Claims:1. A self-powered electronic trip unit for a circuit breaker, said trip unit comprising:
a first controller operatively connected to a second controller, said first controller further comprising an analog-to-digital converter (ADC) and a first data flash module;
wherein the first controller is adapted to sense current and voltage signals, and implementing protection mechanisms;
wherein the first controller is adapted to generate trip records, event log, energy accumulation;
the said second controller further comprising a second data flash module;
wherein the second controller is a display controller;
wherein the said second controller is operatively connected to a power supply and a battery detection circuitry;
a capacitor;
wherein the capacitor is charged by current flowing through the circuit breaker;
a resistor divider network;
wherein the resistor divider network is operatively connected to the ADC;
wherein the resistor divider network is adapted to drop down the capacitor voltage;
wherein user configuration is communicated from the display controller to the first controller so as to adaptively modify functionality of said first controller based on user configuration;
wherein the main controller operatively maintains the capacitor voltage to a desired value;
wherein as the current flowing through the circuit breaker drops to zero suddenly, the capacitor starts discharging and after a period of time, the trip unit loses its power; or
wherein as the current flowing through the circuit breaker fluctuates at lower values, the capacitor voltage is correspondingly varied; and
wherein the voltage at the ADC corresponds to the maximum capacitor voltage operatively enabling the main controller to monitor the ADC voltage and determine the corresponding capacitor voltage by drop-down factor of the resistor divider network.

2. The trip unit as claimed in claim 1, wherein the electronic trip unit is powered by current flowing through the circuit breaker.

3. The trip unit as claimed in claim 1, wherein the first controller is a main controller.

4. The trip unit as claimed in claim 1, wherein the display controller comprises a liquid crystal display and a keypad interface.

5. The trip unit as claimed in claim 1, wherein the first and second data flash module is a non-volatile data storage unit.

6. The trip unit as claimed in claim 1, wherein the second data flash module is adapted to store trip records, event log, energy accumulation, configuration data and the like generated by the first controller.

7. The trip unit as claimed in claim 1, wherein the first controller communicates with the second controller by a communication interface.

8. The trip unit as claimed in claim 4, wherein a user configures the display controller.

9. The trip unit as claimed in claim 4, wherein the user can view on the liquid crystal display, data stored on the second data flash module.

10. The trip unit as claimed in claim 1, wherein the main controller comprises a Pulse Width Modulation (PWM) module that operatively maintains the capacitor voltage.

11. The trip unit as claimed in claim 10, wherein the PWM module maintains the capacitor voltage at a value higher that the voltage required for tripping the circuit breaker.

12. The trip unit as claimed in claim 11, wherein a Flux Shift Device (FSD) triggers the tripping of the circuit breaker.

13. The trip unit as claimed in claim 12, wherein the FSD is a part of the circuit breaker.

14. The trip unit as claimed in claim 1, wherein the capacitor voltage is comparatively very high when compared to voltage of the main controller.

15. The trip unit as claimed in claim 1, wherein the voltage of the main controller is 3.3V.

16. The trip unit as claimed in claim 15, wherein the ADC reference voltage is same as the voltage of the main controller.

17. The trip unit as claimed in claim 1, wherein the maximum capacitor voltage lies within a range of 3.3V.

18. The trip unit as claimed in claim 1, wherein the power supply is a battery of about 6v.

19. A method of detecting power down condition of a circuit breaker and data management during said power down condition, said method comprising the steps of:
monitoring voltage across a capacitor, by a main controller;
determining a probable power down condition by comparing the voltage across the capacitor to threshold_1;
communicating, by the main controller, a data frame to a display controller of a possible power down condition when voltage across the capacitor is below threshold_1;
avoiding initiation of writing in data flash of display controller when voltage across the capacitor is comparatively below threshold_1;
wherein no data frame which may initiate data flash operation in display controller is sent to the display controller during a possible power down condition from main controller;
saving a copy of data to be communicated to the display controller in a memory of the main controller;
ceasing all read/write operations during possible power down condition in main controller thereby
ensuring reliability of thermal overload protection provided by ETU using the power down detection mechanism based on threshold_2; and
monitoring battery voltage in ‘Battery Mode’ of the Display controller for preventing Flash memory write operation in case of low battery condition thus avoiding memory corruption.

20. The method as claimed in claim 1, wherein the main controller communicates with the display controller by a Serial Peripheral Interface.

21. The method as claimed in claim 1, wherein the memory of the main controller is Random Access Memory.

22. The method as claimed in claim 21, wherein during a possible power down condition, communication on SPI from main controller to the display controller is ceased and copy of data is maintained so that when the voltage across the capacitor becomes healthy, data communication can be resumed.

23. The method as claimed in claim 22, wherein ceasing all read/write operations enables the data in data flash of the display controller to remain intact.
, Description:FIELD OF THE INVENTION

[001] The subject matter of the present invention, in general, relates to tripping of circuit breaker, and more particularly, pertains to data management during power down of an electronic trip unit.

BACKGROUND OF INVENTION

[002] A trip unit is the part of a circuit breaker that opens the circuit in the event of a thermal overload, short circuit or ground fault. An open circuit will not conduct electricity because either air, or some other insulator has stopped or broken the flow of current in the loop.

[003] There are two types of trip units, electromechanical (also referred to as thermal magnetic) and electronic. An electromechanical trip unit has moving parts; it combines a current-sensitive electromechanical device with a thermal-sensitive device and the two devices work together to determine when to mechanically open the circuit. An Electronic Trip Unit (ETU) is programmable device that measures current flowing through the circuit breaker and initiates a trip signal when appropriate.

[004] Molded Case Circuit Breakers’ are used to break the current passing through it in case the current goes above a certain threshold value. These ETU provide a variety of protections such as current protection, voltage protection, frequency protection etc. Settings of the various protections offered can be done through rotary switches, dip switches, and display navigation. Circuit breakers provide energy, current, voltage, frequency metering and can also communicate with external world (SCADA, HMI) using protocols such as CAN (Controller Area Network) bus, MODBUS.

[005] A microcontroller based ETU provides all the features indicated hereinabove. They may employ one or more microcontrollers for performing the operations listed hereinabove. For example, one microcontroller (or main controller) may be used to perform breaker critical operations such as fault sensing, giving trip command to the breaker in case of fault, generating trip records, calculating metering data etc., whereas another microcontroller (or user interface controller) may be used for providing user interface such as display navigation. The display navigation may be used to view/change various protection settings, view trip record data, metering data etc. Since, data is generated in one controller; it needs to be communicated to the display controller (or user interface controller) so that user can view various parameters as and when required.

[006] Also, parameters such as protection settings or trip record can be viewed by the user even after power down. So these parameters are generally stored in non-volatile memory such as data flash. When self-power is not available for main controller, settings can still be configured using display controller in ‘Battery Mode’ with the help of a 6V battery available with the display controller.

[007] These ETU’s may be powered either through auxiliary supplies or by the converting the current flowing through the breaker to the required ETU powering voltage. But the current flowing through the breaker can have fluctuations and can lead to the resetting of the ETU if the current goes below a certain threshold.

[008] Normally with the current, certain capacitors are charged that supply the voltage to the ETU in case of power down but only for a very limited time of the order of few milliseconds. As mentioned hereinabove, there can be large amount of data that can be saved in the data flash memory of the controller such as ETU settings, records, energy data etc. in user interface controller.

[009] These data flash writing are event based and generated in main controller and hence need to write the data in data flash of user interface controller can occur any time. The flash memories generally allow the reading and writing of the data from flash memories according to the user defined size of bytes but before writing operation takes place, data flash needs to be erased. Also this erase operation is Block wise (512 bytes/1024 bytes) and hence may consume time of up to 20ms (Erase plus write). If during power down, any of the data flash writing or erasing activity is happening then it may lead to improper charging of capacitors of the data flash which may even corrupt the data flash memory which is completely undesirable.

[0010] The ETU’s when detect fault condition needs to give a trip command. The trip command can be given to a Flux Shift Device (FSD) which will in turn trip the breaker. Usually with the current flowing through the breaker, a capacitor can be charged that can be used to give required energy to the trip FSD. This energy is usually given by ½*CV2 where C is the capacitance and V is the voltage across capacitor. If the capacitor is not charged till “V” potential, FSD will not trip when trip pulse is issued and instead the capacitor will drain out that might even reset the system. Therefore, it is important to detect the capacitor voltage before issuing trip command.

[0011] Thermal data that corresponds to the bus bar temperature also needs to be stored in the data flash memory main controller when power down is detected. This is because of limitation of self-powered trip units that it cannot keep track of cooling of the bus bars after the current is cut off because the trip unit is not active during that time. Thus, when the breaker is switched on, the trip unit loses information of bus bar temperature which can be hazardous in case of overheating of bus bars. So ETU uses the non-volatile memory module to store the information regarding the feeder or the bus bars and its temperature at the time of issuing a trip command or if power down condition is sensed. Next time when the breaker is turned on, ETU retrieves the information back from the non-volatile memory so that it can provide reliable thermal overload protection.

[0012] Reference is made to US 5038246 A, wherein a self-powered ETU monitors its power and gives the trip signal to the solenoid to ensure the sufficient amount energy required for the circuit interruption successfully. It avoids power loss due to inappropriate engagement of the solenoid. The detection of power voltage is achieved by using electronic circuitry that will give logic HIGH if the power is sufficient otherwise will give logic LOW. This digital signal is read by the microcontroller to make the decision. It does not disclose a self-powered electronic trip unit that employs analog-to-digital converter peripheral of a controller to monitor the power-capacitor voltage that is dropped down using a resistor divider network. This enables the controller to monitor the exact voltage levels which further is used to achieve reliable tripping. The ADC based power voltage detection also enables the controller to keep different thresholds for different tasks to be performed. This feature is used to provide reliability in the tasks of writing data in Flash memory. The probable memory corruption in case of power fluctuations or power failure is prevented.

[0013] Reference is also made to US 6839823 B1 wherein methods for storing data in an erasable nonvolatile memory is disclosed. It refers to increasing reliability of data storage using Flash memory in power-sensitive applications specifically for personal communication devices such as cellular phones. The method employs the same non-volatile memory for both code and data storage and furthermore to recover and to determine the reliability of data in the memory device after a power-loss. Focus here is on recovering data lost during a possible power-loss and determining its reliability by adding a lot of memory overheads such as data headers, sequence tables, group tables having various data fields which contain additional information about the data stored in different blocks of Flash memory. The recovery process involves quantifying the degree of reliability of a particular data. This demands availability of large amount of memory compared to the actual data and also processing time for dynamic memory allocation and the data recovery.

[0014] The state of art ETU’s may be powered either through auxiliary supplies or by the converting the current flowing through the breaker to the required ETU powering voltage. But the current flowing through the breaker can have fluctuations and can lead to the resetting of the ETU if the current goes below a certain threshold. As there can be a large amount of data saved in the data flash memory of the controller such as ETU settings, records, energy data etc. in user interface controller. These data flash writing are event based and generated in main controller and hence need to write the data in data flash of user interface controller may occur any time. If during power down, any of the data flash writing or erasing activity is happening then it may lead to improper charging of capacitors of the data flash that may even corrupt the data flash memory, something that is completely undesirable.

[0015] The ETU issues a trip command when a fault is detected. The trip command may be given to a flux shift device (FSD) that will in turn trip the breaker. It is important to detect the capacitor voltage before issuing trip command because the capacitor will provide the required energy to pop the FSD. If capacitor is not charged till required voltage, the energy it will deliver will not be sufficient to drive FSD and hence breaker will not trip. Instead it may lead to complete resetting of ETU.

[0016] Therefore, there is a need to detect, beforehand, any power down condition and specifically detect the voltage across the capacitor, and based on the capacitor voltage allow/block the data flash memory operations in both controllers. To overcome the drawbacks in conventional ETU’s, the present invention discloses a system and method of detecting power down condition in ETU and data flash memory operation during power down of a microcontroller based ETU of a circuit breaker.

SUMMARY OF THE INVENTION

[0017] The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

[0018] An object of the present invention is to provide a self-powered electronic trip unit which is a real-time embedded system with memory and timing constraints.

[0019] Another object of the present invention is to determine the possible power down condition and taking measures to prevent flash memory from getting corrupted.

[0020] Another object of the present invention is to provide a method to beforehand detect power down condition of an electronic trip unit.

[0021] Another object of the present invention is to specifically detect the voltage across a capacitor and based on the capacitor voltage, allowing/blocking data flash memory operations in both main controller and user interface controller.

[0022] Another object of the present invention is to help maintain the electronic trip unit healthiness and increases system reliability.

[0023] Another object of the present invention is to provide a self-powered electronic trip that employs analog-to-digital converter peripheral of a controller to monitor the power-capacitor voltage that is dropped down using a resistor divider network.

[0024] Another object of the present invention is to provide an electronic trip that enables the controller to monitor the exact voltage levels to achieve reliable tripping.

[0025] Another object of the present invention is to enable the controller to keep different thresholds for different tasks to be performed to provide reliability in the tasks of writing data in flash memory thereby avoiding probable memory corruption in case of power fluctuations or power failure.

[0026] Briefly, the present invention pertains to a self-powered electronic trip unit and a method of detecting power down condition. The self-powered electronic trip unit is a real-time embedded system with memory and timing constraints. The method determines the possible power down condition while taking measures to prevent flash memory from getting corrupted. The method detects, beforehand, about any power down condition and specifically detects the voltage across the capacitor, and based on the capacitor voltage, allows/blocks the data flash memory operations in both main controller and user interface controller thereby maintaining the electronic trip units’ healthiness and system reliability.

[0027] A self-powered electronic trip unit for a circuit breaker is disclosed. The self-powered electronic trip unit comprising a first controller operatively connected to a second controller, said first controller further comprising an analog-to-digital converter (ADC) and a first data flash module; wherein the first controller is adapted to sense current and voltage signals, and implementing protection mechanisms; wherein the first controller is adapted to generate trip records, event log, energy accumulation; the said second controller further comprising a second data flash module; wherein the second controller is a display controller; wherein the said second controller is operatively connected to a power supply and a battery detection circuitry; a capacitor; wherein the capacitor is charged by current flowing through the circuit breaker; a resistor divider network; wherein the resistor divider network is operatively connected to the ADC; wherein the resistor divider network is adapted to drop down the capacitor voltage; wherein user configuration is communicated from the display controller to the first controller so as to adaptively modify functionality of said first controller based on user configuration; wherein the main controller operatively maintains the capacitor voltage to a desired value; wherein as the current flowing through the circuit breaker drops to zero suddenly, the capacitor starts discharging and after a period of time, the trip unit loses its power; or wherein as the current flowing through the circuit breaker fluctuates at lower values, the capacitor voltage is correspondingly varied. Hence, the trip unit needs to monitor the capacitor voltage. The healthy capacitor voltage by design is very high for the Main controller which operates on 3.3V which is also its ADC reference voltage. This is why the trip unit has a circuitry which drops down the capacitor voltage using a resistor divider network and it is connected to an ADC channel of the Main controller. It is designed in such a way that the voltage at ADC corresponding to the maximum capacitor voltage lies within the range of 3.3V. This enables the Main controller to monitor the ADC voltage and find the corresponding capacitor voltage using the drop-down factor of the resistor divider network.

A method of detecting power down condition of a circuit breaker and data management during said power down condition is disclosed. The method comprises the steps of: monitoring voltage across a capacitor, by a main controller; determining a probable power down condition by comparing the voltage across the capacitor to threshold_1; communicating, by the main controller, a data frame to a display controller of a possible power down condition when voltage across the capacitor is below threshold_1; avoiding initiation of writing in data flash of display controller when voltage across the capacitor is comparatively below threshold_1; wherein no data frame which may initiate data flash operation in display controller is sent to the display controller during a possible power down condition from main controller; saving a copy of data to be communicated to the display controller in a memory of the main controller; ceasing all read/write operations during possible power down condition in main controller. Ensuring reliability of thermal overload protection provided by ETU using the power down detection mechanism based on threshold_2; and Monitoring battery voltage in ‘Battery Mode’ of the Display controller for preventing Flash memory write operation in case of low battery condition thus avoiding memory corruption.
[0028]
[0029] Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[0030] The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

[0031] Figure 1 illustrates the block diagram of a self-powered electronic trip unit according to one implementation of the present invention.

[0032] Figure 2 illustrates a flowchart of the method of detecting power down condition according to another implementation of the present invention.

[0033] Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0034] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

[0035] Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

[0036] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

[0037] It is to be understood that the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0038] By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0039] Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

[0040] It should be emphasized that the term “comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or component but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0041] The subject invention lies in providing a system and a method of detecting power down condition in an electronic trip unit.

[0042] The present invention pertains a self-powered electronic trip unit and a method of detecting power down condition. The self-powered electronic trip unit is a real-time embedded system with memory and timing constraints. The method determines the possible power down condition while taking measures to prevent flash memory from getting corrupted. The method detects, beforehand, about any power down condition and specifically detects the voltage across the capacitor, and based on the capacitor voltage, allows/blocks the data flash memory operations in both main controller and user interface controller thereby maintaining the electronic trip units’ healthiness and system reliability.

[0043] In one implementation, a self-powered electronic trip unit which is a real-time embedded system with memory and timing constraints is provided for.

[0044] In another implementation, determining the possible power down condition and taking measures to prevent flash memory from getting corrupted is provided for.

[0045] In another implementation, a method to beforehand detect power down condition of an electronic trip unit is provided for.

[0046] In another implementation, specifically detecting the voltage across a capacitor and based on the capacitor voltage, allowing/blocking data flash memory operations in both main controller and user interface controller is provided for.

[0047] In another implementation, maintaining the electronic trip unit healthiness and increasing system reliability is provided for.

[0048] In another implementation, a self-powered electronic trip employing an analog-to-digital converter peripheral of a controller to monitor the power-capacitor voltage dropped down using a resistor divider network is provided for.

[0049] In another implementation, an electronic trip enabling a controller to monitor the exact voltage levels to achieve reliable tripping is provided for.

[0050] In another implementation, the controller maintaining a plurality of thresholds for different tasks to provide reliability to the task of writing data in flash memory to avoid probable memory corruption in case of power fluctuations or power failure is provided for.

[0051] The electronic trip unit is an intelligent module and its primary function is to sense the current flowing through the circuit breaker terminals and giving trip command to the breaker in case of an electrical fault to cut-off the current. The trip unit offers variety of protections for different kind of electrical faults, metering of different parameters, maintaining trip records, event logs, user interface including Liquid Crystal Display (LCD) display and keypad for viewing these parameters or configuring the settings of the trip unit. The architecture of the trip unit consists of two controllers serving different purposes. The main controller is responsible for sensing the current and voltage signals and implementing the protection processes. The second controller is dedicatedly used for the user interface that includes the LCD display and the keypad interface hence the second controller could be referred to as display controller.

[0052] One more important purpose served by the display controller is non-volatile data storage using its flash memory module. The non-volatile data in this system includes trip records, event log, energy accumulation, configuration (settings) data etc. The generation of data such as trip records, event log, and energy accumulation happens in the main controller since it serves the primary function of sensing current and providing protections. This is why the communication interface between the two controllers is a very important aspect of the system which enables the data transfer to achieve the complete functionality. The settings configured by the user using display controller are communicated to the main controller that can modify its functionality based on the updated settings. The main controller sends the generated data to the display controller which saves the required data in its flash storage which can also be viewed by the user on LCD display. When self-power is not available for main controller, settings can still be configured using display controller in ‘Battery Mode’ with the help of a 6V battery available with the display controller.

[0053] Figure 1 illustrates the block diagram of the electronic trip unit that derives its power from the current flowing through the breaker and can have current fluctuations depending on the load. The power from the current is used to charge the power capacitor to a specified value. The main controller board has Pulse Width Modulation (PWM) module that maintains the capacitor voltage at the specified value. This value is higher than the voltage required for providing sufficient energy for the flux shift device (FSD) to trigger the tripping of breaker. If the primary current drops to zero suddenly, the capacitor starts discharging and within a few milliseconds the trip unit loses its power. If the current keeps fluctuating at lower values, then the capacitor voltage also keeps varying. Hence the trip unit has a system to monitor the capacitor voltage. The capacitor voltage is very high when compared to the main controller that operates on 3.3V which is also the Analog-to-Digital Converter (ADC) reference voltage. This is the manner by which the trip unit circuitry drops down the capacitor voltage by employing a resistor divider network and is connected to a ADC channel of the main controller. The trip circuitry is designed in such a way that the voltage at ADC corresponding to the maximum capacitor voltage lies within the range of 3.3V. This enables the main controller to monitor the ADC voltage and find the corresponding capacitor voltage using the drop-down factor of the resistor divider network.

[0054] The main controller continuously samples the drop-down voltage signal with the ADC and maintains the data corresponding to the capacitor voltage as ‘Vsense’. The trip unit uses a timer peripheral to generate 1ms interrupt periodically. In the Interrupt Service Routine (ISR) of the 1ms periodic interrupt the ‘Vsense’ is checked for certain thresholds to check the status of the capacitor voltage and necessary actions are performed if the value crosses a particular threshold.

[0055] The minimum voltage that is sufficient to provide energy to fire the FSD successfully is threshold defined as the ‘VSENSE_HEALTHY_THRESHOLD’. If the Vsense value is above this threshold, the system is considered as healthy. The trip unit allows trip command only if the Vsense is above ‘VSENSE_HEALTHY_THRESHOLD’.

[0056] For detecting power down condition, two thresholds for ‘Vsense’ are defined based on the power-critical processes of the trip unit considering their reliability. The two thresholds are defined as ‘POWER_DOWN_VSENSE_HIGH’ and ‘POWER_DOWN_VSENSE_LOW’ as an upper threshold and lower threshold respectively.

[0057] As explained hereinabove, the main controller generates the data and sends to display controller via Serial Peripheral Interface (SPI) communication that takes time according to the size of the frame to be communicated, typically of the order of 3-6ms. The display controller writes data in its data flash memory that might also include erase of data flash if required. So, the process of sending the data from main controller via SPI, to its writing in the flash memory of display controller constitutes a successful operation. This operation may take up to 20ms including data flash erase. In case of power down, depending upon the load connected and the present capacitor voltage, the capacitor will take some time to discharge till controller reset voltage which is let’s say 2.7V. ‘POWER_DOWN_VSENSE_HIGH’ is that value of capacitor voltage in which data to be stored can be communicated from main controller to display controller via SPI communication and can be written successfully in its data flash after performing memory erase operation. This threshold can be kept variable depending on which data is to be transmitted and stored in flash. For example, the data frame with more number of bytes will take more time for communication and also for writing data in data flash so ‘POWER_DOWN_VSENSE_HIGH’ threshold can be kept high for that particular data.

[0058] If the ‘Vsense’ value drops below the threshold ‘POWER_DOWN_VSENSE_HIGH’, the main controller transmit a data frame to the display controller using SPI communication which indicates that power down condition is detected. SPI communication protocol stands for serial peripheral communication protocol which supports single master and multiple slaves. This protocol in general uses 4 wires (MISO, MOSI, Clock, Slave select). While the present invention predominantly discusses about a single master and a single slave communication, it may be noted that it can be used with multiple slaves as well. The main controller is master and the display controller is the slave.

[0059] So, when power down condition is detected any data that involves data flash read/write operation in display controller will not be communicated via SPI to display controller from main controller because power down may happen. The display controller will continue with any data flash reading/writing in progress but will not initiate any new command to read/write in data flash when power down in. As indicated hereinabove, the ‘POWER_DOWN_VSENSE_HIGH’ is selected such that there is enough time for completion of data flash write with erase if the operation is already in progress.

[0060] In the main controller has the thermal data which corresponds to the bus bar temperature. It needs to be stored in the data flash memory of main controller itself when power down is detected. This data is used by the main controller to keep track of cooling time of bus bars and provide reliable Thermal Overload protection. Since it is stored in flash memory of the main controller itself, it needs no communication that will consume time. The only significant time required in this process is the time taken to write this thermal data in the flash memory. Hence a lower threshold of capacitor voltage is kept for this purpose and is called ‘POWER_DOWN_VSENSE_LOW’. When this voltage is detected, thermal data will be written in the data flash memory of main controller. The threshold ‘POWER_DOWN_VSENSE_LOW’ is defined in such a way that the time taken by the capacitor to discharge from this value till the value at which the trip unit loses its power, is just sufficient for the trip unit to save the thermal data. This maximizes the probability of power-down detection and ensuring the reliability of the process of saving thermal data.

[0061] It is possible that because of current fluctuations, the capacitor voltage dips to ‘POWER_DOWN_VSENSE_HIGH’, but the system regains power and ‘Vsense’ value reaches ‘VSENSE_HEALTHY_THRESHOLD’. For such scenarios, the data that was to be sent to display controller for writing in data flash is stored as pending data in Random Access Memory (RAM) of the main controller. When the healthy voltage is detected, the main controller sends a frame via SPI communication indicating healthy power condition to the display controller. This is followed by the pending data that is to be written in the data flash of the display controller. It also possible that the ‘Vsense’ drops past the threshold ‘POWER_DOWN_VSENSE_LOW’ and regains to the healthy voltage threshold ‘VSENSE_HEALTHY_THRESHOLD’. In this case, along with sending the communication frame to the Display Controller, the Main controller erases the thermal data written earlier. This complete process is illustrated in Figure 2.

[0062] Thus, by incorporating the method of power down detection, reliability of the entire ETU is increased by avoiding the corruption of data flash. This method also ensures reliable detection of power down when thermal data can be written in the data flash of main controller and also issue of trip command only when the capacitor is charged to the healthy voltage value, which avoids the system resetting in case the trip command is given without proper capacitor voltage build-up.

[0063] Apart from the above mechanism in which the capacitor voltage is being sensed in main controller, the present invention also incorporates a monitoring method for battery voltage healthiness in display controller. The battery is important to provide ‘Battery Mode’ where settings can be configured even if main controller does not have power and the new settings can be saved in the flash memory of display controller which will be later communicated to the main controller as and when main controller is turned on with self-power.

[0064] A 6V Lithium-ion battery is used for ‘Battery Mode’ of display controller. The battery voltage is dropped down to the voltage level at which the controller operates using a resistor divider network i.e. 3.3V. The display controller board consists of a circuitry which monitors the battery voltage. The circuitry generates a digital output by comparing the battery voltage with a predefined threshold ‘LOW_BATTERY_THRESHOLD’. If the voltage is above threshold then the output is ‘Logic HIGH’ and if the voltage drops below the threshold then the output is ‘Logic LOW’. This is given to the display Controller as digital input which is sensed every 500ms by the controller in ‘Battery Mode’. If ‘Logic LOW’ is sensed by the display controller while monitoring battery status, it indicates that the Battery is drained. At this point it is possible that the display controller is getting powered on but by the time the user navigates and configures the settings using keypad interface, the battery will drain further and display controller may reset. Thus, this is an unhealthy condition to perform a flash memory write or erase operation that may be initiated by the user for saving new settings. In this case if flash memory write or erase operation is allowed then it may lead to the corruption of memory because of unhealthy power supply.

[0065] Thus, when the display controller detects a ‘Battery Low’ condition, then settings configuration by user is not allowed. For this purpose, a specific indication is also continuously displayed to indicate ‘Battery Low’ to the user and if user still tries to save the settings, an error message is displayed as ‘Settings Not Saved’. This ensures reliability of settings data in flash memory of display controller which is important for desired functionality of the trip unit.

[0066] The method involves detecting the voltage of the capacitor that is charged from the current flowing through the breaker in the main controller and predicting from the capacitor voltage a probable power down condition if the capacitor voltage is below certain predefined threshold let’s say threshold_1.

[0067] The display controller is indicated about the power down condition by sending an serial data, for example SPI frame, from main controller so as to avoid any new data flash writing in the display controller’s data flash memory. Also, the transmission of any data frame on SPI from main controller to the display controller is avoided which may involve data flash operation in display controller and instead a copy of such data is maintained in main controller’s RAM so that when the voltage across the capacitor becomes healthy the data can be communicated. This will ensure that the display controller’s data flash remains intact by avoiding data flash read/write operation during the power down, and also in case the power regains then information not be lost.

[0068] If the capacitor voltage is below threshold_2 then thermal data is written in the data flash memory of the main controller. Threshold_2 is selected lower than threshold_1 such that if the capacitor voltage is lesser than threshold_2 then there is more probability of power down happening and less of current fluctuations. Threshold_2 is selected such that at this threshold there is sufficient time for writing 2 bytes of thermal data in main controller’s data flash.

[0069] If the display controller detects ‘Battery Low’ condition in ‘Battery Mode’ then settings configuration by user is not allowed. For this purpose, a specific indication is also continuously displayed to indicate ‘Battery Low’ to the user and if user still tries to save the settings, an error message is displayed as ‘Settings Not Saved’. This ensures reliability of settings data in Flash memory of Display controller which is important for desired functionality of the trip unit.

[0070] Some of the important advantages of the present invention, considered to be noteworthy are indicated herein below:

a) A reliable method of power down sensing using multi-level thresholds in self-powered electronic trip units;
b) A method to avoid data flash corruption by restricting data flash operations when power down is detected based on threshold_1, hence ensuring reliability of the settings of ETU or energy metering etc. to ensure desired functioning of ETU;
c) Ensuring reliability of thermal overload protection provided by ETU using the power down detection mechanism based on threshold_2; and
d) Monitoring battery voltage in ‘Battery Mode’ of the Display controller for preventing Flash memory write operation in case of low battery condition thus avoiding memory corruption.

[0071] Although a simple, efficient, effective and economic electronic trip unit and a method of detecting power down condition has been described in language specific to structural features/methods indicated, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or components or devices or methods described therein. Rather, the specific features are disclosed as examples of implementations of an electronic trip with data management feature during power down condition.