graph of a waveform of a signal proportional to the temperature of a Rogowski coil after high-pass or band-pass filtering according to an exemplary embodiment of the presently disclosed concept;

[0016] Figure 4 is a graph of an output signal of a sampling component of a temperature measuring unit of an electronic trip unit of a circuit breaker according to an exemplary embodiment of the presently disclosed concept;

[0017] Figure 5 is a flow chart of a method of estimating the temperature of a busbar in a circuit breaker according to an exemplary embodiment of the presently disclosed concept. DETAILED DESCRIPTION

[0018] Directional phrases used herein, such as, for example, left, right, front, back, top, bottom, and their derivatives, refer to the orientation of elements shown in the drawings and do not limit the claims unless explicitly recited therein.

[0019] Figure 1 is a schematic diagram of a circuit breaker 10 according to an exemplary embodiment of the concepts disclosed herein, and Figure 2 is shown in more detail according to an exemplary embodiment of the concept disclosed herein Figure 1 Schematic diagram of circuit breaker 10. Circuit breaker 10 includes a first terminal 11, a second terminal 12, and a separable contact 16. Circuit breaker 10 also includes a line conductor 14 that connects first terminal 11 and second terminal 12. Line conductor 14 may be formed from one or more busbars. Separable contact 16 is disposed along line conductor 14, and tripping separable contact 16 prevents current from flowing from first terminal 11 through line conductor 14 to second terminal 12. Circuit breaker 10 also includes an operating mechanism 18 that is structured to trip and open separable contact 16.

[0020] The circuit breaker 10 also includes a Rogowski coil 20 that is disposed about the line conductor 14 of the circuit breaker 10 (i.e., the busbar of the line conductor 14) and is structured to sense the current flowing through the line conductor. However, it should be understood that the Rogowski coil can also be used to sense the current flowing through the neutral conductor without departing from the scope of the concepts disclosed herein. The current flowing through the line conductor 14 is expected to have a frequency of approximately 60 Hz, or the standard current frequency provided by the utility. The circuit breaker 10 also includes: a signal conditioner 27 that is electrically connected to the Rogowski coil 20; and a current measurement unit 26 for determining the current flowing through the line conductor 14 based on the output of the signal conditioner 27. The signal conditioner 27 can be analog or digital and can perform amplification and / or integration functions.

[0021] Circuit breaker 10 also includes a test injector circuit 21 electrically connected to Rogowski coil 20. Test injector circuit 21 is structured to input a test signal to Rogowski coil 20 for processing by temperature measurement unit 28 in order to determine the temperature of Rogowski coil 20, which provides an estimate of the temperature of line conductor 14. In some exemplary embodiments, the frequency of the test signal input to Rogowski coil 20 is significantly higher than the frequency of the current flowing through line conductor 14. The higher frequency test signal is attenuated by current measurement components (such as signal conditioner 27 and current measurement unit 26) so that the test signal does not interfere with the measurement of the current flowing through line conductor 14.

[0022] Circuit breaker 10 also includes a high-pass or band-pass filter circuit 22 electrically connected to Rogowski coil 20. High-pass or band-pass filter circuit 22 is structured to receive the output of Rogowski coil 20, which consists of two component signals. The first component signal is proportional to the utility grid current flowing through line conductor 14. The first component is induced in Rogowski coil 20 by the current flowing through line conductor 14. The second component signal is a test signal input to Rogowski coil 20 by test injector circuit 21 and is proportional to the temperature of Rogowski coil 20. For example, as the temperature of Rogowski coil 20 increases or decreases, the resistance of the coils in Rogowski coil 20 changes. This change in resistance causes the magnitude of the test signal to change. High-pass or band-pass filter circuit 22 passes and amplifies the second component (i.e., the test input signal proportional to the temperature of the Rogowski coil) and attenuates the first component (i.e., the signal induced by the utility grid current flowing through line conductor 14).

[0023] For example, Figure 3A A graph showing a waveform 32 of a test signal generated by the test injector circuit 21 and having a frequency of 4800 Hz, which is input to the Rogowski coil 20 of the circuit breaker 10 , is shown. Figure 3B Graph showing the output signal 34 of the 4800 Hz signal output by the high pass or band pass filter circuit 22 after receiving the 4800 Hz output of the Rogowski coil 20. Figure 3B Graph and test signal waveform 32 Figure 3A The difference in amplitude between the graphs indicates that a test input signal having an appropriately selected frequency will be passed by the high pass or band pass filter circuit 22, while the utility grid current signal will be attenuated. While 4800 Hz is an example of a frequency that the test signal and output of the high pass or band pass filter circuit may have, it should be understood that other frequencies may be employed without departing from the scope of the concepts disclosed herein. Figure 3A 1.5 V is used as an example of the amplitude that waveform 32 may have, and Figure 3B 100 mV is used in FIG. 5 as an example of an amplitude that the output signal 34 may have, but it should be understood that other voltage amplitudes may be employed without departing from the scope of the presently disclosed concepts.

[0024] Circuit breaker 10 also includes an electronic trip unit 29, which includes a test injector circuit 21, a high-pass or band-pass filter circuit 22, a temperature measurement unit 28, a signal conditioner 27, and a current measurement unit 26. Current measurement unit 26 receives the output of signal conditioner 27 and is configured to measure the current flowing through line conductor 14 based on the output of signal conditioner 27. Temperature measurement unit 28 receives the output of high-pass or band-pass filter circuit 22 and is configured to estimate the temperature of line conductor 14 based on the output of high-pass or band-pass filter circuit 22. Electronic trip unit 29 is configured to detect a fault in circuit breaker 10 based on the sensed current. In response to detecting the fault, electronic trip unit 29 is configured to trip operating mechanism 18 to open separable contacts 16. Independent of the fault detection function, the temperature of line conductor 14 estimated by temperature measurement unit 28 can be used to detect an overtemperature condition. An overtemperature condition may indicate a loose wiring connection on the busbar. Detection of an overtemperature condition will cause an alarm to sound or generate another type of alarm, indicating that the busbar wiring may need to be inspected.

[0025] The temperature measuring unit 28 includes a sampling component 23 (such as Figure 2 , which is structured to receive the output of high-pass or bandpass filter circuit 22. Sampling component 23 is structured to sample the output of high-pass or bandpass filter circuit 22 at a sampling rate that results in the amplitude of the sampled output signal being substantially the same as the amplitude of the input signal to sampling component 23. Those skilled in the art will appreciate that the sampling rate used by sampling component 23 can be greater than or less than the Nyquist rate. If a sampling rate less than the Nyquist rate is used, the sampled output signal will be an alias of the original test signal. In some exemplary embodiments, using a sampling rate less than the Nyquist rate can utilize fewer processing resources in electronic trip unit 29. The sampling rate can be selected to coincide with the rate at which the electronic trip unit already reads the current and can result in aliasing of the output of high-pass or bandpass filter circuit 22. Those skilled in the art will appreciate that undersampling at an appropriately selected rate will result in the sampled output signal retaining RMS amplitude information about the input signal to sampling component 23.

[0026] For example, in Figure 3B In the 4800Hz test injection signal ( Figure 2 After the 4800 Hz output signal 34 is input to the Rogowski coil 20 and the output of the Rogowski coil 20 is input to the high-pass or band-pass filter circuit 22, the high-pass or band-pass filter circuit 22 outputs the 4800 Hz output signal 34. Figure 4 In the example, the 4800 Hz high-pass or band-pass filter output signal 34 is input to the sampling component 23, which undersamples the output signal 34 at a rate of 4000 Hz (e.g., Figure 2 ). This results in an 800 Hz sampling component output signal 52 having an amplitude proportional to the test injection signal input wave. While 4000 Hz is an example of a frequency at which the sampling component may sample and an example of a rate at which the electronic trip unit may read the current, it should be understood that other frequencies may be employed by the sampling component without departing from the scope of the presently disclosed concepts. While sampling the 4800 Hz high-pass filter output signal at a rate of 4000 Hz produces an exemplary 800 Hz sampling component output signal, it should be understood that sampling component output signals of other frequencies may be produced without departing from the scope of the presently disclosed concepts, as the frequency of the sampling component output signal depends on both the frequency of the high-pass or bandpass filter output signal and the sampling rate employed by the sampling component.

[0027] Temperature measurement unit 28 also includes a frequency multiplier or mixer component 24 configured to receive the output of sampling component 23. Frequency multiplier or mixer component 24 is configured to multiply the output of sampling component 23 by sine and cosine signals having the same frequency as the sampling component output signal, or to mix the output of sampling component 23, in order to eliminate any unwanted signals at other frequencies that may be components of the sampling component output signal, such as harmonics of the utility current signal. Those skilled in the art will appreciate that the unwanted signal and its harmonics can be removed by selecting an appropriate averaging time. For example, by averaging the output of sampling component 23 over an integer multiple of the device period and its harmonics, the net resulting signal at the unwanted utility frequency and its harmonics will be zero.

[0028] The temperature measurement unit 28 also includes a frequency averaging function component 25 that is structured to remove all components except the DC component from the output signal of the frequency multiplier or mixer component 24. The temperature measurement unit 28 also includes a processor that calculates the resistance of the Rogowski coil 20 based on the output of the frequency averaging function component 25 using the current through the Rogowski coil 20, the ambient temperature, and the temperature coefficient of the winding of the Rogowski coil 20. As the resistance of the winding of the Rogowski coil 20 changes with temperature, the resistance indicates the temperature of the winding of the Rogowski coil 20, which in turn is an estimate of the temperature of the line conductor 14. In an exemplary embodiment, the temperature measurement unit 28 may output an alarm when the estimated temperature (based on the resistance of the winding of the Rogowski coil 20) reaches or exceeds a predetermined threshold level.

[0029] Figure 5 is a flowchart of a method of estimating a temperature of a bus bar according to an exemplary embodiment of the presently disclosed concept. Figure 5 The method can be used, for example, Figure 1 and Figure 2 The circuit breaker 10 shown, and combined with Figure 1 and Figure 2 The present invention will be described with reference to a circuit breaker 10 shown. However, it will be appreciated that the method may be used in other devices without departing from the scope of the disclosed concepts.

[0030] The method begins at 100, where a Rogowski coil 20 is provided and disposed around a line conductor 14 of a circuit breaker 10. At 102, a test input signal is injected into the Rogowski coil 20. At 104, a high-pass or band-pass filter circuit 22 receives the output of the Rogowski coil 20. At 106, the output of the Rogowski coil 20 is filtered using the high-pass or band-pass filter circuit 22. At 108, a temperature measurement unit 28 receives the output of the high-pass or band-pass filter circuit 22. At 110, the temperature of the line conductor 14 is estimated using the temperature measurement unit 28.

[0031] While specific embodiments of the concepts disclosed herein have been described in detail, it will be appreciated by those skilled in the art that various modifications and substitutions of those details may be developed in light of the overall teachings of this disclosure. Accordingly, the specific arrangements disclosed are intended to be illustrative only and not limiting of the scope of the concepts disclosed herein, which is to be given the full scope of the appended claims and any and all equivalents thereof.

Claims

1. A circuit breaker, comprising: busbar; a Rogowski coil disposed about the busbar and structured to sense a current having a first frequency flowing through the busbar; a test injector circuit structured to input a test signal having a second frequency into the Rogowski coil; a high-pass or band-pass filter circuit structured to receive an output of the Rogowski coil, the output comprising a first component having the first frequency and being proportional to the current flowing through the bus, and a second component having the second frequency and being proportional to the temperature of the Rogowski coil, and to attenuate the first component of the output of the Rogowski coil; and An electronic trip unit includes a temperature measurement unit structured to receive an output of the high-pass or band-pass filter circuit and estimate a temperature of the busbar based on the output of the high-pass or band-pass filter circuit.

2. The circuit breaker of claim 1, wherein the second frequency is significantly higher than the first frequency.

3. The circuit breaker of claim 1, wherein the second frequency is at least three times the first frequency.

4. The circuit breaker of claim 2, wherein the electronic trip unit includes a current measurement circuit structured to receive the output of the Rogowski coil and to attenuate the second component having the second frequency.

5. The circuit breaker of claim 1 , wherein the temperature measurement unit comprises a sampling component structured to sample the output of the high-pass or band-pass filter circuit at a third frequency, wherein the output of the sampling component has a fourth frequency, wherein the temperature measurement unit comprises a frequency multiplier or mixer component, wherein the frequency multiplier or mixer component is structured to multiply the output of the sampling component by the sine and cosine of the fourth frequency or to mix the output of the sampling component by the sine and cosine of the fourth frequency, wherein the temperature measurement unit comprises a frequency averaging function component structured to remove all components except a DC component from the output of the frequency multiplier or mixer component, and The temperature measurement unit includes a temperature calculation component configured to calculate the temperature of the Rogowski coil.

6. The circuit breaker of claim 5, wherein the output of the sampling component is a signal having an amplitude proportional to the amplitude of the output of the high-pass or band-pass filter circuit.

7. The circuit breaker of claim 5, wherein the fourth frequency is an aliased frequency of the test signal.

8. The circuit breaker of claim 1 , further comprising: First terminal; Second terminal; a separable contact movable between a closed position and an open position, the first terminal and the second terminal being electrically disconnected from each other when the separable contact is in the open position; an operating mechanism structured to open the separable contacts; and An actuator is structured to cooperate with the operating mechanism to trip open the separable contacts.

9. A method for estimating the temperature of a busbar in a circuit breaker, the method comprising: providing a Rogowski coil disposed about the busbar and structured to sense a current having a first frequency flowing through the busbar; injecting a test signal having a second frequency into the Rogowski coil disposed around the busbar; receiving an output of the Rogowski coil using a high-pass or band-pass filter circuit, the output comprising a first component and a second component, the first component having the first frequency and being proportional to the current flowing through the bus, the second component having the second frequency and being proportional to the temperature of the Rogowski coil; filtering the output of the Rogowski coil and attenuating the first component of the output of the Rogowski coil using the high-pass or band-pass filter circuit; receiving the output of the high-pass or band-pass filter circuit using a temperature measurement unit in an electronic trip unit of the circuit breaker; as well as The temperature of the bus is estimated based on the output of the high pass or band pass filter circuit.

10. The method of claim 9, wherein the second frequency is significantly higher than the first frequency. The method of claim 9 , wherein the second frequency is at least three times the first frequency.

12. The method of claim 9, wherein the electronic trip unit comprises a current measurement circuit structured to receive the output of the Rogowski coil and to attenuate the second component having the second frequency.

13. The method of claim 9, wherein the temperature measurement unit comprises a sampling component structured to sample the output of the high-pass or band-pass filter circuit at a third frequency, wherein the output of the sampling component has a fourth frequency, wherein the temperature measurement unit comprises a frequency multiplier or mixer component, wherein the frequency multiplier or mixer component is structured to multiply the output of the sampling component by the sine and cosine of the fourth frequency or to mix the output of the sampling component by the sine and cosine of the fourth frequency, wherein the temperature measurement unit comprises a frequency averaging function component structured to remove all components except a DC component from the output of the frequency multiplier or mixer component, and The temperature measurement unit includes a temperature calculation component configured to calculate the temperature of the Rogowski coil.

14. The method of claim 13, wherein the output of the sampling component is a signal having an amplitude proportional to the amplitude of the output of the high-pass or band-pass filter circuit. The method of claim 13 , wherein the fourth frequency is an aliased frequency of the test signal.

16. The method of claim 9, wherein the circuit breaker comprises: First terminal; Second terminal; a separable contact movable between a closed position and an open position, the first terminal and the second terminal being electrically disconnected from each other when the separable contact is in the open position; an operating mechanism structured to open the separable contacts; and An actuator is structured to cooperate with the operating mechanism to trip open the separable contacts.

17. A circuit breaker, comprising: busbar; a Rogowski coil disposed about the bus bar and structured to sense current flowing through the bus bar; a test injector circuit structured to input a test signal into the Rogowski coil; a high-pass or band-pass filter circuit structured to receive the output of the Rogowski coil and perform high-pass or band-pass filtering on the output of the Rogowski coil; and an electronic trip unit comprising: a temperature measurement unit structured to receive an output of the high-pass or band-pass filter circuit and estimate the temperature of the busbar based on the output of the high-pass or band-pass filter circuit; and a current measuring unit structured to receive an output of the Rogowski coil and estimate the current flowing through the bus based on the output of the Rogowski coil.

18. The circuit breaker of claim 17, wherein the temperature measurement unit comprises a sampling component structured to sample the output of the high-pass or band-pass filter circuit, wherein the temperature measurement unit comprises a frequency multiplier or mixer component, wherein the frequency multiplier or mixer component is structured to perform frequency multiplication or mixing on the output of the sampling component, wherein the temperature measurement unit comprises a frequency averaging function component structured to remove all components except a DC component from the output of the frequency multiplier or mixer component, and The temperature measurement unit includes a temperature calculation component configured to calculate the temperature of the Rogowski coil.

19. The circuit breaker of claim 18, wherein the output of the sampling component is a signal having an amplitude proportional to the amplitude of the output of the high-pass or band-pass filter circuit.

20. The circuit breaker of claim 17, further comprising: First terminal; Second terminal; a separable contact movable between a closed position and an open position, the first terminal and the second terminal being electrically disconnected from each other when the separable contact is in the open position; an operating mechanism structured to open the separable contacts; and An actuator is structured to cooperate with the operating mechanism to trip open the separable contacts.

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