Claims:1. A circuit breaker operatively coupled with an electronic trip unit (ETU), said circuit breaker comprising:
a microcontroller configured to:
check whether value of an incoming current is greater than a crossover value;
compute energy accumulation of incoming current as per short circuit characteristic curve or overload characteristic curve; and
generate an electronic trip command if the energy accumulation of incoming current is above a trip threshold value.
2. The circuit breaker of claim 1, wherein said microcontroller is further configured to sample the incoming current and implement root mean square (RMS) computation of the incoming current.
3. The circuit breaker of claim 1, wherein computation of energy accumulation adapts to short circuit characteristics in case of a crossover of fault current to prevent loss of selectivity.
4. The circuit breaker of claim 1, wherein computation of energy accumulation operates on per-cycle RMS value of current.
5. The circuit breaker of claim 1, wherein said microcontroller enables short circuit protection that provides fixed delay setting for better coordination of the ETU and a downstream circuit breaker and also inverse-time delay characteristics to achieve selectivity with the downstream circuit breaker.
6. The circuit breaker of claim 1, wherein said microcontroller comprises of a database that contains a plurality of overload protection following curves and thermal characteristics of an electrical system.
7. The circuit breaker of claim 6, wherein said plurality of overload protection following curves comprises of any or a combination of I2T, I4T, SI and VI curves wherein said plurality of overload protection following curves are configured to adapt to short circuit delay settings of fixed delay and inverse time characteristics and the curves are mapped to same range that allows different user settings to be considered at different times.
8. The circuit breaker of claim 6, wherein said plurality of overload protection following curves comprise of a common algorithm and tripping threshold in which the computation of energy accumulation is modified according to the selected curve.
9. A method for providing short circuit and overload protection to electrical systems, the method comprising the steps of:
checking whether value of an incoming current is greater than a crossover value;
computing energy accumulation of incoming current as per short circuit curve or overload curve; and
generating an electronic trip command if the energy accumulation of incoming current is above a trip threshold value.
10. The method of claim 9, wherein the method further comprises sampling of incoming current and implementing root mean square (RMS) computation of incoming current.
, Description:TECHNICAL FIELD
[0001] The present disclosure relates generally to circuit breakers for protecting electrical circuits against overload and short circuit conditions. In particular, the present invention relates to circuit breakers providing overload and short circuit protection with the help of electronic trip unit.
BACKGROUND
[0002] In a conventional distribution system, an upstream device has to play a dual role of primary protection as well as backup protection i.e. if a downstream device fails to clear the fault, the upstream device has to trip. This type of coordination can be achieved by properly maintaining selectivity between protection units. Thus, a combination of two or more protective devices are said to be selective when only the device closest to the fault detects and interrupts the fault current and the upstream breaker do not trip. Selectivity between devices in series provides good resistance against unwanted trips that can be caused by overloads or short-circuit currents to provide continual service.
[0003] Evidently, short circuit delay settings of circuit breaker helps in achieving selectivity between protective devices. Further, there are two types of delay settings for short circuit protection, viz. fixed delay time and inverse-time delay. In case of fixed delay setting, upstream breaker delays short circuit trip by a definite time, which helps in providing selectivity with a downstream breaker with electronic trip unit. A fuse has inverse time-current tripping characteristics, wherein in order to provide selectivity with the fuse, upstream breaker has to adhere to inverse time current curve. Thus, inverse-time delay setting in short circuit protection is useful to achieve selectivity with downstream fuse.
[0004] Overload protection is a basic overcurrent protection that is based on thermal characteristics on bus bars or feeder. Overload trip times are based on inverse definite minimum time (IDMT) curve settings given by IEC or IEEE standard, which settings for overload protection are configured to take care of thermal overload faults in which current is of lower magnitude compared to short circuit range. When a fault with higher current value occurs, corresponding trip time according to overload inverse curve goes below the time delay setting of short circuit. Hence, the upstream breaker trips while the fault is supposedly to be cleared by the downstream breaker. Therefore, selectivity is lost, which is a nuisance for other parallel downstream feeders. There is hence is a need for overload protection where thermal characteristics of bus bars and feeders are accurately replicated but at the same time maintain selectivity achieved by the short circuit time delay settings. Also, mechanisms are required to ensure that current fluctuations, especially in the overlapping region, should not cause any nuisance trip.
[0005] Prior art CA2214608C proposes design of distribution system using graphical method and transferring that information to individual protection units via communication network to coordinate all the units in the system. Further, this prior art provides a display that suggests the settings that are required to achieve coordination that is set either manually or through a communication interface in the trip units.
[0006] United States Patent US6603649B1 describes an electronic tripping device for a circuit breaker for simulating response curve of a fuse. The device can be controlled by a single setting mechanism representing nominal currents or rated currents of fuses to improve coordination of protection in sophisticated power supply equipment containing both circuit breakers and fuses.
[0007] United States Patent US4266259A provides two separate signal conditioning circuitry for overload and short time trip in such a way that during short circuit condition, overload trip circuit is bypassed, resulting in inverse short circuit trip. If the current level exceeds a fixed level, inverse overload and inverse short circuit circuitry is manipulated in such a way that short circuit signal conditioning circuit trips in fixed time.
[0008] United States Patent US20030156374A1 implements three levels of protection mechanism viz, an overload area, a short-delay short circuit area, and an undelayed short-circuit area to achieve selective coordination with current measurements using Rogowski coils.
[0009] As can be seen, these references disclose different circuit breakers providing overload and short circuit protection to electrical systems but none of them provide an electronic trip system that includes a single signal conditioning circuitry to monitor the current and use a thermal modelling approach to provide trip in different conditions.
[0010] There is therefore a need for an electronic trip system for circuit breakers providing overload and short circuit protection to electrical systems and overcome shortcomings of known systems.
OBJECTS OF THE INVENTION
[0011] A general object of the present disclosure is to provide overload and short circuit protection to various electrical systems.
[0012] Another object of the present disclosure is to provide a graphical representation of overload and short circuit conditions.
[0013] Another object of the present disclosure is to provide an electronic trip system that prevents the circuit in the event of a thermal overload, short circuit, or ground fault.
[0014] Another object of the present disclosure is to provide an electronic trip system where fluctuation in current signal does not result in a nuisance trip.
[0015] Another object of the present disclosure is to provide an electronic trip system where the system can generate instantaneous as well as delayed trip.
[0016] Another object of the present disclosure is to provide an electronic trip system that detects and selectively isolates fault current in an electrical system.
[0017] Another object of the present disclosure is to provide an electronic trip system that is cost efficient.

SUMMARY
[0018] Aspects of the present disclosure relates to a circuit breaker that is operatively coupled with an electronic trip unit (ETU) wherein said circuit breaker comprises of a microcontroller that is configured to check whether value of an incoming current is greater than a crossover value, compute energy accumulation of incoming current as per short circuit characteristic curve or overload characteristic curve, and generate an electronic trip command if the energy accumulation of incoming current is above a trip threshold value.
[0019] In an aspect, said microcontroller is further configured to sample the incoming current and implement root mean square (RMS) computation of the incoming current that is used to provide protections to the electrical system such as thermal overload and short circuit wherein if the protection unit senses a fault, it issues a trip command to the circuit breaker.
[0020] In an aspect, overload and short circuit protections have certain independent setting parameters to be configured by the user such as pickup threshold, delay setting, and curve selection. Further, overload and short circuit protection processes work independently as per their respective settings.
[0021] In an aspect, computation of energy accumulation operates on per-cycle RMS value of current and the computation adapts to short circuit characteristics in case of a crossover of fault current to prevent loss of selectivity. Further, short circuit protection can be configured for instantaneous trip or for different delay settings such as fixed delay or inverse curve setting. This feature allows the circuit breaker to delay before tripping on high level overcurrents resulting in maximum coordination i.e. achieve selectivity.
[0022] In an aspect, said microcontroller enables short circuit protection that provides fixed delay setting for better coordination of the ETU and a downstream circuit breaker and also inverse-time delay characteristics to achieve selectivity with downstream circuit breaker.
[0023] In another aspect, computation of energy accumulation depends on input variables such as current value, curve selection, etc. The energy value is continuously compared with the predefined threshold energy. If energy of any phase exceeds threshold energy, the protection unit issues a trip. The disclosed system takes into account current variation of each cycle and modifies trip time accordingly. Thus, when the current ramps up, energy of the conductors reaches threshold rapidly and trip time reduces. Similarly, when current value ramps down, trip time increases. Further, when current value goes below the overload pick-up, energy of the system is reduced because of negative feedback equations, to account for reduction in energy and no trip condition.
[0024] In an aspect, said microcontroller comprises of a database that contains a plurality of overload protection following curves and thermal characteristics of an electrical system wherein said plurality of overload protection following curves comprises of any or a combination of I2T, I4T, SI and VI curves and these curves are mapped to same range that allows different user settings to be considered at different times. Further, said plurality of curves are configured to adapt to short circuit delay settings of fixed delay and inverse time characteristics and said plurality of curves consist of a common algorithm and tripping threshold in which the computation of energy accumulation is modified according to the selected curve.
[0025] In an aspect, protection module determines the current value at which the predicted trip time of overload protection module and short circuit protection is equal. In other words, it is the fault current value at which overload inverse curve crosses short circuit curve and this fault current value is termed as crossover point. Further, overload protection module that works on energy accumulation method keeps regular track of crossover point value. The overload module updates the energy accumulation value at every cycle of the fault current. If the current value is less than the crossover value then the accumulation is updated as per the overload curve equation. But, if the current value is above the crossover value then the energy is accumulated according to the short circuit curve. In this way the overload module adapts the short circuit time delay characteristics if the current value is above the crossover value. Further, even if current is varying continuously below and above the crossover value, rate of accumulation depends on whether the current value in each cycle is above the crossover value or below it. Thus, the system ensures that the overload protection module never issues a trip command earlier than the short circuit module and hence achieves selectivity.

BRIEF DESCRIPTION OF THE DRAWINGS
[0026] 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.
[0027] FIG. 1 illustrates an exemplary system block diagram of microcontroller based protection unit in accordance with embodiments of the present disclosure.
[0028] FIG. 2 illustrates an exemplary representation of trip time curves and crossover point in accordance with embodiments of the present disclosure.
[0029] FIG. 3 illustrates an exemplary representation of proposed adaptable energy accumulation method for overload protection in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION
[0030] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such details 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.
[0031] Embodiments of the present disclosure relates to a circuit breaker that is operatively coupled with an electronic trip unit (ETU) wherein said circuit breaker comprises of a microcontroller that is configured to check whether value of an incoming current is greater than a crossover value, compute energy accumulation of incoming current as per short circuit characteristic curve or overload characteristic curve, and generate an electronic trip command if the energy accumulation of incoming current is above a trip threshold value.
[0032] In an aspect, said microcontroller is further configured to sample the incoming current and implement root mean square (RMS) computation of the incoming current that is used to provide protections to the electrical system such as thermal overload and short circuit wherein if the protection unit senses a fault, it issues a trip command to the circuit breaker.
[0033] In an aspect, overload and short circuit protections have certain independent setting parameters to be configured by the user such as pickup threshold, delay setting, and curve selection. Further, overload and short circuit protection processes work independently as per their respective settings.
[0034] In an aspect, computation of energy accumulation operates on per-cycle RMS value of current and the computation adapts to short circuit characteristics in case of a crossover of fault current to prevent loss of selectivity. Further, short circuit protection can be configured for instantaneous trip or for different delay settings such as fixed delay or inverse curve setting. This feature allows the circuit breaker to delay before tripping on high level overcurrents resulting in maximum coordination i.e. achieve selectivity.
[0035] In an aspect, said microcontroller enables short circuit protection that provides fixed delay setting for better coordination of the ETU and a downstream circuit breaker and also inverse-time delay characteristics to achieve selectivity with downstream circuit breaker.
[0036] In another aspect, computation of energy accumulation depends on input variables such as current value, curve selection, etc. The energy value is continuously compared with the predefined threshold energy. If energy of any phase exceeds threshold energy, the protection unit issues a trip. The disclosed system takes into account current variation of each cycle and modifies trip time accordingly. Thus, when the current ramps up, energy of the conductors reaches threshold rapidly and trip time reduces. Similarly, when current value ramps down, trip time increases. Further, when current value goes below the overload pick-up, energy of the system is reduced because of negative feedback equations, to account for reduction in energy and no trip condition.
[0037] In an aspect, said microcontroller comprises of a database that contains a plurality of overload protection following curves and thermal characteristics of an electrical system wherein said plurality of overload protection following curves comprises of any or a combination of I2T, I4T, SI and VI curves and these curves are mapped to same range that allows different user settings to be considered at different times. Further, said plurality of curves are configured to adapt to short circuit delay settings of fixed delay and inverse time characteristics and said plurality of curves consist of a common algorithm and tripping threshold in which the computation of energy accumulation is modified according to the selected curve.
[0038] In an aspect, protection module determines the current value at which the predicted trip time of overload protection module and short circuit protection is equal. In other words, it is the fault current value at which overload inverse curve crosses short circuit curve and this fault current value is termed as crossover point. Further, overload protection module that works on energy accumulation method keeps regular track of crossover point value. The overload module updates the energy accumulation value at every cycle of the fault current. If the current value is less than the crossover value then the accumulation is updated as per the overload curve equation. But, if the current value is above the crossover value then the energy is accumulated according to the short circuit curve. In this way the overload module adapts the short circuit time delay characteristics if the current value is above the crossover value. Further, even if current is varying continuously below and above the crossover value, rate of accumulation depends on whether the current value in each cycle is above the crossover value or below it. Thus, the system ensures that the overload protection module never issues a trip command earlier than the short circuit module and hence achieves selectivity.
[0039] FIG 1 illustrates an exemplary system block diagram of a microcontroller based protection unit 100, where a power supply unit 102 that derives power from incoming current is configured to power the protection unit 100. Signal conditioning circuit 104 processes the incoming current that is converted into a measurable signal and provided to AC to DC channels (using ADC 108) of microcontroller 106. A user interface module 112 can be provided that is responsible for interaction with user for configurations and status indication purposes.
[0040] In an aspect, the user interface 112 can be a display unit with keypads or a touchscreen that can allow user to access various configuration parameters as well as status indications.
[0041] In an aspect, microcontroller 106 includes a database 110 that can be configured to store various standard inverse definite minimum time (IDMT) curves and thermal characteristics of electrical system. Further, a tripping circuit 114 may be configured with the microcontroller 106 in a manner such that the tripping circuit 114 processes commands from the microcontroller 106 when it detects a fault, thereby being responsible for tripping circuit breaker.
[0042] FIG 2 illustrates an exemplary representation/graph of trip time curves and crossover point where 3 protection curves (202, 204, and 206) can be seen in the graph. In an aspect, lowermost curve 206 describes tripping characteristics of downstream protection device, whereas the other two curves 202 and 204 are overload and short circuit protection curves of the upstream protection unit respectively. It can be observed that when the fault current goes higher than ‘I1’, trip time, as per the overload protection curve 202, becomes lower than the short circuit protection curve 204. One exemplary purpose of short circuit curve 204 is to achieve coordination with the downstream tripping characteristics 206. Further, when the fault current is higher than ‘I1’ and close to ‘I2’, trip time of the upstream protection curve 202 comes in the tripping zone of the downstream device. Fault current higher than ‘I2’ makes the upstream breaker trip before the downstream device and hence, loses selectivity. The proposed invention takes care of the situation described in this graph by reliable methods of providing both the thermal overload protection as well as short circuit protection with total selectivity with downstream devices.
[0043] FIG 3 illustrates an exemplary representation of proposed adaptable energy accumulation method, and describes an exemplary process flow of working of overload protection module in the proposed protection unit. In an exemplary implementation, after the protection unit is powered on, analysis module 308 analyzes protection settings of both the overload and short circuit protection. Analysis is performed to predict crossover point 310, which is the point when fault current value at which overload protection curve crosses the short circuit characteristics. Further, a user interface 304 is provided that can be a display unit configured with keypads or touchscreen wherein if user changes/updates any parameter of protection settings 302 and 306 through the user interface 304, analysis module 308 performs re-computations to predict the updated crossover point 310. After updating constant parameters and crossover data, protection unit starts sampling the incoming current signal through AC to DC convertors 312. Thereafter, the sample values can be used for RMS computation of the current for each cycle 314, wherein conditional module 316 verifies if the computed current value is greater than the crossover value. In case the computed current value is lesser than the crossover value, energy accumulation process updates energy data according to overload inverse curve characteristics 320 and 322. But, if the current value of a cycle is greater than the crossover point, the computation indicates that fault current has entered the region below the short circuit curve. Hence, in this case, energy accumulation process updates energy data according to short circuit tripping characteristics 318 and 322. The updated energy accumulation data can then be compared with the tripping threshold 324, wherein if the updated energy accumulation data crosses the threshold, trip command is issued to trip the breaker and the incoming current is cut-off at step 326. Otherwise, if the updated energy accumulation data does not cross the threshold, the proposed method continues the same process of measuring the current and accumulating energy data depending on the current value. Further, even if current is varying continuously below and above the crossover value, rate of accumulation depends on whether the current value in each cycle is above the crossover value or below it. Thus, the system ensures that the overload protection module never issues a trip command earlier than the short circuit module and hence achieves selectivity.
[0044] 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
[0045] The present disclosure provides overload and short circuit protection to various electrical systems.
[0046] The present disclosure provides a graphical representation of overload and short circuit conditions.
[0047] The present disclosure provides an electronic trip system that prevents the circuit in the event of a thermal overload, short circuit or ground fault.
[0048] The present disclosure provides an electronic trip system where fluctuation in current signal does not result in a nuisance trip.
[0049] The present disclosure provides an electronic trip system where the system can generate instantaneous as well as delayed trip.
[0050] The present disclosure provides an electronic trip system that detects and selectively isolates fault current in an electrical system.
[0051] The present disclosure provides an electronic trip system that is cost efficient.