CLIAMS:1. A method for overload protection in an electrical device comprising the steps of:
selecting, for each region/time-slot of a standard load curve of said electrical device, an overload curve;
assigning, to said each region/time-slot of a standard load curve of said electrical device, a pick up value such that in case current through said electrical device is greater than said pickup value energy is accumulated, and in case said current through said electrical device is lower than said pickup value, said energy is reduced;
defining, for said electrical device, an overload threshold value; and
accumulating said energy during operation of said electrical device, wherein a tripping signal is issued sooner said accumulated energy is greater than said overload threshold value to cut off power supply.

2. The method of claim 1, wherein said overload curve for said region/time-slot is selected from a list of preloaded curves stored in a first database.

3. The method of claim 1, wherein said overload curve for said region/time-slot is selected by a user.

4. The method of claim 1, wherein said overload curve for said region/time-slot is selected automatically, wherein said selected overload curve is stored in a second database.

5. The method of claim 1, wherein said energy is accumulated at one or a combination of continuously, pre-defined time intervals, intermittently, periodically, or randomly.

6. The method of claim 1, wherein said overload curve is selected from one or a combination of I2t, I4t, SI and VI.

7. The method of claim 1, wherein different overload curves are selected for different regions/time-slots of said standard load curve of said electrical device.

8. The method of claim 1, wherein said standard load curve corresponds to time-current characteristics of said electrical load.
,TagSPECI:TECHNICAL FIELD
[0001] The proposed disclosure generally relates to systems and methods for microcontroller based overload protection in electrical installations. More specifically, the present disclosure relates to systems and methods for implementing overload protection by using different user selectable overload curves at different time slots and defining adjustable tripping characteristics that are adapted to continuously monitor electrical current and initiate tripping action as a function of user selected tripping characteristics and overload curves.

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] Electric load/circuits/appliances/devices are designed to operate in a range of rated current level. However, the supply power fed to electrical circuit/appliances may contain certain abnormalities such as voltage fluctuations and over voltage that may result in current overload.However, a more damaging situation of current overload may occur due to abnormalities such as short circuit, which have the potential of causing extensive damage to electrical equipment and installations.
[0004] Overload protection may be provided by electrical switching apparatus such as a fuse, a trip unit, or a circuit breaker in the circuit, or by means of protection that may be designed into the supply itself that is feeding the circuit. Different electric switching devices and circuit interrupters such as circuit breakers, trip unit, motor starters, motor controllers and other load controllers are used to protect electrical circuitry, appliances and equipment from damage due to abnormal conditions such as sudden voltage fluctuation, overload condition, or relatively high level short circuit or fault condition. The main function of any electrical switching apparatus such a circuit breaker is to ensurethat the rated current is not abnormally exceeded.
[0005] One of oldest and most common technical implementation for protection against overload is use of fusible wire that breaks the circuit by melting under conditions of overload. Subsequently trip units used bimetallic strips to provide overload protection. Bimetallic relays (thermal relay) coupled directly or through a current transformer to the main circuit are still in common use. For instance, Chinese Patents CN202930339U and CN201845724U talk about various bimetal based overload protection circuits, wherein the patent describes a circuit breaker overload protection device that comprises a heating element and a bimetallic sheet, that is provided with a contact, where the device includes an insulation sheet arranged between the bimetallic sheet and the heating element. It realizes the normal work of the circuit breaker overload protection device on account of heating to high temperature under conditions of overload.
[0006] With the advent of electronic trip units, analog circuits were initially used to detect overload conditions. For example, European patent EP0370139B1 talks about conversion of AC signals to corresponding DC values using hardware circuitry. These DC values described by EP0370139B1 are then compared with a predetermined threshold using a comparator circuitry and after detection of a fault (DC value exceeding predetermined threshold), a timer was used to provide some delay, and as the time elapsed, a trip signal was issued. However for this implementation, a separate timer was required and the disclosed method also suffers from the shortcoming of nuisance tripping due to sudden spikes. As an improvement over above method, some of the other techniquesknown in the art use loading of a timer according to the fault/overload current flowing through the conductors. After the trip time elapses, the controller issues a trip. These known overload protection methods typically operate on an inverse time curve, where the tripping time becomes less as overload current increases. The requirement and principle of an inverse time curve can be illustrated through an example. For illustration, let’s assume that the over-current value is 5A for 600ms for an electric motor. With this setting a current of 5A or higher, which is maintained through the motor for more than 600ms, will trigger the protection. However in this case, if the motor is supplied a current of 15.5A, the protection will still trigger only after 600ms and may cause the damage to the motor. Therefore, it becomes imperative to specify a shorter trip time for higher fault current known as time over current protection function. With time over current protection, increases in current above a continuous current rating are recognized and a trip signal is provided to a circuit breaker to interrupt power after time “t”, with the value of “t” depending upon the amount of the fault current. Typically, the response will be on an inverse time basis, i.e. the larger the fault current lesser the time to trip, in accordance with a particular inverse time-current curve. Time over current protection functions can be implemented with time overcurrent elements or electronically in a microprocessor (digital) relay.
[0007] In the above illustration, if we consider a worst case scenario where the motor is supplied 5A for 550ms and then 4.9A for 100ms, and then again 5A for 450ms and then 4.9A and so on, the result will be that the motor will overheat and burn without over-current protection getting triggered. Under such scenario, we can't use the current limit anymore to prevent the damage to the installation or equipment and we will require a thermal overload protection. Simplest known overload protection method based on thermal overload is a thermal safety switch that is arranged inside or is in connection with the motor where the switch trips after given temperatures limit is exceeded and interrupts the current flow through the installation. A more advanced version is an electronic unit that measures the temperature of the electric motor with temperature sensors and triggers a shut-off of the motor. These methods are directly based on temperature detection with various sensors. However the problem with this method is the difficulty of placing the sensors correctly. Also sensor based protection methods are relatively slow to react.
[0008] Another known overload protection method uses inverse time-current curves such as I2t curve to keep track of the temperature/thermal load of electrical loads/circuits/appliances/devices (such as motor) by monitoring electrical current and computing the likely temperature/thermal load. As this method depends on assessment of temperature/thermal load based on effect of accumulated energy calculated using current flowing through the installation/equipment, it is also known as accumulation method. Any current above the nominal value will produce a bigger or smaller thermal effect, but nevertheless overheat equipment/installation. Likewise, current below the nominal value will allow the motor to cool resulting in decrease in temperature (down to the ambient temperature in the best case = current zero = motor stopped). Depending on characteristics of the equipment, one of the various curves such as I2t, I4t, SI, and VI is selected to provide threshold value. When threshold is reached the protection is triggered.
[0009] US Patent US5418677 describes a similar method of overload protection that discloses an overload protection system for an electrical device, particularly an electric motor (M). The overload protection system of ‘677 measures current supplied to the electrical device (M), and calculates thermal load on the electrical device on the basis of the measured load current, and shuts off the current supply when thermal load reaches a given threshold level.
[00010] Various other overcurrent devices are known in the art for protecting electrical circuit/appliances/device from damage due to an excessive electrical current supplied or sudden load. Such overcurrent protection devices are typically characterized by their time-current characteristics or protection curves. Such protection curves are normally utilized to limit the temperature rise of an electrical conductor due to an excessive electrical current in order to prevent damage. For example, temperature rise of electrical conductors during certain excessive current conditions can be approximated by the product of the square of the electrical current and the time period for which electrical current is applied to the electrical conductors (e.g., I2t). These methods typically process data in numeric format, i.e. digitally using a microprocessor. The overload protection device measures the root mean square (rms) value of the phase currents (load currents) and this analogical measurement data are converted with an A/D converter into digital data. The actual measurement and protection functions are implemented by means of a microprocessor which calculates the temperature-dependent operating time.
[00011] The state of the art solutions use a single curve setting throughout the operation of the electric load for protecting the electrical circuits/appliances/devices whereas the current requirement varies depending on various conditions and timing. Therefore, there is a requirement to have different protections at different time slots according to the varying requirement of the circuit/appliances/device during its operation. For example a motor may require high starting current for some time, and thereafter a lower current for smooth running. Existing solutions are not optimal for time varying load requirement having different fault current levels. Many of the electrical loads as illustrated above have high starting current requirement. Once they start running, the current requirement drops. In most of the circuit breakers, either the pickup setting is kept higher than the starting current or few initial cycles are skipped, which can put the safety of instruments and personnel in danger. The operating fault current level varies based on the actual required current at different stage of appliance operation.Hence, it would be desirable to have a simple and effective way to provide a fast and safe tripping action using different overload protection curves for different time slots. There is therefore a need in the art for a microcontroller based thermal overload protection unit that works with different curves at different time slots in order to provide safety to the electrical loads/circuits/appliances/devices having varying current requirements.
[00012] 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.
[00013] 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.
[00014] 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.
[00015] 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.

OBJECTS OF THE INVENTION
[00016] It is an object of the present application to provide systems and methods for improved overload protection for electrical equipment.
[00017] It is an object of the present application to provide improved microcontroller based overload protection for electrical equipment.
[00018] It is another object of the present application to provide improved overload protection with multiple overload curves being used at different time slots.
[00019] It is another object of the present application to provide a system and method to calculate estimated energy accumulation over a period of time that is used to implement overload protection.
[00020] It is another object of the present application to provide an improved energy based accumulation algorithm.
[00021] It is another object of the present application to implement a system initiated signal for overload protection tripping.
[00022] It is yet another object of the present application to provide a merged curve implementation of different overload curves used at different time slots.
[00023] It is another object of the present application to provide user selectable curves and settings for overload protection.
[00024] It is another object of the present application to give the user an option to select different curves from internal database for different time slots.
[00025] It is another object of the present application to provide an overload protection to attached electrical loads/circuits/appliances/devices without using a timer.
[00026] It is yet another object of the present application to provide an overload protection to attached electrical loads/circuits/appliances/devices without using separate sensors.
[00027] Various objects, features, aspects and advantages of the present invention will become more apparent from the detailed description of the invention herein below along with the accompanying drawing figures in which like numerals represent like components.

SUMMARY OF THE INVENTION
[00028] Aspects of present disclosure relate to systems and methods for implementing efficient overload protection for electrical devices/loads. An aspect of the present disclosure relates to an accumulation based method for implementing overload protection by using different user-selectable curves including, but not limited to, I2t, I4t, SI and VI for different regions/time slots of a standard load curve for an electrical load. More particularly, the proposed systems and methods disclose microprocessor based overload protection with adjustable tripping characteristics that is adapted to continuously monitor electrical current flowing through the proposed overload protection unit, calculate accumulated energy, and initiate a trip as a function of a selectable tripping characteristic i. e. if the accumulated energy is higher than a defined threshold, based on user selected characteristics.
[00029] Another aspect of the present disclosure discloses a single improved energy accumulation method for different overload curves for implementing overload protection.
[00030] Yet another aspect of the present disclosure discloses user-selectable overload curves stored in a database such as an internal database of a microcontroller to be used at different time slots/regions of a standard load curve for an electrical load.
[00031] In order to further understand the techniques, means and effects of the present disclosure, the following detailed descriptions and appended drawings are hereby referred, such that, through which, the purposes, features and aspects of the present disclosure can be thoroughly and concretely appreciated; however, the appended drawings are merely provided for reference and illustration, without any intention to be used for limiting the present disclosure.
[00032] 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
[00033] 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.
[00034] FIG.1 illustrates an exemplary block diagram of microcontroller based thermal overload protection unit in accordance with the embodiment of the present disclosure.
[00035] FIG. 2 illustrates exemplary functional modules of the proposed overload protection system in accordance with an embodiment of the present disclosure.
[00036] FIG. 3 illustrates a flow chart of an exemplary microcontroller based thermal overload protection method in accordance with the embodiment of the present disclosure.
[00037] FIG.4illustratesan exemplary time-current characteristic of I2t curve.
[00038] FIG. 5 illustrates an exemplary time-current characteristic of I4t curve.
[00039] FIG. 6 illustrates a merged curve implementation of one or more user-selectable overload curves configured to operate at different times in accordance with an embodiment of the present disclosure.
[00040] FIG. 7 illustrates an exemplary flow chart for selecting overload curves and assigning pickup values for one or more regions/time slots of a standard load curve of an electrical device in accordance with a first embodiment of the present disclosure.
[00041] FIG. 8 illustrates an exemplary flow chart for selecting overload curves and assigning pickup values for one or more regions/time slots of a standard load curve of an electrical device in accordance with a second embodiment of the present disclosure.
[00042] FIG. 9 illustrates an exemplary flow chart for overload protection based on energy accumulation in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[00043] Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”
[00044] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[00045] As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.
[00046] The headings and abstract of the disclosure provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[00047] Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
[00048] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[00049] As mentioned above, existing overload protection devices use one or the other overload protection curves for an electronic circuit/appliances/device, whereas current requirement of electrical circuits/loads/appliances/devices vary depending on various conditions and timing. In some scenario, it is required to have different protection curves at different time slots according to the varying requirement of the electrical loads/circuit/appliances/devices during their operation.
[00050] Different embodiments herein will describe the different aspects of present disclosure for a microcontroller based thermal overload protection unit. The described embodiments relate to systems and methods for energy accumulation for implementing overload protection by using different selectable curves like I2t, I4t, SI, VI at different fault current levels at different time slots. More particularly, the proposed systems and methods relate to microprocessor based overload protection with adjustable tripping characteristics that is adapted to continuously monitor electrical current flowing through an overload protection unit, and initiate a trip as a function of a selectable tripping characteristic.
[00051] FIG. 1 illustrates an exemplary overall block diagram 100 of a microcontroller based thermal overload protection unit in accordance with an embodiment of the present disclosure. According to one embodiment of the overload protection system and method, power supply system 110 can be used to power up one or a combination of signal conditioning system 130, a microcontroller 120, and a trip circuit 150. Signal conditioning system 130 can be configured to provide DC shifted AC output to ADC 122 of the microcontroller 120, wherein the microcontroller 120 can process the signal and detect whether an overload fault is present. In case it is detected that an overload condition is present, the microprocessor 120 gives a command to trip circuit 150 to start the trip mechanism (also referred to as “tripping action” or simply as “tripping”) of circuit breaker.
[00052] In another aspect, microcontroller 120 can estimate energy of the conductor by using energy accumulation method that is further used to implement overload protection. Energy of the conductor can be calculated and accumulated at regular intervals, wherein the value of accumulated energy gives an indication of heating of the conductor. Microcontroller 120 can continuously compare the accumulated energy with a predefined cutoff threshold energy set for the attached electrical load/circuit/appliance/device such that if the accumulated energy exceeds the predefined threshold energy, the controller 120 issues a trip signal to the trip circuit 150. In an aspect, energy calculation can depend on different user-selected overload curves for different time slots during the operation of the attached electrical circuit/appliance/device being protected. The energy calculation can therefore depend on the user selectable overload curves such as I2t, I4t, SI and VI, and the current input. A user can select different overload curves from the known curves (that can be stored, for instance, in a database) depending on the requirement at different fault current levels for different time slots.
[00053] In another aspect, if the current ramps up, energy of the conductor(s) reaches the defined energy consumption threshold fast/quickly and the trip time reduces. Similarly, if the current value ramps down, the trip time increases. If the current value goes below a set limit (pick-up value), energy of the system can be reduced by applying negative feedback equations to account for reduction in energy and no trip condition. The proposed system and method istherefore sensitive to current fluctuations of the conductor and represents a true picture of the current flowing through them. Cooling time of the conductors can be decided based on the input provided by the user. Also, the energy of the system is calculated for each set time interval and then accumulated with previous interval energies, any fluctuation in the current can be accounted for, and hence trip time can be modified accordingly. The method presented here, as a result, eliminates the problem of current ramp up or ramp down.
[00054] In an embodiment, a user may decide which overload curve protection the system should use and in what condition or at what time. The user may choose to provide different curve protections at different time slots and the accumulated energy can be calculated accordingly.
[00055] In an embodiment, user may select a standard load curve for an electrical device/load from the list of preloaded standards load curves stored in, for instance, a database DB124 of the microcontroller 120, wherein standard load curves are referred to as current-time curves recommended for different electrical circuits/appliances/devices, through the user interface 140. In one aspect, each standard load curve for an electrical device can be divided into a plurality of regions such that, in an exemplary implementation/embodiment, an overload curve can be selected by the user for each region (also interchangeably referred to as time slot hereinafter) of the standard load curve, enabling a situation wherein the complete standard load curve can be assigned a plurality of overload curves based on the characteristics of each region/time slot of the standard load curve. In an embodiment, a user interface 140can be attached to the thermal overload protection unit’s microcontroller 120 through suitable means.
[00056] According to another embodiment, the user may enter different overload curve characteristics through a suitable interface to be used at different time slots/regions and store these details in the database DB124. The user can also select some of the standard defined curves for few loads from internal database. One should appreciate that overload curves, standard load curves, pickup values, and thresholds can be stored in any database present locally or remotely and any change in configuration is completely within the scope of the instant disclosure.
[00057] According to another embodiment, trip time can depend on user-selectable overload curves including, but not limited to, I2t, I4t, SI, VI, wherein a person skilled in the art will appreciate that one algorithm and one tripping threshold can be used for all the curves and only the inputs can be modified based on the selected overload curve. Any other such change in configuration is also completely within the scope of the present disclosure. All the overload curves can be mapped to a common range that allows different user settings to be considered at different times. The overall code size for the protection can be reduced due to common algorithm. Also, since the expected values of current are predetermined and pre-informed to the trip circuit150, any deviation from the normal current flow can be notified and the electrical device/load can always be protected irrespective of the load connected and settings done. One should appreciate that although most of the present disclosure explains embodiment that detail manual/user-based assignment of multiple overload curves based on time slot, the complete or any part of the entire system/method of the present disclosure can be automated or partially automated, and therefore any such automation is completely within the scope of the instant disclosure.
[00058] FIG. 2 illustrates exemplary functional modules of the proposed overload protection system 200 in accordance with an embodiment of the present disclosure. In an exemplary implementation, system 200 of the present disclosure can include, but not limited to a, overload assignment module 202 configured to assign a plurality of overload curves (such as I2T, I4T, SI, VI) to a region/time slot of a standard load curve of an electrical device/load based on the overload curves that can best define the behavior of the electrical device/load during that region/time slot.
[00059] In another implementation, system 200 can further include a pickup value assignment module 204 configured to assign, to each region/time slot of the standard load curve of the electrical device, a pickup value. In an exemplary implementation, the pickup value can be defined such that in case the current is greater than the pickup value, the energy is accumulated, whereas in case the current is lower than the pickup value, the energy is reduced. Therefore, when the current ramps up, i.e. goes beyond pick- up value corresponding to that time slot, the energy is added to the accumulated value. Conversely, if current value goes below the pick-up value, accumulated energy of the system is reduced by application of negative feedback equations, to account for cooling. The proposed method is therefore sensitive to current fluctuations of the conductor and represents a true picture of the current flowing through them. The cooling time of the conductors can be decided based on the input provided by the user. Also, since the energy of the system is calculated for each interval and then accumulated with previously accumulated energy, any fluctuation in the current is accounted for.
[00060] In yet another implementation, system 200 can further include an overload threshold value determination module 206 configured to determine and associate an overload threshold value to the attached electrical load/ circuit/ appliance/ device/ load. System 200 can further include an energy accumulation module 208 configured to calculate accumulated energy at predefined or random or any other defined time intervals during the operation of the electrical load. In implementation, based on the overload curve characteristics set by the user, microcontroller of the proposed system 200, can be enabled by the module 208 to calculate accumulated energy throughout the operation of the electrical load/circuit/appliance.
[00061] In another implementation, system 200 can further include an overload determination module 210 configured to determine as to whether the accumulated energy(computed by module 206)is greater than the set overload threshold value, wherein if at any time, the accumulated energy is greater than set overload threshold value (also referred to as predefined tripping threshold hereinafter), microcontroller 120 can issue a tripping signal to trip the circuit 150 and cut off the power supply. In an alternate embodiment, if the module 210 determines that the accumulated energy has not exceeded the tripping threshold, it continues to calculate and accumulate energy for each interval through module 208 till either the energy becomes higher than the tripping threshold or the electrical device/load is turned off.
[00062] FIG. 3illustratesan exemplary flow chart of microcontroller based overload protection method in accordance with an embodiment of the present disclosure. At 302,a user assigns a plurality of overload curves to different region/time slots of a standard load curve based on the overload curve that can best define the behavior of the electrical device/load during that region/time slot. At step 304, a pickup value can be assigned to each region/time slot. In an exemplary implementation, the pickup value can be defined such that in case the energy is greater than the pickup value, the energy is accumulated, whereas in case the energy is lower than the pickup value, the energy is reduced. Therefore, when the current ramps up, i.e. goes beyond pick- up value corresponding to that time slot, the energy is added to the accumulated value. Conversely, if current value goes below the pick-up value, accumulated energy of the system is reduced because of negative feedback equations, to account for cooling. The proposed method is therefore sensitive to current fluctuations of the conductor and represents a true picture of the current flowing through them. The cooling time of the conductors can be decided based on the input provided by the user. Also, since the energy of the system is calculated for each interval and then accumulated with previous interval energies, any fluctuation in the current is accounted for.
[00063] According to one embodiment, during the step 302, the user may select a standard overload curve from a list of preloaded recommended curves for different electrical circuit/appliances/devices, through a means/interface provided on the user interface/computing device 140 (as explained at Figure 7). In an alternate embodiment, the user may himself/herself enter through the interface, different overload curve characteristics to be used at different time slots/regions with corresponding pick up values and store these details in a database such as DB 124(as explained at Figure 8).
[00064] At 306, an overload threshold value that is applicable to the attached electrical load/circuit/appliance/device/ load can be set/defined by the user (or by any other appropriate means). At step 308, accumulated energy can be computed at predefined or random or any other defined time intervals during the operation of the electrical load. In implementation, based on overload curve characteristics set by the user, microcontroller of the proposed system can be configured to calculate accumulated energy throughout the operation of the electrical load/circuit/appliance. At step 310, a determination is made as to whether the accumulated energy is greater than the set overload threshold value, wherein if anytime, the accumulated energy is greater than predefined tripping threshold, microcontroller 120, as illustrated at step 312 issues a tripping signal to trip the circuit 150 and cutoff the power supply. In an alternate embodiment, if during the comparison at step 310, the microcontroller finds that the accumulated energy has not exceeded the tripping threshold, it continues to calculate and accumulate energy and therefore goes back to step 308.
[00065] FIG. 4illustratesan exemplary time-current characteristic ofI.sub.2t.(I2t) overload curve, which represents the product of the square of the current and the time, whereas FIG. 5illustratesyet another exemplary time-current characteristic of I.sup.4t (I4t) overload curve, which represents the product of the fourth power of the current and the time; I4t. A comparison of these exemplary curves illustrates the manner in which use of different overload curves affects the tripping time. Use of different curves at different time slots of operation of the installation characterized by different current requirements results in better overload protection when compared with known over current protection methods, which employ fixed characteristics such as general I2t characteristic.
[00066] FIG. 6illustratesa merged curve implementation 600 of one or more selectable overload curves (a, b, and c) configured to operate at different time slots in accordance with an embodiment of the present disclosure. In an embodiment, in view of FIG. 6, a standard load curve depicts the time-current characteristics of an electrical load with various overload protection curves. A user may choose different overload curves for overload protection at different time slots in accordance with the operating condition of the time slot. For example, a motor has high starting current that lasts for some time specified by the user. Therefore, for this duration, an overload curve such as I2thaving a higher trip delay setting can be used. After some time, when the current requirement reduces, the user for better protection may choose to switch from I2t to I4t curve or any other curve that signifies a smaller trip delay. As illustrated in FIG. 6, standard load curve ‘d’ is an exemplary characteristic of the electrical load/circuit/appliance/device such as motor. In this illustration, a user may choose different standard overload curves (‘a’, ‘b’, ‘c’) for use at different operating time slots. For example, curve 'a' can be selected till time t1, curve 'b' can be selected till t2, and curve 'c' thereafter(till the device operates/functions) shall provide best overload protection.
[00067] FIG. 7 illustrates an exemplary flow chart 700 for selecting overload curves and assigning pickup values for one or more regions/time slots of a standard load curve of an electrical device in accordance with a first embodiment of the present disclosure. At first step 702, a user or any other automated entity can enter time-current characteristic (standard load curve details) of an electrical load for which overload protection is to be performed. At step 704, entered time-current characteristic can be processed with respect to multiple standard load curves within a database or any other format of repository to retrieve applicable standard load curve for the electrical load. At 706, based on the loaded/retrieved standard load curve, a plurality of overload curves that best fit the standard load curve of the attached electrical load can be identified and fitted with respect to different time slots/regions of the standard load curve. At708, the assigned and fitted overload curves can be verified and reviewed for any modification/change/deletion of the fitment.
[00068] At step 710, for each region/time slot, a pickup value (overload current values) can be assigned by the user/entity. For instance, pickup current value P1 can be assigned with region 1 for time slot t1 (corresponding to overload curve_1), pickup P2 can be assigned with region 2 for the time slot t2(corresponding to overload curve_2), and so on. In an implementation, all pickup values, overload curve assignment, among other details/settings can be stored in an appropriate database.
[00069] At step 712, microcontroller or controller of the proposed overload protection circuit/system/apparatus can calculate root mean square (RMS) of the current passing through
the conductor. At step 714, time slot to which the RMS value belongs can be determined. At step 716, pickup value and overload curve for the determined time slot can be identified for energy calculations, which are further detailed in FIG. 9hereinafter.
[00070] FIG. 8 illustrates an exemplary flow chart 800 for assigning overload curves and assigning pickup values for one or more regions/time slots of a standard load curve of an electrical device in accordance with a second embodiment of the present disclosure. At first step 802, a user can retrieve already stored time-current characteristic (standard load curve details) of an electrical load for which overload protection is to be performed and can manually assign overload curves to regions/time slots of the standard load curve. At step 804, assigned overload curves are stored in data base. At 806, the assigned and fitted overload curves can be verified and reviewed for any modification/change/deletion of the fitment.
[00071] At step 808, for each region/time slot, a pickup value can be assigned by the user/entity. For instance, pickup current value P1 can be assigned with region 1 for time slot t1 (corresponding to overload curve_1), pickup P2 can be assigned with region 2 for the time slot t2 (corresponding to overload curve_2), and so on. In an implementation, all pickup values, overload curve assignment, among other details/settings can be stored in an appropriate database.
[00072] At step 810, microcontroller or controller of the proposed overload protection circuit/system/apparatus can calculate root mean square (RMS) of the current passing through the conductor, whereas, at step 812, time period to which the RMS value belongs can be determined. At step 814, pickup value and overload curve for the determined time period can be identified for energy calculations, which are further detailed in FIG. 9 hereinafter.
[00073] Figure 9illustrates a flow chart for energy accumulation method in accordance with the embodiment of the present disclosure. Flow chart explains the overload algorithm used for energy calculations after the pickup and overload curve settings are fixed. According to the curve and delay settings selected/entered by the user, values of constants to be used in equations are calculated as first step902.At next step 904,the microcontroller calculates the expected energyEE1 for the current flowing through the conductor. This value varies according to curve selected. At next step 906 the current flowing through the conductor is compared with the pickup value assigned to the time slot.In an embodimentif the current is greater than the assigned pickup value microprocessor at step 908 calculates the energy for the interval based on current and assigned curve setting for the time slot and accumulates the calculated energy with previous value CE1 to arrive at modified value of CE1.In an alternate embodiment if the current flowing through the conductor is less than the assigned pickup value, the microprocessor at step 910, checks whether the ratio of previous calculated energy CE1 to expected energy EE1 is greater than 1.Ratio greater than 1 signifies that current has reduced and therefore the energy is expected to reduce. If yes, then at step 912, negative feedback equations are used to reduce the calculated energy CE. Ratio less than 1signifies that calculated energy is less according to the current flowing through the conductors and therefore energy accumulation principle is to be used which is done at step 914 and is similar to step 908.
[00074] After calculation of energy in accordance with algorithm 900 explained above the procedure as outlined in FIG. 2 at steps 306 through 310 can be followed i. e. it can be checked (step 310) whether the energy of any interval is greater than the tripping threshold as set by the user at step306. If the accumulated energy at the end of any interval exceeds the set threshold, a trip signal can be issued by the microcontroller to stop the power supply 312.In case accumulated energy is less than tripping threshold, energy calculation 308 can be continued for next interval to calculate accumulated energy till the accumulated energy exceeds the set threshold or operation of equipment is stopped.
[00075] The above description represents merely an exemplary embodiment of the present invention, without any intention to limit the scope of the present invention thereto. Various equivalent changes, alterations or modification based on the present invention are all consequently viewed as being embraced by the scope of the present invention.
[00076] As used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Within the context of this document terms "coupled to" and "coupled with" are also used euphemistically to mean “communicatively coupled with” over a network, where two or more devices are able to exchange data with each other over the network, possibly via one or more intermediary device.
[00077] 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 subject 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 “comprises” and “comprising” 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 refers 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.

ADVANTAGES OF THE INVENTION
[00078] The present disclosure provides an improved overload protection method based on accumulation method.
[00079] The present disclosure provides an improved microcontroller based overload protection unit.
[00080] The present disclosure provides an improved overload protection method with multiple overload curves being used for different time slots.
[00081] The present disclosure provides a method to calculate estimated energy accumulation over a period of time that is used to implement overload protection.
[00082] The present disclosure implements a software initiated signal for overload protection tripping.
[00083] The present disclosure provides a merged curve implementation of different overload curves used at different time slots.
[00084] The present disclosure provides user selectable overload curves and settings for overload protection.
[00085] The present disclosure gives the user option to select different overload curves from internal database for different time slots.
[00086] The present disclosure provides overload protection to attached electrical loads/circuits/appliances/devices without using a timer.
[00087] The present disclosure provides overload protection to attached electrical loads/circuits/appliances/devices without using separate sensors.