Claims:1. A method of writing thermal information on non-volatile memory of a self-powered electronic trip unit (ETU), the method comprising steps of;
ascertaining a delta time period (P) for the non-volatile memory;
ascertaining, on occurrence of a power down situation, time T since last memory write operation; and
calculating slack time for each consecutive power down situation, wherein the slack time is amount by which T is more than P, and accumulating the slack time as back-up time B;
wherein a write operation on the non-volatile memory is carried out when sum of T and B is more than P.

2. The method of claim 1, wherein the write operation is skipped if sum of T and B is not more than P.

3. The method of claim 1, wherein accumulation of the slack time as back-up time B is carried out at each memory write operation by updating B as (B+T-P).

4. The method of claim 1, wherein the delta time period P is ascertained based on permissible number of write operations on the non-volatile memory and total expected life of the ETU.

5. The method of claim 1, wherein the time T is ascertained based on a real time clock.

6. The method of claim 1, wherein the non-volatile memory is flash memory. , Description:TECHNICAL FIELD
[0001] The present disclosure generally relates to the field of low voltage power distribution systems. In particular, it pertains to a self-powered electronic tripping unit providing thermal overload protection. More specifically it discloses a methodology for storing trip data in a flash memory.

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] Trip units are meant to provide protection to a motor or a feeder in power distribution system from thermal overload condition. A trip unit senses the current flowing through the terminals of the circuit breaker and keeps track of temperature of wires or bus bars in the feeder through which the current is flowing. If current is higher than the rated current value then the excessive heating can damage the insulation resulting into a serious fire hazard. Therefore the trip unit senses the excess current and trips the breaker which cuts off the current to provide thermal overload protection.
[0004] With advent of electronic trip units (ETU) bimetals that were earlier used in the trip units have been replaced by microcontrollers that simulate the current-temperature relationship of the bimetals. The ETUs derive power from the primary current flowing through the terminals of the circuit breaker and therefore are termed as self-powered trip unit because it does not require any additional source of power for its core operation. Hence when current flowing through breaker is disconnected in cases like breaker trip, breaker switched off etc. the trip unit loses its power supply.
[0005] In view of above loss of power, when the ETUs are tripped or switched off, the self-powered trip units is not active. Therefore, they cannot keep track of cooling of the bus bars after the current is cut off. Hence 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.
[0006] For the above reason prior art references disclose use of a non-volatile memory to store and provide the thermal information to the microprocessor after power supply to the ETU is restored. For example United States Patent no. 4616324 discloses a digital over current tripping arrangement having a microprocessor with a volatile digital memory for the current excitation state and an analog-to-digital converter. The arrangement is further provided with an additional permanent memory for storing the thermal excitation state after the system to be protected has been disconnected.
[0007] United States Patent no. 5418677 discloses an electrical over current circuit incorporating both digital based modeling and analog based modeling of the temperature of an electrical conductor to simulate the conductor temperature during all expected operating conditions including a condition when electrical power is unavailable to the electrical over current circuitry.
[0008] United States Patent no. 5850330 discloses a thermal memory comprising a charging resistor connected in series with a diode and the capacitor between the supply voltage and ground.
[0009] However, there is a need to consider the practical limitations of these memory modules and provide thermal overload protection with high reliability. For example non-volatile memory like flash that can be integrated on chip with the processor or also can be an external peripheral, have a limitation on total number of write operations that can be performed on a memory location. If the number of write operations exceeds the maximum number specified, the memory module can get corrupt. Such a situation can be quite costly and dangerous for the effective implementation of the overall thermal protection. Therefore the electronic trip unit needs to take care of this limitation of the memory.
[0010] There is therefore need in the art to provide a method for carrying out write operations on a memory such as flash in an ETU so that it does not get corrupt during lifetime of the ETU on account of number of write operations exceeding the permissible numbers.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0016] A general object of the present disclosure is to provide are liable self-powered ETU for thermal overload protection for a feeder or a motor.
[0017] An object of the present disclosure is to provide a self-powered ETU with a non-volatile memory to store thermal information when power supply to the ETU is cut off.
[0018] Yet another object of the present disclosure is to provide a methodology for writing on the non-volatile memory of the self-powered ETU so that it does not get corrupt during life time of the ETU.
[0019] Yet another object of the present disclosure is to use delta time period of the non-volatile memory to make sure that number of writings does not exceed the permissible number.
[0020] Still another object of the present disclosure is to use slack time available from tripping of the ETU later than delta time period to ensure that the number of writings does not exceed the permissible number.

SUMMARY
[0021] Aspects of the present disclosure pertain to self-powered electronic trip unit (ETU) for thermal overload protection which uses a non-volatile memory like Flash to store thermal data for use when the power supply is resumed back after trip or shut off.
[0022] In an aspect, the disclosure provides a methodology for writing the thermal data on the flash memory on occurrence of trip conditions so that total number of write operations during lifetime of the ETU does not exceed the permissible number thus ensuring that the flash memory does not get corrupt thereby ensuring reliability of the ETU.
[0023] In an aspect, the disclosure makes use of delta time period (P) of the flash memory which is the minimum time duration between two consecutive memory write operations and is determined based on the permissible number of write operations on the flash memory and the life of the ETU. In an aspect, the disclosure makes use of the fact that the ETU does not trip or put off at regular intervals such as P. While P is calculated considering memory write operations occurring at equal intervals but in practical case, a power down can occur at any point. Therefore, the proposed method keeps track of previous memory write operations and the time intervals between them which is tracked using a Real-time Clock (RTC) module. It is then decided whether memory write operation at next power down event is to be performed or not.
[0024] In an aspect, when the time period between the last memory write operation and the current power down event is more than the P, difference is taken as slack and accumulated as back-up time (B) for subsequent use.
[0025] In another aspect, when the time period between the last memory write operation and the current power down event is less than the P, the difference is made up from B and the write operation is carried out. In an alternate scenario, when the time period between the last memory write operation and the current power down event is less than the P and there is not adequate back-up time to make up the difference, it is decided to skip the write operation. Thus in either scenario, it is ensured that the number of write operations do not exceed the permissible number at that point in the life of the ETU.
[0026] 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
[0027] 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.
[0028] FIG.1 illustrates an exemplary flowchart for the method of carrying out a write operation on flash memory of a self-powered electronic trip unit design in accordance to an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0029] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0030] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0031] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0032] Embodiments of the present disclosure pertain to self-powered electronic trip unit (ETU) for thermal overload protection which uses a non-volatile memory like Flash to store thermal data for use when the power supply is resumed back after trip or shut off. Embodiments of the present disclosure provide a methodology for writing the thermal data on the flash memory on occurrence of trip conditions so that total number of write operations during lifetime of the ETU does not exceed the permissible number thus ensuring that the flash memory does not get corrupt thereby ensuring reliability of the ETU.
[0033] It is to be appreciated that though various embodiments of the present disclosure have been explained with reference to a self-powered electronic trip unit (ETU) for thermal overload protection, the disclosed method can be equally well applied in any other application that uses a flash memory for storing data and where data is to be rewritten at irregular intervals. All such applications are within the scope of the present disclosure. The disclosed method can help to optimize writing operations to ensure reliability of the application by ensuring that number of write operations does not exceed permissible numbers during its lifetime.
[0034] The non-volatile memory like Flash, have a limitation on total number of write operations to be performed on a memory location. If the number of write operations exceeds the maximum number specified, the memory module can get corrupt. Therefore the electronic trip unit needs to take care of this limitation of the memory module. The maximum permitted frequency of write operations is calculated based on the permissible number of write operations on the flash memory and the total life of the electronic unit trip unit. This gives a delta time period (P) which is the minimum time duration between two consecutive memory write operations. However, as can be appreciated, literal implementation of this limitation can hamper basic functionality of thermal overload protection as there may be frequent cases of power down events.
[0035] In an aspect, the disclosure makes use of the fact that the ETU does not trip or put off at regular intervals such as P. While P is calculated considering memory write operations occurring at equal intervals but in practical case, a power down can occur at any point. Therefore, the proposed method keeps track of previous memory write operations and the time intervals between them which is tracked using a Real-time Clock (RTC) module. It is then decided whether memory write operation at next power down event is to be performed or not.
[0036] In an aspect, when the time period between the last memory write operation and the current power down event is more than the P, difference is taken as slack and accumulated as back-up time (B) for subsequent use. On the other hand, when the time period between the last memory write operation and the current power down event is less than the P, the difference is made up from B and the write operation is carried out. In an alternate scenario, when the time period between the last memory write operation and the current power down event is less than the P and there is not adequate back-up time to make up the difference, it is decided to skip the write operation. Thus in either scenario, it is ensured that the number of write operations do not exceed the permissible numbers at that point in the life of the ETU.
[0037] Referring now to FIG.1 which illustrates an exemplary flowchart 100 for the disclosed method for carrying out a write operation on flash memory. As shown the ETU at 102 carries out its main function of detecting thermal overload by sensing the current flowing through it and on sensing a thermal overload condition may give a trip signal to cut off power supply to connected load. The time that has elapsed since occurrence of last write operation can be ascertained based on real time clock 104. On detection of a power down condition (referred to as current/present power down situation) at step 106, the time T between the present power down and last write operation can be ascertained and added to previously held value of the back-up time B. This shall amount to making up any shortfall of T by back-up time B.
[0038] In an embodiment, a check can be made as shown at step 108, if the summed value (B+T) is greater than the delta time period P. If so, at step 110, B can be updated by deducting P from (B+T) i.e. Bcurrent = (Bprevious + T) – P. Bcurrent can now replace the previously held value of B. As can be appreciated [(Bprevious + T) – P] is the accumulated slack after the current/present power down and is being stored for future use.
[0039] In an embodiment, when the summed value (B+T) is greater than the delta time period P, at step 112, memory write operation can be carried out to store the thermal information at the time of power down.
[0040] In an embodiment, when at step 108 it is found that of value (B+T) is not greater than the delta time period P, no memory write operation and updation of B shall be done. It is to be appreciated that (B+T) not being greater than P implies a situation where T is less than P and further, available back-up time is not enough to make up short fall in T compared to P.
[0041] Alternatively put, the method of the present disclosure for writing thermal information on non-volatile memory of a self-powered electronic trip unit (ETU) comprises steps of (a) ascertaining a delta time period (P) for the non-volatile memory; (b) ascertaining, on occurrence of a power down situation, time T since last memory write operation; and (c)calculating slack time for each consecutive power down situation, wherein the slack time is amount by which T is more than P, and accumulating the slack time as back-up time B; wherein a write operation on the non-volatile memory is carried out when sum of T and B is more than P.
[0042] In an embodiment, the disclosed method further provides for skipping the write operation if sum of T and B is not more than P.
[0043] In an embodiment, the disclosed method further provides for accumulation of the slack time as back-up time B at each memory write operation by updating B as (B+T-P).
[0044] In an embodiment, the disclosed method further provides for ascertaining the delta time period P based on permissible number of write operations on the non-volatile memory and total expected life of the ETU.
[0045] In an embodiment, the disclosed method further provides for ascertaining the time T based on a real time clock.
[0046] In an embodiment, the non-volatile memory can be a flash memory.
[0047] 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
[0048] The present disclosure provides a reliable self-powered ETU for thermal overload protection for a feeder or a motor.
[0049] The present disclosure provides a self-powered ETU with a non-volatile memory to store thermal information when power supply to the ETU is cut off.
[0050] The present disclosure provides a methodology for writing on the non-volatile memory of the self-powered ETU so that it does not get corrupt during life time of the ETU.
[0051] The present disclosure uses delta time period of the non-volatile memory to make sure that number of writings does not exceed the permissible number.
[0052] The present disclosure uses slack time available from tripping of the ETU later than delta time period to ensure that the number of writings does not exceed the permissible number.