Claims:1. A system for assessing health of a circuit breaker, said system comprising:
a memory operatively coupled to a microprocessor and comprising a set of instructions embodied in the memory that is executable by the microprocessor to:
calculate value of MA2S per interruption for any of R, Y and B input phases, wherein MA2S per interruption is a function of fault current during arcing of contacts of the circuit breaker and the duration of arcing;
calculate value of accumulated MA2S, wherein accumulated MA2S is a function of the value of MA2S per interruption, a breaker type constant and the fault current variable;
determine the maximum MA2S capacity of the circuit breaker, wherein maximum MA2S is a function of type of circuit breaker, size of the contacts of the circuit breaker and the material of the contacts of the circuit breaker; and
determine remaining life of circuit breaker based on ratio of accumulated MA2S value and the maximum MA2S capacity, wherein the remaining life of the circuit breaker is indicated on a display.
2. The system as claimed in claim 1, wherein the fault current variable is a function of an exponent of the fault current.
3. The system as claimed in claim 1, wherein the value of breaker type constant and the exponent are determined based on experimental observation of MA2S per interruption of the circuit breaker for at least two fault currents.
4. The system as claimed in claim 1, wherein the microprocessor is configured to determine a maximum possible contact operation of the contacts of the circuit breaker based on a ratio of maximum MA2S capacity to the MA2S per interruption for the circuit breaker.
5. The system as claimed in claim 1, wherein the microprocessor is configured to indicate if the circuit breaker is to be replaced based on the remaining life of the circuit breaker.
6. The system as claimed in claim 1, wherein said system is configured to store the calculated values of MA2S per interruption, accumulated MA2S and the determined maximum MA2S capacity in a memory operatively coupled to the system.
7. A method for assessing health of a circuit breaker, said method comprising the steps of:
calculating, at a computing device, value of MA2S per interruption for any of R, Y and B input phases, wherein MA2S per interruption is a function of fault current during arcing of contacts of the circuit breaker and the duration of arcing;
calculating, at a computing device, value of accumulated MA2S, wherein accumulated MA2S is a function of the value of MA2S per interruption, a breaker type constant and the fault current variable;
determining, at a computing device, the maximum MA2S capacity of the circuit breaker, wherein maximum MA2S is a function of type of circuit breaker, size of the contacts of the circuit breaker and the material of the contacts of the circuit breaker; and
determining, at a computing device, remaining life of circuit breaker based on ratio of accumulated MA2S value and the maximum MA2S capacity, wherein the remaining life of the circuit breaker is indicated on a display.
8. The method as claimed in claim 7, wherein the value of breaker type constant and the exponent are determined based on experimental observation of MA2S per interruption of the circuit breaker for at least two fault currents.
9. The method as claimed in claim 7, wherein a maximum possible contact operation of the contacts of the circuit breaker is determined based on a ratio of maximum MA2S capacity to the MA2S per interruption for the circuit breaker.
10. The method as claimed in claim 7, wherein an indication is provided to replace the circuit breaker based on the remaining life of the circuit breaker.
, Description:TECHNICAL FIELD
The present disclosure relates generally to monitoring health of a circuit breaker. In particular, the present disclosure relates to assessing remaining life of a circuit breaker.

BACKGROUND
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.
An Air Circuit Breaker (ACB) is an electrical device used to provide over current and short-circuit as well voltage-based protection for electric circuits. The circuit breaker is a combination of electronic and mechanical components. An electronics trip unit is the part of a circuit breaker that senses the fault current and gives a command to open the circuit in the event of overload, short circuit or ground fault. The electronics trip unit can be considered as a brain of the circuit breaker, and it continuously monitors current and voltage of the bus bar and acts instantaneously when it detects any fault in the system.
In the air circuit breaker, a leading cause for aging is the degradation of breaker mechanism due to increasing number of open and close operations. The level of interrupted current during each operation increases the impact on breaker contact. The service life of the circuit breaker depends on how much its contacts are wearing as a result of interrupt operations. Hence, to optimize the service life of the breaker, systematic checks and periodic maintenance of the breaker is required.
There is therefore a requirement in the art for a means to evaluate the health of a circuit breaker and recommend a remedial action based on the evaluation.
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.
In some embodiments, the numbers expressing quantities or dimensions of items, 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.
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.
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.
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 groups used in the appended claims.
OBJECTS
A general object of the present disclosure is to provide a system and method for assessing health of a circuit breaker.
Another object of the present disclosure is to provide a system and method for assessing health of a circuit breaker that does not require additional external hardware.
Another object of the present disclosure is to provide a system and method for assessing health of a circuit breaker that does not require measurement of arcing time and system voltage.
Another object of the present disclosure is to provide a system and method for assessing health of a circuit breaker that is accurate.
Another object of the present disclosure is to provide a system and method for assessing health of a circuit breaker that is economical.

SUMMARY
The present disclosure relates generally to monitoring health of a circuit breaker. In particular, the present disclosure relates to assessing remaining life of a circuit breaker.
In an aspect, the present disclosure provides a system for assessing health of a circuit breaker, said system comprising: a memory operatively coupled to a microprocessor and comprising a set of instructions embodied in the memory that is executable by the microprocessor to: calculate value of MA2S per interruption for any of R, Y and B input phases, wherein MA2S per interruption is a function of fault current during arcing of contacts of the circuit breaker and the duration of arcing; calculate value of accumulated MA2S, wherein accumulated MA2S is a function of the value of MA2S per interruption, a breaker type constant and the fault current variable; determine the maximum MA2S capacity of the circuit breaker, wherein maximum MA2S is a function of type of circuit breaker, size of the contacts of the circuit breaker and the material of the contacts of the circuit breaker; and determine remaining life of circuit breaker based on ratio of accumulated MA2S value and the maximum MA2S capacity, wherein the remaining life of the circuit breaker is indicated on a display.
In an embodiment, the fault current variable is a function of an exponent of the fault current.
In another embodiment, the value of breaker type constant and the exponent are determined based on experimental observation of MA2S per interruption of the circuit breaker for at least two fault currents.
In another embodiment, the microprocessor is configured to determine a maximum possible contact operation of the contacts of the circuit breaker based on a ratio of maximum MA2S capacity to the MA2S per interruption for the circuit breaker.
In another embodiment, the microprocessor is configured to indicate if the circuit breaker is to be replaced based on the remaining life of the circuit breaker.
In another embodiment, the system is configured to store the calculated values of MA2S per interruption, accumulated MA2S and the determined maximum MA2S capacity in a memory operatively coupled to the system.
In an aspect, the present disclosure provides a method for assessing health of a circuit breaker, said method comprising the steps of: calculating, at a computing device, value of MA2S per interruption for any of R, Y and B input phases, wherein MA2S per interruption is a function of fault current during arcing of contacts of the circuit breaker and the duration of arcing; calculating, at a computing device, value of accumulated MA2S, wherein accumulated MA2S is a function of the value of MA2S per interruption, a breaker type constant and the fault current variable; determining, at a computing device, the maximum MA2S capacity of the circuit breaker, wherein maximum MA2S is a function of type of circuit breaker, size of the contacts of the circuit breaker and the material of the contacts of the circuit breaker; and determining, at a computing device, remaining life of circuit breaker based on ratio of accumulated MA2S value and the maximum MA2S capacity, wherein the remaining life of the circuit breaker is indicated on a display.
In an embodiment, the value of breaker type constant and the exponent are determined based on experimental observation of MA2S per interruption of the circuit breaker for at least two fault currents.
In another embodiment, a maximum possible contact operation of the contacts of the circuit breaker is determined based on a ratio of maximum MA2S capacity to the MA2S per interruption for the circuit breaker.
In another embodiment, an indication is provided to replace the circuit breaker based on the remaining life of the circuit breaker.
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 DRAWINGS
The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain the principles of the present invention.
FIG. 1 illustrates an exemplary block diagram representing a typical interfacing of an electronics trip unit with a circuit breaker.
FIGs. 2A and 2B illustrate waveforms depicting voltage and current characteristics respectively during opening of the contacts of the circuit breaker to interrupt a fault in the circuit.
FIG. 3 illustrates a plot depicting arcing voltage.
FIGs. 4A and 4B illustrate plots of let-through energy per interruption and the corresponding calculated remaining life of circuit breaker respectively.
FIG. 5 illustrates an exemplary flow diagram for a method to determine remaining life of a circuit breaker.

DETAILED DESCRIPTION
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.
If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
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.
Exemplary embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. These exemplary embodiments are provided only for illustrative purposes and so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those of ordinary skill in the art. The invention disclosed may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Various modifications will be readily apparent to persons skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the invention. Moreover, all statements herein reciting embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Also, the terminology and phraseology used is for the purpose of describing exemplary embodiments and should not be considered limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous alternatives, modifications and equivalents consistent with the principles and features disclosed. For purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail so as not to unnecessarily obscure the present invention.
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.
The present disclosure provides a system and method to optimize service life of a circuit breaker. The system is inbuilt in the electronics trip unit and comprises the steps of measurement of fault current, measurement of the current at time of interruption and calculation of total I2T loss. A formula is derived which gives relationship between the fault current, I2T loss and remaining life of the contact. The hardware and firmware is designed in such a way that the remaining life of the breaker contact can be shown on a display and a notification for necessary action can be indicated, which can optimize the circuit breaker life.
FIG. 1 illustrates an exemplary block diagram representing a typical interfacing of an electronics trip unit with a circuit breaker. The R, Y, B primary bus bars are connected to the circuit breaker, which, in turn, is connected to the electronics trip unit along with a display.
FIGs. 2A and 2B illustrate waveforms depicting voltage and current characteristics respectively during opening of the contacts of the circuit breaker to interrupt a fault in the circuit. It can be seen that, when the circuit breaker closes at time t=0, voltage across its contacts is zero and a current starts flowing. When the current is interrupted at t=1, the current becomes zero and the voltage rises. The interruption of fault current can generate an arcing between the contacts, which can result in wearing of the contacts.
FIG. 3 illustrates a plot depicting arcing voltage. The arcing time can be measured from this plot. The total let-through energy can be calculated as,
E=?_(t=0)^8¦(I ×I × t)
where, I is the fault current at the time of arcing; and t is the duration of arcing. The total energy loss in one interruption can be expressed in Mega Ampere Square Second (MA2S).
Maximum life of circuit breaker = maximum MA2S capacity of circuit breaker contact

This can depend on the type of circuit breaker, size of the contacts and the material of the contacts.
% remaining life of circuit breaker = [1-(accumulated MA2S value )/(Max.MA2S value)]×100

The value of accumulated MA2S value is calculated as,
Y=C×X^2
where, Y is the MA2S value per interruption; C is the breaker type constant; and X is the fault current.

Table – 1 below provides practical data for the above values required to calculate % remaining life of the circuit breaker.

Fault Current (KA) MA2S per interruption Maximum operations possible with contact MAX MA2S Value
10 0.69 80 55.2
30 6.37 8 50.96
50 22.18 3 66.54
57.56666667

Illustrative Example:
Taking any two values from Table -1 and plugging them into the equations previously described,
0.69=C×?10?^b?(1)
6.3=C×?30?^b?(2)

Taking log on both sides of eq. (1),
log??0.69?=log?(C×?10?^b )
0.161=log??C ?+b log?10?(3)

Taking log on both sides of eq. (2),
log??6.3?=log?(C×?10?^b )
0.8=log??C ?+b log?30?(4)

Resolving eq. (3) and eq. (4),
b = 2; C = 0.007

Plugging in the above values in the main equation,
Y=0.007×X^2
Table – 2 below provides exemplary values for the above variables,
X Y Life
5 0.175 314.2857 2.497325
10 0.7 78.57143 1.895265
15 1.575 34.92063 1.543082
20 2.8 19.64286 1.293205
25 4.375 12.57143 1.099385
30 6.3 8.730159 0.941022
35 8.575 6.413994 0.807129
40 11.2 4.910714 0.691145
45 14.175 3.880071 0.58884
50 17.5 3.142857 0.497325
55 21.175 2.597403 0.414539
60 25.2 2.18254 0.338962
65 29.575 1.859679 0.269438
70 34.3 1.603499 0.205069
75 39.375 1.396825 0.145142
80 44.8 1.227679 0.089085
85 50.575 1.087494 0.036427

Using the above method, by measuring only the value of fault current, contact wear can be estimated and the remaining life of the circuit breaker can be calculated.
FIGs. 4A and 4B illustrate plots of let-through energy per interruption and the corresponding calculated remaining life of circuit breaker respectively.
FIG. 5 illustrates an exemplary flow diagram for a method to determine remaining life of a circuit breaker. The method can be embedded in a firmware of a computing device. The firmware logic is as follows,
power on the computing device and start.
initialise ADC channels for Current and voltage R, Y and B phases, including all other Buffers and Global variables with peripherals.
observe values MA2S for R, Y and B phases and store in Buffers (Arrays) at 10KA and 30KA.
based on any one of the phases, calculate Max. Threshold MA2S values at 10KA and 30KA and store in a permanent memory.
initialize 1.25Msec ISR routine by using Timer for measuring 16 Samples per cycle.
initialize 5Msec ISR routine by using Timer for Scheduler purpose. Scheduler starts to execute the all task with priority.
capture a sample for metering and Protection purpose.
if Fault current is detected, then calculate the MA2S values, C & b (Constant values) at two different 10KA and 30KA supplied currents.
if Calculated MA2S value is greater than a pre-set max. Threshold value, then on a display, indicate “Life of Contact Wear Over” and “Please change the Contact Wear”
else indicate on display Remaining life of Contact Wear, by expressing remaining Life In “%”. Store the value in permanent memory.
count the Number of Trip and store it in Permanent memory.
repeat the operation continuously.

Thus, the present disclosure provides a microprocessor-based trip unit to automatically detect fault current and calculate contact wear. Further, remaining life of contact can be estimated, and indicated on a display. The proposed system requires no external hardware as the entire system is inbuilt in the electronic trip unit. Further measurement of arcing time and system voltage is not required as the proposed system uses a single formula to define a relationship between fault current and breaker contact life. The proposed system provides an economic means to determine remaining life of the circuit breaker.
It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive patient matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “includes” and “including” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refer to at least one of something selected from the group consisting of A, B, C ….and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc. The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practised with modification within the spirit and scope of the appended claims.
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
The present disclosure provides a system and method for assessing health of a circuit breaker.
The present disclosure provides a system and method for assessing health of a circuit breaker that does not require additional external hardware.
The present disclosure provides a system and method for assessing health of a circuit breaker that does not require measurement of arcing time and system voltage.
The present disclosure provides a system and method for assessing health of a circuit breaker that is accurate.
The present disclosure provides a system and method for assessing health of a circuit breaker that is economical.