CLIAMS:1. A method for providing selectivity between circuit breakers configured in series to have an upstream circuit breaker and one or more downstream circuit breakers, wherein the selectivity feature is incorporated in the upstream circuit breaker, and wherein the one or more downstream circuit breakers are conventional circuit breakers, wherein the method comprises the steps of:
sensing, at set regular intervals, successive samples of an analog current signal associated with the upstream circuit breaker;
detecting, at the upstream circuit breaker, peak current value of the sensed analog current signal;
identifying, at the upstream circuit breaker, a first condition corresponding to the detected peak current being greater than a pre-determined first threshold value for a first pre-determined number of consecutive samples of the analog current signal;
identifying, at the upstream circuit breaker, a second condition corresponding to the detected peak current being greater than a pre-determined second threshold value for a second pre-determined number of samples of the analog current signal, wherein the second pre-determined number is greater than the first pre-determined number; and
sending a trip command to trip the upstream circuit breaker when both the first condition and the second condition are met.

2. The method of claim 1, wherein the upstream circuit breaker incorporates a microcontroller.

3. The method of claim 2, wherein the successive samples of the analog current signal are received at an ADC channel of the microcontroller.

4. The method of claim 1, wherein the step of sending a trip command is preceded by a step of determining health condition of trip circuit associated with the upstream circuit breaker.

5. The method of claim 4, wherein the step of determining health condition of the trip circuit comprises detecting voltage of tripping solenoid associated with the upstream circuit breaker.
6. The method of claim 1, wherein the upstream circuit breaker is either a Moulded Case Circuit Breaker (MCCBs) or an Air Circuit Breaker (ACBs).
7. The system of claim 1, wherein the current sensor is built-in feature of the upstream circuit breaker.

8. A system for providing selectivity between circuit breakers configured in series to have an upstream circuit breaker and one or more downstream circuit breakers, wherein the system is incorporated in the upstream circuit breaker, and wherein the one or more downstream circuit breakers are conventional circuit breakers, wherein the system comprises:
a current sensor incorporated in the circuit breaker and configured to sense successive samples of an analog current signal at set regular interval;
a microcontroller configured to receive the sensed successive samples of the analog current signal and further configured to identifying a first condition corresponding to the detected peak current being greater than a pre-determined first threshold value for a first pre-determined number of consecutive samples of the analog current signal sensed at the set regular interval; and wherein the microcontroller is further configured to identify a second condition corresponding to the detected peak current being greater than a pre-determined second threshold value for a second pre-determined number of samples of the analog current signal, wherein the second pre-determined number is greater than the first pre-determined number, and wherein the microcontroller is further configured to send a trip command to trip the circuit breaker when both the first condition and the second condition are met.

9. The system of claim 8, wherein the successive samples of the analog current signal are received at the ADC channel of the microcontroller.

10. The system of claim 1, before sending a trip command, health condition of trip circuit associated with the upstream circuit breaker is determined by detecting voltage of tripping solenoid associated with the upstream circuit breaker.
,TagSPECI:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of low voltage power equipment. In particular, it relates to systems and methods for selectivity between circuit breakers connected in series, in response to an overcurrent condition.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art
[0003] A fundamental requirement in any electrical system is proper overcurrent protection of conductors and equipment. Overcurrent is a condition when current flowing through a system exceeds rated current of the equipment or conductors. Such a condition may result from an overload, short circuit, or ground fault. An overcurrent protection device protects the system by interrupting current flow through the part of the circuit where fault has occurred. Such interruption is required to be performed before the current reaches a value that may cause danger to the system and personnel alike. Interruption of the part of the circuit where fault has occurred also improves up-time of the system by ensuring that healthy part of the system continues to operate.
[0004] A typical power distribution system can have several levels of distribution and accordingly involve circuit protection devices at every level. In the event of an overcurrent fault, to minimize the extent and duration of downtime, it is imperative that the protection devices such as circuit breakers interrupt the fault current in a timely manner. For instance, if there is a fault in a downstream circuit, circuit breaker in the feeder nearest the fault will attempt to interrupt the affected circuit. This would ensure that upstream circuits and other healthy feeders in the downstream circuit continue to supply load. If the circuit breaker in the feeder nearest the fault fails to interrupt the affected circuit, the upstream circuit will be forced into an overload condition and the associated upstream circuit breaker trips after a pre-determined time delay and the entire system would be forced to shut down to prevent damage.
[0005] Co-ordination between settings of circuit breakers of a system is a critical aspect that can ensure continued operation of healthy parts of the system in the event of fault in another part. It will be however appreciated that even a small modification, intentional or otherwise, during monitoring or maintenance of the system is liable to break the optimized selectivity logic. Again, in very large electrical systems that include large number of feeder circuits at different distribution levels, it is a big challenge to effectively co-ordinate current and time settings to enable proper co-ordination and thereby selectivity between the circuit breakers at different levels which often leads to multiple tripping and outage of healthy parts of the system. Upstream and downstream circuit breakers tend to sense the fault and give trip command as per their settings, which in a large electrical system may be very close and thus lead to multiple undesirable tripping. In such situations, it becomes critical to have hard wired communication between the upstream and downstream circuit breakers to ensure that the upstream breaker only trips if the downstream breaker has not been able to clear the fault. For instance, the contacts of the downstream breaker are hard wired upstream to provide status of the downstream breaker to the upstream breaker and prevent false tripping.
[0006] There is therefore a need for a system and method for selectivity between circuit breakers connected in series, in response to an overcurrent condition, that at least overcomes some of the aforementioned drawbacks of the prior art.
[0007] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0008] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0009] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0010] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0011] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0012] An object of the present disclosure is to mitigate short comings of conventional systems and methods for selective tripping of circuit breakers (interchangeably referred to as selectivity between circuit breakers) connected in series in response to an overcurrent condition.
[0013] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers that is simple.
[0014] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers that is cost effective.
[0015] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers that is easily customizable from a single location.
[0016] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers that is reliable.
[0017] Another object of the present disclosure is to provide a scalable system and method for selectivity between circuit breakers.
[0018] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers such that there is no need for hard wired communication or signal transmission between the series connected circuit breakers.
[0019] Another object of the present disclosure is to provide a system and method for selectivity between circuit breakers that obviates need for signal interconnection between current measuring devices of the series connected circuit breakers.

SUMMARY
[0020] Aspects of present disclosure relate to systems and methods for selective tripping of circuit breakers (interchangeably referred to as selectivity between circuit breakers) that are connected in series and configured to trip in response to an overcurrent condition. In an embodiment the disclosed system and method uses time-current selectivity technique to achieve over current selectivity between the circuit breakers placed in series. Time-current selectivity makes circuit breakers to trip by adjusting the short circuit protections trip time so that the load-side circuit breaker (downstream circuit breaker) trips more rapidly than the supply-side circuit breaker (upstream circuit breaker).
[0021] In an embodiment, if the downstream circuit breaker fails to clear the fault with in specified time limit, the upstream circuit breakers can clear the fault. In an aspect, if fault happens between the downstream circuit breaker and the upstream circuit breaker, the upstream circuit breaker can clear the fault with in a specified time limit.
[0022] In an embodiment, the disclosed selectivity feature can be incorporated in the upstream circuit breaker and the downstream circuit breaker can be a standard protection device. The upstream circuit breaker can identify the fault zone and can accordingly issue a trip command. In an aspect, there is no dialogue between the current sensing and measuring devices of the upstream circuit breaker & the downstream circuit breaker. The downstream circuit breaker can be any protection device that can be without electronic trip unit.
[0023] In an aspect, the disclosure provides a system for selectivity between circuit breakers connected in series that can include at least one current sensor operatively coupled with the upstream circuit breaker and configured to sense successive samples of associated analog current signals at regular intervals. In an embodiment, the current sensor can be a built-in feature of the circuit breaker.
[0024] System of the present disclosure can further include a current parameter detector that can be configured to detect peak current of the sensed analog current signals. In an embodiment a plurality of such detected peak current in sensed samples can prevent false detection of overcurrent conditions.
[0025] The system can further incorporate a conditioning unit that can be configured to condition the sensed analog current signals. Again a plurality of successive samples can be checked to ensure consistency of values associated with the conditioned sensed analog current signals.
[0026] The system can further include a microcontroller that can be configured to receive digital signals corresponding to the detected peak current and the conditioned analog current signals. The digital signals can be either generated by an Analog-to Digital Converter (ADC) or by the ADC channels of the microcontroller. In accordance with an embodiment, the microcontroller can then check for a first condition wherein the detected peak current sensed consistently over a pre-determined number (say N numbers) of sensed successive signals are greater than a pre-determined threshold value. In an aspect the time period corresponding to N numbers of successive signals can be the time limit within which the downstream circuit breaker should clear the fault. The microcontroller also checks for a second condition wherein the conditioned analog current is greater than the pre-determined threshold value for N+1 numbers of successive signals. If both these conditions are satisfied, an overload condition is considered to have occurred and a trip command is sent by the microcontroller to the circuit breaker.
[0027] In an embodiment, the system can further include a trip circuit health monitor that can be configured to determine and send status related to the health of the trip circuit of the circuit breaker before the microcontroller sends a trip command. In an embodiment, the trip circuit health monitor can be configured to determine the health of the trip circuit by sensing the voltage of tripping solenoid associated with the circuit breaker.
[0028] In another aspect, the disclosure provides a method for selectivity between circuit breakers connected in series in response to an overcurrent condition wherein the method can include sensing successive samples of analog current signals associated with each circuit breaker at regular intervals; detecting peak current of the sensed analog current signals; conditioning the sensed analog current signals; receiving digital signals corresponding to the detected peak current and the conditioned analog current signals, by a microcontroller; identifying a first condition corresponding to the detected peak current being greater than a pre-determined first threshold value for a pre-determined number of samples of the analog current signals; identifying a second condition corresponding to the conditioned analog current being greater than a pre-determined second threshold value for a pre-determined number of samples of the analog current signals; and sending a trip command to at least one circuit breaker associated with a circuit satisfying the first condition and the second condition.
[0029] In an embodiment, the step of sending a trip command can be preceded by a step of determining healthy condition of trip circuit associated with the circuit breaker.
[0030] In an embodiment, the step of determining healthy condition of trip circuit can include detecting voltage of tripping solenoid associated with the circuit breaker.
[0031] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components

BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0033] FIG. 1 illustrates a typical arrangement of circuit breakers in a power distribution circuit indicating possibilities of fault occurrences.
[0034] FIG. 2 illustrates an exemplary flow diagram of a method for selectivity between circuit breakers connected in series in response to an overcurrent condition in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0035] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0036] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0037] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0038] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0039] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0040] Embodiments of the present disclosure relate to systems and methods for selectivity between circuit breakers connected in series in response to an overcurrent condition. Coordination or selectivity is directed to localization of an overcurrent condition to restrict outages to the circuit or equipment affected and this is accomplished by the choice of overcurrent protective devices and their ratings or settings. The system and method of the present disclosure are based on time-current selectivity that makes the circuit breaker trip by adjusting the short circuit protection trip time so that the load-side or downstream circuit breaker trips more rapidly than the supply-side or upstream circuit breaker. In the event that the downstream circuit breaker fails to clear the fault within a pre-determined time limit, the upstream circuit breaker clears the faults. Again if fault occurs on an upstream feeder, the upstream circuit breaker can clear the fault within pre-determined time limit.
[0041] Referring to FIG. 1 wherein a typical arrangement of circuit breakers in a power distribution circuit is illustrated. As shown, when protection devices are connected in series and a short circuit fault happens at say level 1 near a downstream circuit breaker, both upstream and downstream circuit breaker will sense the fault and give trip command as per their settings and there shall be no discrimination between protection devices connected in series. To achieve the selectivity, hard wired communication is typically provided between downstream circuit breaker and upstream circuit breakers.
[0042] In an embodiment the disclosed system and method uses time-current selectivity technique to achieve over current selectivity between the circuit breakers placed in series. Time-current selectivity makes circuit breakers to trip by adjusting the short circuit protections trip time so that the load-side circuit breaker (downstream circuit breaker) trips more rapidly than the supply-side circuit breaker (upstream circuit breaker).
[0043] In an embodiment, if the downstream circuit breaker fails to clear the fault with in specified time limit, the upstream circuit breakers can clear the fault. In an aspect, if fault happens between the downstream circuit breaker and the upstream circuit breaker, the upstream circuit breaker can clear the fault with in a specified time limit.
[0044] In an embodiment, the disclosed selectivity feature can be incorporated in the upstream circuit breaker and the downstream circuit breaker can be a standard protection device. The upstream circuit breaker can be configured to identify the fault zone and can accordingly issue a trip command. In an aspect, there is no dialogue through means such as but not limited to hardwired connection between the current measuring devices of the upstream circuit breaker & the downstream circuit breaker. The downstream circuit breaker can be any protection device that can be without electronic trip unit.
[0045] In an embodiment, the disclosed circuit breaker that incorporates discrimination feature with downstream device can consist of means to sense short circuit fault. The short circuit fault current can for example be a current above 12 times the nominal current of the circuit breaker (12In). To achieve functionality of discrimination and for faster sensing of fault, analog sensing circuit can be used which measures the current peak and holds on the fault threshold for a while such as for 5ms.
[0046] In an embodiment, the disclosed circuit breaker can further consist of a microcontroller with an ADC circuit. The ADC channel of the microcontroller can receive the sensed peak current value. To eliminate any possibility of false sensing of noise, several successive samples of the peak value can be sensed at set time intervals.
[0047] In an embodiment, the microcontroller can incorporate logic to successfully detect short circuit fault with discriminating feature. The microcontroller can look for two conditions (referred to as cases hereinafter) that need to be satisfied for concluding that the short circuit fault has occurred that a downstream circuit breaker has failed to act on or the fault has occurred between the upstream circuit breaker and the downstream circuit breaker. The first case can be the measured analogue current exceeding a set threshold value for a set number of successive samples measured at set interval. If the sensed sample value crosses the set threshold value for set number of successive measurements, then the first case can be considered as satisfied. In an aspect the set number of successive samples measured at set interval can correspond to the time period within which the downstream circuit breaker is set to trip on detection of short circuit current.
[0048] In an embodiment, after the first case is satisfied, the microcontroller logic can continue to check for second case, where it can sense R, Y and B phase signal conditioning output using ADC channel of the microcontroller. Again, multiple successive samples of the phases can be sensed at set regular interval. If the sample values cross a second threshold value then second case gets satisfied.
[0049] In an embodiment, if both the cases are satisfied, then controller can check for health of tripping solenoid, i.e. Flux Shift Device (FSD) of the circuit breaker. If the controller detects the healthy condition of voltage, FSD triggering signal can be given by microcontroller digital output pin. In case the second case is not satisfied then the logic will again restart and can check for both conditions again.
[0050] In an embodiment, the present disclosure provides a method for working of selectivity feature in a circuit breaker with a downstream circuit breaker, in response to an overcurrent condition. FIG. 2 illustrates an exemplary flow diagram 200 of the disclosed method wherein at step 202, current sensing activity can be started. The sensing activity can include sensing successive samples of analog current signals associated with the circuit breaker at regular intervals. This eliminates any possibility of false sensing of noise and ensures that false tripping is prevented. To achieve functionality of discrimination and for faster sensing of fault, analog sensing circuit can be used which measures the current peak and holds on the fault threshold for a while such as for 5ms. This overcomes the time taken by microcontroller to wake up after power on. If fault occurs at make on condition then threshold peak will be sensed but will not be conditioned till the time micro-controller wakes up. Hence the peak is sensed and held by circuit for some time such as 5ms for microcontroller processing.
[0051] At step 204 of the disclosed method it can be checked if fault is detected or not. If fault is detected the method can go to step 238 (to be described in later paragraphs).In an embodiment, the disclosed method can follow a logic that requires two conditions (referred to as cases – case 1 and case 2 - hereinafter) to be satisfied for concluding that the short circuit fault has occurred that a downstream circuit breaker has failed to act on or the fault has occurred between the upstream circuit breaker and the downstream circuit breaker.
[0052] At step 204, if it is found that the two cases are not satisfied, the method can continue to check if the two cases are satisfied. At step 206, it can check if case-1 is satisfied. If it is satisfied the method can go to step 218 to check case-2 (to be described in later paragraphs). In case case-1 is not satisfied the method can go to steps 208 and 210 wherein signal of the analogue current can be checked to see if it exceeds the set threshold value. The set threshold can for example be a current above 12 times the nominal current of the circuit breaker (12In). In case no current above the threshold is detected, the detection can be continued for further detection cycles.
[0053] On the other hand if the detected current is above the set threshold, the successive samples of analog current signals associated with the circuit breaker can be sensed at regular intervals and checked if the current is above the set threshold value for a set number (say N numbers) of consecutive samples.and N consecutive measurement can correspond to the time within which the downstream circuit breaker should have tripped to isolate the feeder circuit that experienced the short circuit current. In the exemplary flow diagram N is taken as 2 and steps 212 and 214 can confirm that analogue current signal is above the set threshold value for a set number of consecutive samples. If the requirement is not met, the method can continue to see if the case 1 is satisfied. If case1 is met, at step 216 the method can be directed to look for case 2 and directed to at step 218.
[0054] In an embodiment, if the first case is met, the logic can look for second case wherein at step 218 and 220 after setting the execution counter, the consecutive current samples of analogue current are measured and checked if it is above the set second threshold value.. At step 222 it is checked if the detection successful. If the measured current is not above the threshold, at step 238 it can be checked if the case 2 counter is at N+1. If not, the method can continue to execute the remaining logic (step 236). On the other hand if the case 2 counter is at N+1, the logic acts to reset the circuit breaker at step 234.
[0055] In a scenario wherein at step 222, if the measured current is above the threshold, at step 224 the counter can be reset by +1 and at step 226 it can be checked if the case 2 counter is more than or equal to N. If not, the logic can continue to measure the consecutive current samples of any of the phase having current above the threshold (step 218). On the other hand if the case 2 counter is more than or equal to N, it can correspond to satisfying the second case (step 228) and the logic can, at step 230, check the health of the FSD of the circuit breaker. In case it is detected that voltage of the FSD is in healthy condition, FSD can be triggered at step 232 to trip the circuit breaker. On the other hand if the voltage of the FSD is inadequate, the logic can go back to continue with the logic.
[0056] In accordance with the present disclosure, the steps described herein above can be executed by a microcontroller that can be configured to receive the detected peak current and conditioned analog signals either via an Analog-to-Digital Converter (ADC) or at ADC channels of the microcontroller.
[0057] In accordance with an embodiment, in the event that either the first condition or the second condition for confirming an overload condition is not satisfied, system and method of the present disclosure continues to sense successive samples of analog current signals associated with each circuit breaker at regular intervals.
[0058] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0059] The present disclosure mitigates short comings of conventional systems and methods for selectivity between circuit breakers connected in series in response to an overcurrent condition.
[0060] The present disclosure provides a system and method for selectivity between circuit breakers that is simple.
[0061] The present disclosure provides a system and method for selectivity between circuit breakers that is cost effective.
[0062] The present disclosure provides a system and method for selectivity between circuit breakers that is easily customizable from a single location.
[0063] The present disclosure provides a system and method for selectivity between circuit breakers that is reliable.
[0064] The present disclosure provides a scalable system and method for selectivity between circuit breakers.
[0065] The present disclosure provides a system and method for selectivity between circuit breakers such that there is no need for hard wired communication or signal transmission between the series connected circuit breakers.
[0066] The present disclosure provides a system and method for selectivity between circuit breakers that obviates need for signal interconnection between current measuring devices of the series connected circuit breakers.