Claims:1. A method performed by at least one protective relay in the power system, selected from one or more protective relay over a peer-to-peer communications network, for logging events in a protective relay without using a real time clock (RTC) in PROFIBUS based communication network, the method comprising:
receiving a time event (TE) telegram from a master device in the power system, the TE telegram includes a current time associated with the master device;
receiving a counter value (CV) telegram from the master device, the CV telegram includes a time difference between the current time transmitted in the TE telegram and an actual time of transmission of the TE telegram, and wherein the CV telegram includes a clock value representing a date and a time in a prescribed format for setting the time for the protective relay;
storing the clock value in a memory of the protective relay;
computing, during an event, a timestamp utilizing the clock value from memory and a current time of the protective relay for logging the event associated information along with an accurate time in the memory.

2. The method as claimed in claim 1 further comprises: determining, before receiving the TE telegram, if time synchronization is enabled in the protective relay.

3. The method as claimed in claim 1 further comprises: initiating a first internal time associated with the protective relay on receipt of the TE telegram.

4. The method as claimed in claim 1 further comprises: setting a time for the protective relay utilizing the current time, the time difference, and the internal time.

5. The method as claimed in claim 1 further comprises: initiating a second internal timer associated with the protective relay on storing the clock value, wherein the timestamp is computed utilizing the clock value from memory and a current time associated with the second internal timer of the protective relay for logging the event associated information in the memory.
6. The method as claimed in claims 1 and 5, wherein computing, during the event, the timestamp further comprises:
retrieving the clock value from the memory and a current time associated with the second internal timer to generate a timestamp;
decoding the timestamp to obtain a value in a pre-defined DD:YY:MM HH:MM:SS format; and
logging the event associated information along with the value in the memory.

7. The method as claimed in claim 5, wherein the at least one slave device is adapted to store a clock value received from the master device to utilize the clock value in the event to build a timestamp for logging the event or trip information with the timestamp in DD:MM:YY HH:MM:SS format.

8. The method as claimed in claim 1, wherein the master device is a programmable logic controller (PLC) or a supervisory control and data acquisition (SCDA).
, Description:TECHNICAL FIELD
[0001] The present disclosure generally relates to relays that provide protective control of power distribution systems. In particular, it pertains to, but not by way of limitation, to a system and method for logging alarm and faults in a protective relay without using real time clock (RTC) in PROFIBUS based communication network.

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] In electrical engineering, a protective relay (also sometimes referred to as Protection relays) is a relay device designed to trip a circuit breaker when a fault is detected. Protective relays are designed to sense faults and provide protective control by operating a circuit breaker to interrupt the fault. Power system faults can start and finish rapidly. A modem protective relay incorporates digital signal processing to analyze fault data by capturing sampled waveforms before and after the protective relay interrupts the power system. To fully analyze the cause and extent of a fault, analysis of fault data at multiple locations on the power system is necessary.
[0004] Conventional systems for monitoring protective relay fault data are primarily master-slave communication systems in which a central control station (master) initiates communications to the protective relays (slaves). In master-slave systems, the master initiates all communications. In a common approach, the master control station cyclically and sequentially monitors each slave device for a change of state. This monitoring process introduces significant delays between the time that the relay reacts to a fault and the control station learns of the fault. The control station can signal other relays to record a waveform, but the ensuing delay is unacceptable in master-slave systems for capturing information at the time of the fault across the system.
[0005] Generally, the protective relays are time based. These protective relays perform tasks, respond to events, perform maintenance, take measurements and generate log entries based on time. To be able to perform these tasks, the device needs to incorporate some type of persistent clock, generally referred to as a real time clock. The real time clock is responsible to provide time information within an acceptable accuracy range. The real time clock includes an oscillator and it is typically powered by a main source of power. For example, in a personal computer, the real time clock is powered by power supply that converts AC power to a suitable power level. However, if the main source of power becomes inoperable, the oscillator may stop working and the real time clock can lose its clock information. As a result, the device operation can degrade and/or fail.
[0006] One technique to account for loss of the main source of power is to provide a backup battery. This battery is configured to supply power to the real time clock in the event that the main source of power is off. The battery permits operation of the oscillator until the main source of power is turned back ON. However, including a battery can be expensive and difficult to include in a device.
[0007] There is therefore need in the art to provide an added feature/mechanism to reduce or avoid dependencies of the protective relays/ devices in the system on the RTC or the oscillators. There is also a need to provide a system and method for logging alarm and faults in the protection relays without using RTC in PROFIBUS based communication network. Furthermore, there is a dire need to avoid dependencies of the protective relays/ devices in the system on the RTC or the oscillators but still keep a track of time and synchronize the system accordingly.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.

SUMMARY
[0013] Aspects of the present disclosure relates, but not by way of limitation, to a system and method for logging alarm and faults in a protective relay without using real time clock (RTC) in PROFIBUS based communication network.
[0014] An aspect of the present disclosure relates to a method performed by at least one protective relay in the power system, selected from one or more protective relay over a peer-to-peer communications network, for logging events in a protective relay without using a real time clock (RTC) in PROFIBUS based communication network. The method includes the steps of: receiving a time event (TE) telegram from a master device in the power system, the TE telegram includes a current time associated with the master device; receiving a counter value (CV) telegram from the master device, the CV telegram includes a time difference between the current time transmitted in the TE telegram and an actual time of transmission of the TE telegram, and wherein the CV telegram includes a clock value representing a date and a time in a prescribed format for setting the time for the protective relay; storing the clock value in a memory of the protective relay; and computing, during an event, a timestamp utilizing the clock value from memory and a current time of the protective relay for logging the event associated information along with an accurate time in the memory.
[0015] In an aspect, the method can further include the step of determining, before receiving the TE telegram, if time synchronization is enabled in the protective relay.
[0016] In an aspect, the method can further include the step of initiating a first internal time associated with the protective relay on receipt of the TE telegram.
[0017] In an aspect, the method can further include the step of setting a time for the protective relay utilizing the current time, the time difference, and the internal time.
[0018] In an aspect, the method can further include the step of initiating a second internal timer associated with the protective relay on storing the clock value, wherein the timestamp is computed utilizing the clock value from memory and a current time associated with the second internal timer of the protective relay for logging the event associated information in the memory.
[0019] In an aspect, the method for computing, during the event, can further include the step of: retrieving the clock value from the memory and a current time associated with the second internal timer to generate a timestamp; decoding the timestamp to obtain a value in a pre-defined DD:YY:MM HH:MM:SS format; and logging the event associated information along with the value in the memory.
[0020] In an aspect, the at least one slave device is adapted to store a clock value received from the master device to utilize the clock value in the event to build a timestamp for logging the event or trip information with the timestamp in DD:MM:YY HH:MM:SS format.
[0021] In an aspect, the master device is a programmable logic controller (PLC) or a supervisory control and data acquisition (SCDA).
[0022] The time synchronization telegrams will be transmitted by the master device at regular interval. Such interval will be set by a user when slave device is configured in the profibus network.
[0023] 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
[0024] 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.
[0025] FIG. 1 illustrates an exemplary clock synchronization mechanism used in Profibus, in accordance with an embodiment of the present disclosure.
[0026] FIG. 2 illustrates an exemplary sequence of telegrams for clock synchronization, in accordance with an embodiment of the present disclosure.
[0027] FIG. 3 illustrates an exemplary format of clock value data which is received in each clock value (CV) telegram, in accordance with an embodiment of the present disclosure.
[0028] FIG. 4 illustrates an exemplary flowchart for process of logging event and trip information with current time, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[0029] The following is a detailed description of embodiments of the disclosure illustrated 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] Time synchronization over Profibus was standardized in July 2001. Although, It is not used widely yet. Protective relays are conventionally provided with an internal real time clock which continuously keeps time within the relay. Each event within the relay can be time tagged to this internal clock. In time synchronization over Profibus, Class3 master provides time synchronization message to each Profibus slave device over profibus network. It is a broadcast message from class3 master over Profibus network. Each Profibus slave device receives this broadcast message, but slave device on which time synchronization is enabled use this message data which is nothing but a clock value for further processing. Thus, a connection to a time standard can provide an exact time pulse to the protective relay and a digital time command by which the protective relay can update its internal time clock.
[0032] The real time clock includes an oscillator and it is typically powered by a main source of power. For example, in a personal computer, the real time clock is powered by power supply that converts AC power to a suitable power level. However, if the main source of power becomes inoperable, the oscillator may stop working and the real time clock can lose its clock information. As a result, the device operation can degrade and/or fail.
[0033] Accordingly, the present disclosure provides a system and a method that facilitate logging of events and faults occurred in the protection relays without using RTC. In an embodiment, the present disclosure provides systems and methods that utilize a non-oscillator technique of determining current time without using RTC.
[0034] Aspects of the present disclosure relates, but not by way of limitation, to a system and method for logging alarm and faults in a protective relay without using real time clock (RTC) in PROFIBUS based communication network.
[0035] An aspect of the present disclosure relates to a method performed by at least one protective relay in the power system, selected from one or more protective relay over a peer-to-peer communications network, for logging events in a protective relay without using a real time clock (RTC) in PROFIBUS based communication network. The method includes the steps of: receiving a time event (TE) telegram from a master device in the power system, the TE telegram includes a current time associated with the master device; receiving a counter value (CV) telegram from the master device, the CV telegram includes a time difference between the current time transmitted in the TE telegram and an actual time of transmission of the TE telegram, and wherein the CV telegram includes a clock value representing a date and a time in a prescribed format for setting the time for the protective relay; storing the clock value in a memory of the protective relay; and computing, during an event, a timestamp utilizing the clock value from memory and a current time of the protective relay for logging the event associated information along with an accurate time in the memory.
[0036] In an aspect, the method can further include the step of determining, before receiving the TE telegram, if time synchronization is enabled in the protective relay.
[0037] In an aspect, the method can further include the step of initiating a first internal time associated with the protective relay on receipt of the TE telegram.
[0038] In an aspect, the method can further include the step of setting a time for the protective relay utilizing the current time, the time difference, and the internal time.
[0039] In an aspect, the method can further include the step of initiating a second internal timer associated with the protective relay on storing the clock value, wherein the timestamp is computed utilizing the clock value from memory and a current time associated with the second internal timer of the protective relay for logging the event associated information in the memory.
[0040] In an aspect, the method for computing, during the event, can further include the step of: retrieving the clock value from the memory and a current time associated with the second internal timer to generate a timestamp; decoding the timestamp to obtain a value in a pre-defined DD:YY:MM HH:MM:SS format; and logging the event associated information along with the value in the memory.
[0041] In an aspect, the at least one slave device is adapted to store a clock value received from the master device to utilize the clock value in the event to build a timestamp for logging the event or trip information with the timestamp in DD:MM:YY HH:MM:SS format.
[0042] In an aspect, the master device is a programmable logic controller (PLC) or a supervisory control and data acquisition (SCDA).
[0043] The time synchronization telegrams will be transmitted by the master device at regular interval. Such interval will be set by a user when slave device is configured in the profibus network.
[0044] FIG. 1 illustrates an exemplary clock synchronization mechanism used in Profibus, in accordance with an embodiment of the present disclosure. In an embodiment, a power system under the protective control of a protection scheme connected over PROFIBUS connection is shown. It would be appreciated that the PROFIBUS (Process Field Bus) is a standard for fieldbus communication in automation technology and was first promoted in 1989 by BMBF (German department of education and research) and then used by Siemens. It would be appreciated that PROFIBUS DP-V2 version is for isochronous mode and data exchange broadcast (slave-to-slave communication).
[0045] In FIG. 1, a plurality of protective relays, such as master class 3 102, and DP-Slave 104-1, DP-Slave 104-2, DP-Slave 104-3, DP-Slave 104-3… DP-Slave 104-N (hereinafter referred to as DP-Slave 104), are operatively connected to provide protective control to a power system (not shown). The protective relays are further operatively connected, via appropriate communications ports, to a peer-to-peer communications network 150.
[0046] The protective relays each can include a microprocessor (not shown) and a Profibus ASIC (not shown), an associated memory (not shown), and a time clock (152-1, 152-2, 152-3, 152-4…… 152-N (hereinafter referred to as 152)). The time clocks of the relays are synchronized by a time standard, which can be operatively connected to the peer-to-peer communications network, or can be operatively connected to each of the relays by other appropriate means. Each protective relay samples power system data at an associated point on the power system, and temporarily holds (e.g., in a buffer associated with the microprocessor) some number of cycles of power system data.
[0047] In operation, the peer-to-peer communications network, as contrasted with a conventional master/slave communications network, uses a protocol which allows each device on the communications network to initiate communications if the network is available (that is, if the communications bus is not already in use). In a conventional master/slave system, only the master can initiate communications, and when a slave device senses a condition in the system, the slave cannot communicate this fact until the master requests information from (polls) the slave device. Examples of peer-to-peer communications systems include a so-called Field Messaging System under the Profibus utilizing Master-Slave communication principle or Ethernet protocol.
[0048] The real time clock includes an oscillator and it is typically powered by a main source of power. For example, in a personal computer, the real time clock is powered by power supply that converts AC power to a suitable power level. However, if the main source of power becomes inoperable, the oscillator may stop working and the real time clock can lose its clock information. As a result, the device operation can degrade and/or fail.
[0049] In an embodiment, according to the present disclosure, when a protection relay 104 is powered up, it receives a parameterization request from a class 3 master 102 which will be providing a time synchronization telegrams to protection relay 104 over a PROFIBUS communication. In the parameterization telegram, the protection relay 104 will receive a parameter block structure for time synchronization parameters such as time synchronization interval from class 3 master 102, which can be a programmable logic controller (PLC). This will enable time synchronization functionality execution on the protection relay over PROFIBUS communication.
[0050] In an embodiment, the protection relay receives a time synchronization telegrams from class 3 master 102 over PROFIBUS communication at configured time synchronization interval. In an implementation, the time sync interval rate can be configured to 1 second, 10 second, 1 min and 10 min.
[0051] FIG. 2 illustrates an exemplary sequence of telegrams for clock synchronization, in accordance with an embodiment of the present disclosure. In an embodiment, the PROFIBUS DP-V2 version clocks in a PROFIBUS network can be synchronized.
[0052] In order to synchronize PROFIBUS DP-V2 version clocks in a PROFIBUS network, a station is defined as the time master 102 that is configured to distribute the time within the PROFIBUS network. This time master can be a master and is designated as a class 3 master.
[0053] In an embodiment, the time master 102 reads a current time of the associated clock and starts an internal timer 152-1. As soon as a time event (TE) telegram is sent with the read time to the slaves 104, the internal timer is stopped. In a subsequent counter value (CV) telegram, the time difference between the read time and the sent time is transmitted to the slave 104 by the master 102.
[0054] For example, as shown in FIG. 2, C1 denotes a send time event and C2 denotes actual time event. C1 and C2 are transmitted to the slave 104 by the master 102.
[0055] In an embodiment, on receipt of the TE telegram, the receiving station/ the slave 104 also starts an internal timer 152 associated with the receiving station/ the slave 104. The value of this internal timer plus the current value from the TE telegram and the correction value from the counter value (CV) telegram give the time to be set.
[0056] For example, if C3 denotes a value of the internal timer 152 associated with the receiving station/ the slave 104, C3 along with C1 and C2 received by the receiving station/ the slave 104 is utilized for synchronizing the time of the receiving station/ the slave 104.
[0057] In an embodiment, CV telegram received from PROFIBUS master 102 can include the clock value which can be 8 byte data. In an exemplary implementation, the clock value is used to represent date and time in the required precision for internal device time. In another exemplary implementation, the clock value is a 63-bit unsigned fixed-point number with the integer part in the first 32 bits and the fraction part in the following 31 bits.
[0058] In an embodiment, the last bit of the 63-bit unsigned fixed-point number serves to indicate an active synchronization and therefore a valid timestamp. FIG. 3 illustrates an exemplary format of clock value data which is received in each clock value (CV) telegram. , in accordance with an embodiment of the present disclosure.
[0059] FIG. 4 illustrates an exemplary flowchart for process of logging event and trip information with current time, in accordance with an embodiment of the present disclosure.
[0060] In an embodiment, to be able to provide time to protection relay, parameters for time synchronization should be enabled for protection relay using parameterization over PROFIBUS. At step 402, a condition is checked parameters for time synchronization to provide time to protection relay is enabled or not.
[0061] At step 404, a clock value data received (TE telegram) or not is checked. If the clock value data received, a timer (Timer 1) will be started to get the current time offset at step 406. Upon sending of the timer 1 value, in a subsequent counter value (CV) telegram, the time difference between the read time and the sent time is transmitted to the slave by the master at step 408. At step 410, the clock values (TE and CV) will be stored in the memory by the application running on the protection relay.
[0062] At step 412 on receipt of the TE telegram, the receiving station/ the slave also starts an internal timer associated with the receiving station/ the slave. The value of this internal timer plus the current value from the TE telegram and the correction value from the counter value (CV) telegram give the time to be set.
[0063] In an exemplary implementation, when any event or trip happens on the protection relay is detected at step 414. Upon detection of the event, at step 416, an application running on the protection relay will be build on the timestamp by using the stored clock value (in step 410) and current value of timer (Timer 2). Then this timestamp will be decoded at step 418 by the application running on the protection relay to get the time in DD:MM:YY HH:MM:SS format and now protection relay will log the event or trip information at step 420 with the computed time in the non-volatile memory of protection relay. Timer 2 will be reset and restarted after receiving new CV telegram from the Class3 Master (Clock Master).
[0064] Although the preferred embodiments have been described, it should be pointed out that changes are possible and attainable without departing from the scope of the present invention.
[0065] 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.
[0066] 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
[0067] The present disclosure provides numerous advantages over known systems, especially those that employ RTC with battery backup to provide real time to relay which in turn uses this time to log the fault/trip events because before evolution of Profibus protocol with time sync provision, it was not possible to get time from master over Profibus network. Therefore, there was a requirement for using RTC with Battery backup on Protection relays to get real time clock value..
[0068] The present disclosure avoids the requirement of the RTC Oscillator in the protection relay and therefore backup battery for RTC can be removed from the product which in turn reduces the final cost of the product.
[0069] The present disclosure provides a system and method that facilitates logging of events and faults occurred in the protection relays without using RTC.
[0070] The present disclosure provides systems and methods include utilizing a non-oscillator technique of determining current time without using RTC.