Time synchronization between IEDs of different substations

Abstract

A mechanism is provided for time-synchronized communication of packets between a first substation (120a) and a second substation (120b) interconnected by a communication channel. Time information associated with a common reference clock (130) is provided to samples obtained within the second substation and sent to the first substation, where time synchronization of the received samples with samples obtained within the first substation is performed by means of the time information and a time difference between the common reference clock and a local reference clock (140a) of the first substation.

Description

Technical Field

[0001] The embodiments presented herein relate to a method for time-synchronized communication in groups between IEDs, intelligent electronic devices (IEDs), computer programs, and computer program products. Background Technology

[0002] Generally, a substation is part of a power generation, transmission, and distribution system. A substation acts as a connection point between different transmission lines in an electrical system and may additionally convert voltage from high to low, or vice versa, or perform any of several other important functions. Between a power plant and a consumer, electricity can flow through several substations at different voltage levels. Substations may include transformers to change voltage levels between high transmission voltages and low distribution voltages, or at the interconnection of two different transmission voltages.

[0003] Generally, substations are unmanned, relying on remote monitoring and control. In this regard, data streams from different sources within the substation, as well as from other substations, can be fed to line differential protection functions configured to make tripping decisions and thus determine whether a circuit breaker trips.

[0004] Traditionally, synchronous communication via SONET (Synchronous Optical Network) or SDH (Synchronous Digital Hierarchy) with symmetrical communication delays is used to transmit packets to and from line differential protection. When using SONET or SDH, the communication link can be used to obtain a common time reference to compare phase values ​​transmitted from different sources, thus enabling line differential protection.

[0005] Modern wide area networks are packet-based and have non-constant transmission delays (e.g., experiencing jitter and asymmetric delays). Therefore, to use other mechanisms, time references for different packets must be provided.

[0006] One mechanism is to use accurate clocks (such as those provided by the Global Positioning System (GPS)) at all sources to achieve a common time reference in the power grid to be protected. A drawback of using GPS-based clocks is that these clocks are sensitive to severe weather conditions and spoofing.

[0007] Another mechanism is to use a wide area network with high-precision time synchronization capabilities (e.g., IEEE 1588; Precision Time Protocol; PTP) and use a single network clock to synchronize the time of packets sent to all sources involved in the line differential protection function. This mechanism works well in conventional substations. However, when combining line differential protection with merging units, each substation must maintain a common time reference not only within the substation but also with other substations.

[0008] Therefore, it is still necessary to improve time synchronization between substations. Summary of the Invention

[0009] The purpose of the embodiments described herein is to provide time-synchronized communication of packets between different substations that does not encounter the aforementioned problems or at least has reduced or mitigated them.

[0010] According to a first aspect, a method for time-synchronized communication of packets between a first substation and a second substation interconnected via a communication channel is proposed. The method is performed at the first substation and includes receiving sample packets from the second substation via the communication channel. These samples are obtained within the second substation and provide time information associated with a common reference clock. The method further includes: receiving a time indication from the common reference clock via the communication channel; and performing time synchronization of the received sample packets with samples obtained within the first substation. Synchronization includes time compensation of the received sample packets using the time information and a first time difference between the common reference clock and the local reference clock of the first substation.

[0011] According to a second aspect, an IED (Interactive Electronic Device) for grouped time synchronization communication between a first substation and a second substation is proposed. The IED includes processing circuitry. The processing circuitry is configured to cause the IED to perform the method according to the first aspect.

[0012] According to the third aspect, a computer program for time-synchronized communication of groups between substations is proposed, the computer program including computer program code that, when run on an IED in a substation, causes the IED to execute the method according to the first aspect.

[0013] According to a fourth aspect, a computer program product is proposed, comprising a computer program according to a third aspect and a computer-readable storage medium storing the computer program thereon. The computer-readable storage medium may be a non-transitory computer-readable storage medium.

[0014] Advantageously, these aspects typically provide efficient time synchronization between different substations, especially between IEDs in different substations.

[0015] Advantageously, these aspects enable the line differential protection function, which operates on samples obtained from different substations, to operate efficiently.

[0016] Advantageously, these aspects are useful when installing line differential applications in existing substations with less precise time synchronization (based on the Simple Network Time Protocol (SNTP), allowing such installations to be completed without upgrading the station clock.

[0017] The association of time information with a common reference clock generally means that the time information includes information that can be obtained directly or indirectly from the common reference clock. Therefore, the time information may, for example, include an indication of the time provided by the common reference clock. Alternatively or additionally, the time information may include the time difference or an indication of such difference between the common reference clock and the local reference clock of the substation that obtained the timestamped sample, as well as an indication of the time of said local reference clock. Further, the time information may include timestamps based on the common reference clock or based on the local reference clock of the first or second substation. Advantageously, the time information includes information that allows the receiving substation to perform time synchronization of the received, preferably timestamped, sample with the sample obtained within the receiving substation.

[0018] Advantageously, these aspects allow different substations, such as the first and second substations, to operate according to their respective local reference clocks, and allow these substations to communicate with each other even when they are out of sync. Therefore, it will be understood that the first and second substations can operate based on both their different local reference clocks and a common reference clock. Since the substations have their own local reference clocks, they do not necessarily have to rely on a common reference clock for operation.

[0019] Sample grouping and time indication from a common reference clock can be transmitted through the same communication channel (e.g., a packet-switched network) that interconnects substations.

[0020] According to an embodiment, time information associated with a common reference clock, such as a timestamp, can be provided to samples obtained within the first substation. Samples carrying this time information can be transmitted to the second substation in packets containing the first sample information via a communication channel, such as a packet-switched network. Packets of samples received from the second substation can be referred to as packets containing the second sample information.

[0021] It will be understood that this method can be executed by processing circuitry of a substation. Examples of such processing circuitry may include a microprocessor-based controller, such as an intelligent electronic device (IED). Therefore, according to an embodiment, the method can be executed by a first intelligent electronic device (IED) of a first substation, while the second substation may include a second IED for communicating with the first IED via a communication channel. Further, the second IED may be configured to determine a second time difference.

[0022] According to an embodiment, a method for packet-based time synchronization communication between a first IED in a first substation and a second IED in a second substation is proposed, as outlined in conjunction with the foregoing aspects. The method includes performing at least one of a first action and a second action. The first action may include determining a first time difference between a local reference clock and a common reference clock of the first substation. The first action may include sending packets of a first sample obtained within the first substation to the second IED via a network interface. The first packet may be timestamped according to the local reference clock of the first substation and includes an indication of the first time difference. The second action may include receiving packets of a second sample obtained within the second substation from the second IED via the network interface. The second packet may be timestamped according to the local reference clock of the second substation and includes an indication of a second time difference determined by the second IED between the local reference clock and the common reference clock of the second substation. The second action may include performing time synchronization of the samples of the second packet with the samples obtained within the first substation by time compensation of the samples of the second packet according to the difference between the first time difference and the second time difference.

[0023] According to an embodiment, each IED may include its own substation interface for communication within its substation and its own network interface for communication with IEDs in other substations via a packet-switched network. Each substation interface may be associated with its own local reference clock, which serves as a time synchronization reference within the substation. The network interface may be configured to receive signals from the common reference clock.

[0024] According to an embodiment, the sample can represent the current value. The differential current can be calculated as the difference between the compensated sample and the sample obtained in the first substation. The differential current can be provided to the line differential protection function in the first substation.

[0025] According to some embodiments, the first time difference can be determined as the difference between a common reference clock and a local reference clock of the first substation. Further, the second time difference can be determined as the difference between the common reference clock and a local reference clock of the second substation. Before providing differential current to the line differential protection function, it can be verified whether the difference between the first and second time differences is less than a time threshold. When the difference between the first and second time differences is not less than the time threshold, the line differential protection function can be prevented. Furthermore, an alarm notification of lost time synchronization communication may be issued.

[0026] According to some embodiments, PTP or TSN can be used to facilitate communication via a network interface. Furthermore, a PTP utility profile can be used to facilitate communication via a substation interface. A PTP telecom profile can be used to facilitate communication via a network interface.

[0027] According to an embodiment, each local reference clock can have higher accuracy than the common reference clock. Alternatively, each local reference clock can have lower accuracy than the common reference clock. Furthermore, each local reference clock can be a substation clock, while the common reference clock can be one of the substation clocks or a network clock.

[0028] Other objectives, features, and advantages of the appended embodiments will become apparent from the following detailed disclosure, from the appended dependent claims, and from the accompanying drawings.

[0029] Generally, unless otherwise expressly defined herein, all terms used in the claims will be interpreted according to their ordinary meaning in the art. Unless otherwise expressly stated, all references to “an / a / the element, device, component, apparatus, module, action, etc.” will be openly interpreted as referring to at least one instance of the said element, device, component, apparatus, module, action, etc. Unless expressly stated otherwise, the actions of any method disclosed herein need not be performed exactly in the order disclosed. Attached Figure Description

[0030] The inventive concept will now be described by way of example and with reference to the accompanying drawings, in which:

[0031] Figure 1 This is a schematic diagram illustrating a substation network according to an embodiment;

[0032] Figure 2 A schematic illustration of an embodiment Figure 1 Part of the substation network;

[0033] Figure 3 This is a flowchart of the method according to the embodiment;

[0034] Figure 4 This is a schematic diagram illustrating the functional units of an IED according to an embodiment; and

[0035] Figure 5 An example of a computer program product including a computer-readable storage medium according to an embodiment is shown. Detailed Implementation

[0036] The inventive concept will now be described more fully below with reference to the accompanying drawings, in which certain embodiments of the inventive concept are illustrated. However, the inventive concept can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be exhaustive and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Throughout the specification, similar reference numerals refer to similar elements. Any action or feature illustrated by dashed lines should be considered optional.

[0037] Figure 1 This is a schematic diagram illustrating a substation network 100 to which embodiments proposed herein may be applied. The substation network 100 includes merging units (MUs) 170a:170f that act as data sources. MUs 170a:170f are configured to provide data streams (samples in packets) to line differential protection functions 150a:150c. Each data stream may include, for example, analog samples representing voltage or current measurements of MUs 170a:170f in the substation network 100. MUs 170a:170f belong to substations 120a:120c in the substation network 100 and provide samples to IEDs 200a:200c and 160a:160i.

[0038] Each line differential protection function 150a:150c is part of, integrated with, or co-located with a corresponding IED in IED 200a:200c. In this respect, each IED 200a:200c may itself be a line differential protection function 150a:150c, or the line differential protection function 150a:150c may be implemented in IED 200a:200c. Different examples of line differential protection functions may exist. In some examples, the line differential protection function 150a:150c is a relay protection function or a control function, such as a synchronization check function.

[0039] IEDs 200a and 200c are configured to communicate with each other via a communication channel such as a wide area network (WAN) 110. Although communication between IEDs 200a and 200c is synchronized according to a common reference clock 130, communication within each substation 120a and 120c is synchronized according to its own local reference clock 140a and 140c.

[0040] As mentioned above, time synchronization between substations 120a and 120c still needs to be improved.

[0041] Therefore, at least some of the embodiments disclosed herein are based on using a common reference clock 130 as a common reference for samples associated with line differential protection functions 150a:150c. IED 200a:200c, which houses line differential protection functions 150a:150c, uses its local reference clock 140a:140c to synchronize its own internal clock. As will be further disclosed below, although using only the local reference clock 140a:140c is sufficient to synchronize communications within IED 200a:200c, when transferring samples used by line differential protection functions 150a:150c from one IED 200a:200c to another, both the local reference clock 140a:140c and the common reference clock 130 are required to synchronize the samples used by line differential protection functions 150a:150c or at least those used by line differential protection functions 150a:150c.

[0042] Figure 2 schematically illustrated Figure 1 This is part of a substation network, and the diagram illustrates IED 200a, its interface 180a with the local reference clock 140a, and its interface 180b with the common reference clock 130. Figure 2 As illustrated, IED 200a is internally synchronized with a local reference clock 140a given at time T1 and is configured to calculate the time offset Δ or time difference between the local reference clock 140a and the common reference clock 130 given at time T2. Therefore, Δ = T1 - T2. As will be further disclosed below, this offset Δ can also be used to adjust the timestamps of the time information of samples sent and received in packets to / from IEDs 200b:200c at another substation. This allows time information, such as timestamps, to be provided to all samples using a common timescale, regardless of where the samples are obtained in the substation network 100. Therefore, when IED 200a receives a sample from another IED 200b:200c, it can be adjusted, for example, by resampling, to align the samples before calculating any differential current. This is achieved while keeping communication within substation 120a independent of the common reference clock 130.

[0043] Communication via network interface 180b and communication via substation interface 180a may use different protocols. According to embodiments, Precision Time Protocol (PTP) or Time Sensitive Networking (TSN) is used to facilitate communication via network interface 180b. In some examples, PTP utility profiles (i.e., Precision Time Protocol power utility profiles for frequency synchronization as defined in IEC 61850-9-3) or Precision Time Protocol industrial profiles as defined in IEC 62439-3 are used to facilitate communication via substation interface 180a, while PTP telecommunications profiles (i.e., Precision Time Protocol telecommunications profiles for frequency synchronization) are used to facilitate communication via network interface 180b.

[0044] The relationship between the local reference clocks 140a:140c and the common reference clock 130 can vary. In some respects, each local reference clock 140a:140c has higher accuracy than the common reference clock 130. In other respects, each local reference clock 140a:140c has lower accuracy than the common reference clock 130. The latter may be a case where line differential applications have a lower dependence on substation synchronization. In some examples, each local reference clock 140a:140c is a substation clock. In some examples, the common reference clock 130 is one of the substation clocks 140a:140c or a network clock. That is, in some examples, one of the substation clocks 140a:140c acts as a network clock. This then means that for one of the IEDs, the time difference between its local reference clock and the common reference clock will be zero. Furthermore, the internal clock in one of the IEDs 200a:200c can act as a network clock. Again, this means that for one of the IEDs, the time difference between its local reference clock and the common reference clock will be zero.

[0045] The embodiments disclosed herein particularly relate to a mechanism for time-synchronized packet communication between substations interconnected via a packet-switched network. Specifically, the method can be implemented in conjunction with packet communication between IEDs 200a:200c of the respective substations. These packets may include samples representing current values ​​used by line differential protection functions 150a:150c. Therefore, the implemented time-synchronized communication can be used for efficient time synchronization of the samples used by line differential protection functions 150a:150c, or at least line differential protection functions 150a:150c. To implement such a mechanism, a substation IED 200a, a method executed by the IED 200a, and a computer program product including, for example, code in the form of a computer program, which, when run on the IED 200a, causes the IED 200a to execute the method.

[0046] In the following text, for illustrative purposes and without imposing any limitations, IED 200a will be referred to as the first IED, and IED 200b will be referred to as the second IED 200b. However, this does not imply any hierarchical relationship between the first IED 200a and the second IED 200b. Furthermore, it should be understood that this method can be implemented by means of other processing circuitry within the substation. The IEDs disclosed herein are examples of such processing circuitry and exemplary embodiments illustrating the general concept of time-synchronized group communication between substations as defined in the appended claims.

[0047] Figure 3 This is a flowchart illustrating an embodiment of a method performed at a first substation 120a for performing time-synchronized grouped communication between the first substation 120a and a second substation 120b. In the proposed example, this method can be performed by a first IED 200a at the first substation 120a.

[0048] The first IED 200a of the first substation 120a is configured to perform at least one of a first action and a second action. The first action relates to a scenario where the first IED 200a transmits a first sample packet via a packet-switched network, while the second action relates to a scenario where the first IED 200a receives a second sample packet via the packet-switched network. Therefore, in some aspects, the first IED 200a only transmits sample packets; in other aspects, the first IED 200a only receives sample packets; and in yet another aspect, the first IED 200a both transmits and receives sample packets.

[0049] The first action includes sub-actions S102 and S104:

[0050] S102: The first IED 200a determines a first time difference between the local reference clock 140a and the common reference clock 130 of the first substation 120a. The common reference clock 130 can provide a time indication, for example, via a packet-switched network. This is precisely the definition of the time offset Δ. S104: The first IED 200a sends a packet of a first sample obtained within the first substation 120a to the second IED 200b via network interface 180b and the packet-switched network. Time information is provided to this first packet according to the local reference clock 140a of the first substation 120a. The time information can, for example, include a timestamp based on the local reference clock and an indication of the first time difference. Therefore, the value of Δ can be sent in the first packet. This allows the second IED 200b to determine how much its own local reference clock 140b differs from the local reference clock 140a of the first substation 120a.

[0051] In some respects, it is thus assumed that the first IED 200a sends the sample packets to another substation, for example, including IED 200b:200c.

[0052] The second action includes sub-actions S106 and S108:

[0053] S106: The first IED 200a receives a packet of the second sample obtained within the second substation 120b from the second IED 200b via network interface 180b. Time information is provided to the second packet according to the local reference clock 140b of the second substation 120b. The time information may include, for example, a timestamp based on the local reference clock and an indication of a second time difference determined by the second IED 200b between the local reference clock 140b and the common reference clock 130 of the second substation 120b.

[0054] In some respects, it is thus assumed that the first IED 200a receives packets of samples from other IEDs 200b:200c. The first IED 200a can then use information about the first time difference, as determined in action S102, and an indication of the second time difference to determine how much the local reference clock 140b of the second substation 120b differs from the local reference clock 140a of the first substation 120a. This knowledge is then used to adjust the timestamps of the samples received from the second IED 200b.

[0055] S108: The first IED 200a performs time synchronization of the samples in the second group with the samples obtained in the first substation 120a by performing time compensation on the samples in the second group according to the difference between the first time difference and the second time difference.

[0056] This makes it possible to timestamp all samples using a common time scale, regardless of where the samples were obtained in the substation network 100.

[0057] Therefore, in some embodiments, sub-actions S102 and S104 are executed without sub-actions S106 and S108; in some embodiments, sub-actions S106 and S108 are executed without sub-actions S102 and S104; and in some embodiments, all sub-actions S102, S104, S106, and S108 are executed.

[0058] An embodiment relating to further details of time synchronization communication of packets between substations performed at the first substation 120a will now be disclosed.

[0059] In some aspects, each IED 200a, 200b includes its own substation interface 180a for communication within its substations 120a, 120b, and a network interface 180b for communication with other IEDs 200a, 200b, 200c at other substations 120a, 120b, 120c via a packet-switched network. In some aspects, each substation interface 180a is associated with its own local reference clock 140a, 140b, which serves as a time synchronization reference within the substation. In some aspects, the network interface 180b is associated with a common reference clock 130.

[0060] In a scenario with three or more substations 120a:120c, there can be separate communication links between the different substations, namely, a first communication link between substation 120a and substation 120b, a second communication link between substation 120a and substation 120c, and a third communication link between substation 120b and substation 120c. Each communication link can then have a common reference clock 130, instead of all communication links sharing a single common reference clock. Then, in step S102, the first IED 200a determines a corresponding first time difference between its local reference clock 140a at the first substation 120a and the corresponding common reference clock 130 of all communication links used by the first IED 200a to send and receive packets to / from other IEDs 200b:200c.

[0061] Generally, line differential protection function 150a is based on current (and voltage) measurements at each end of a line or network. Measurements (or sampling of current (and voltage) values) can be performed in IED 200a:200b, MU 170a:170f, or via non-traditional instrumentation transformers (NCITs) and other suitable measuring devices and / or sensors. Therefore, at least two ends are required, but depending on the network topology and the availability of processing equipment, up to five ends may be required. In this disclosure, each end is represented by a substation 120a:120c. The basic operating principle of line differential protection function 150a is to sum all received currents. When there is no fault in the line or network, the sum should be zero (or close to zero, depending on measurement accuracy), but when a fault occurs, the sum will show a non-zero differential current flowing through the fault. In order to calculate this differential current, the samples (or phasors) must be aligned in time before summing; otherwise, there is a risk of erroneous differential currents. Therefore, a common time reference between samples from different sources is necessary for the proper operation of the line differential protection function 150a.

[0062] As described above, the common reference clock 130 serves as a reference for communication between IEDs 200a and 200c, and therefore as a reference for sample exchange. A sample can be a raw sample with a timestamp, or a computed phasor with a timestamp. The time knowledge provided by the common reference clock 130 can be used in various ways, either to compensate for the timestamp on the transmitting side or to provide an offset as additional information along with the raw timestamp. This additional information can then be used at the receiving end to compensate for or resample the received sample to synchronize it with its own sample. Furthermore, this additional information can be used at the transmitting end to compensate for or resample the sample to the common sample time based on the common reference clock 130 before sending the sample to the receiving end.

[0063] In some examples, the sample represents a current value. According to an embodiment, the first IED 200a is then configured to perform action S110:

[0064] S110: The first IED 200a calculates the differential current as the difference between the compensated sample and the sample obtained in the first substation 120a.

[0065] This differential current can then be provided to the line differential protection function 150a. Therefore, according to the embodiment, the first IED 200a is configured to execute action S114:

[0066] S114: The first IED 200a provides differential current to the line differential protection function 150a in the first substation 120a.

[0067] However, in some aspects, the differential current is provided to the line differential protection function 150a only when the first IED 200a has confirmed that the difference between the first time difference and the second time difference is less than a time threshold. That is, according to the embodiment, the first IED 200a is configured to perform action S112:

[0068] S112: The first IED 200a verifies whether the difference between the first time difference and the second time difference is less than the time threshold.

[0069] Action S114 will only proceed if the verification in S112 is successful.

[0070] In some respects, when the difference between the first time difference and the second time difference is not less than a time threshold, the line differential protection function 150a should be prevented. That is, according to the embodiment, the first IED 200a is configured to execute action S116:

[0071] S116: When the difference between the first time difference and the second time difference is not less than the time threshold, the first IED 200a prevents the line differential protection function 150a from receiving differential current.

[0072] Furthermore, if PTP is used, there may be a quality indication of differential accuracy, and this quality indication can be used to selectively prevent the line differential protection function 150a from receiving differential current when the quality indication is below a quality threshold. Relatedly, the quality indicator (i.e., the value of Δ) for the first time difference determined in S102 can also be sent to the second IED 200b, and thus the first IED 200a can receive the corresponding quality indicator for the second time difference determined by the second IED 200b.

[0073] Furthermore, when the difference between the first time difference and the second time difference is not less than a time threshold, an alarm notification of lost time synchronization communication can be issued. That is, according to the embodiment, the first IED 200a is configured to execute action S118:

[0074] S118: When the difference between the first time difference and the second time difference is not less than the time threshold, the first IED 200a issues an alarm notification of lost time synchronization communication.

[0075] Figure 4 The components of the IED 200a of the substation 120a according to an embodiment are schematically illustrated with a number of functional units. A product 510 capable of executing a computer program (e.g., presented as...) is used. Figure 5 The processing circuitry 210 may be provided as any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., in the form of software instructions in the storage medium 230. The processing circuitry 210 may further be provided as at least one application-specific integrated circuit (ASIC) or field-programmable gate array (FPGA).

[0076] Specifically, processing circuitry 210 is configured to cause IED 200a to perform a set of operations or actions as disclosed above at the substation. For example, storage medium 230 may store the set of operations, and processing circuitry 210 may be configured to retrieve the set of operations from storage medium 230 to cause IED 200a to execute the set of operations. The set of operations may be provided as a set of executable instructions.

[0077] Therefore, the processing circuitry 210 is thus arranged to perform the methods disclosed herein. The storage medium 230 may also include a persistent storage device, for example, any one or a combination of magnetic storage, optical storage, solid-state storage, or even remotely mounted storage. The IED 200a may further include a communication interface 220. Thus, the communication interface 220 may include one or more transmitters and receivers, which include analog and digital components.

[0078] Specifically, the communication interface 220 implements a substation interface 180a for communication of the IED 200a within its substation 120a, and implements a network interface 180b for communication of the IED 200a with other IEDs 200b, 200c in other substations 120b, 120c via communication channels such as packet-switched networks.

[0079] The processing circuit 210 controls the general operation of the IED 200a, for example, by sending data and control signals to the communication interface 220 and the storage medium 230, receiving data and reports from the communication interface 220, and obtaining data and instructions from the storage medium 230.

[0080] As disclosed above, the line differential protection function 150a is part of, integrated with, or co-located with the IED 200a. Therefore, in some aspects, the IED 200a further includes the line differential protection function 150a.

[0081] Other components and related functions of IED 200a have been omitted to avoid obscuring the concept presented in this paper.

[0082] Figure 5 An example of a computer program product 510 including a computer-readable storage medium 530 is shown. On this computer-readable storage medium 530, a computer program 520 may be stored, which can cause processing circuitry 210 and entities and devices operatively coupled to said processing circuitry (such as communication interface 220 and storage medium 230) to perform methods according to embodiments disclosed herein. Therefore, computer program 520 and / or computer program product 510 can provide means for performing any of the actions disclosed herein.

[0083] exist Figure 5 In the example, computer program product 510 is illustrated as an optical disc such as a CD (optical disc), DVD (Digital Universal Disc), or Blu-ray disc. Computer program product 510 can also be embodied as a memory such as random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), or electrically erasable programmable read-only memory (EEPROM), and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or flash memory (such as Compact Flash Memory). Therefore, although computer program 520 is schematically shown herein as tracks on the depicted optical disc, computer program 520 can also be stored in any manner suitable for computer program product 510.

[0084] The inventive concept has been generally described above with reference to some embodiments. However, it will be readily understood by those skilled in the art that other embodiments besides those disclosed above are also possible within the scope of the inventive concept as defined by the appended claims.

Claims

1. A method for time-synchronized communication of packets between a first substation (120a) and a second substation (120b) interconnected by a communication channel, wherein, The method is performed at the first substation, and wherein the method comprises: receiving (S106) sample packets from the second substation (120b) over the communication channel, wherein the samples are obtained within the second substation and provide time information associated with a common reference clock (130); receiving a time indication from the common reference clock over the communication channel; and performing (S108) time synchronization of samples in the received sample packets with samples obtained within the first substation (120a) by time compensating the samples in the received sample packets by means of the time information and a first time difference between the common reference clock and a local reference clock of the first substation.

2. The method of claim 1, wherein, The time information comprises timestamps of the samples according to the common reference clock.

3. The method of claim 1, wherein, The time information comprises timestamps of samples according to a local reference clock of the second substation and an indication of a second time difference between the local reference clock of the second substation and the common reference clock.

4. The method of claim 3, wherein, There is a time difference between the common reference clock and the local reference clocks of the first and / or second substation.

5. The method according to any one of claims 1 to 4, further comprising: providing samples obtained within the first substation with time information associated with the common reference clock; and sending (S104) samples in a first sample packet to the second substation over the communication channel; wherein the sample packets received from the second substation are second sample packets.

6. The method of any one of claims 1 to 4, wherein, The method is performed by a first intelligent electronic device, IED, (200a) of the first substation and a second IED (200b) of the second substation, wherein the first and second IEDs (200a, 200b) communicate with each other over the communication channel.

7. The method of claim 6, wherein, Each IED (200a, 200b) comprises a substation interface (180a) of that IED for communication within the substation (120a, 120b) of that IED and a network interface (180b) for communication with IEDs (200a, 200b, 200c) of other substations (120a, 120b, 120c) over the communication channel, wherein each substation interface (180a) is associated with a local reference clock (140a, 140b) of that substation interface serving as a time synchronization reference within the substation, and wherein the network interface (180b) is configured to receive a signal from the common reference clock (130).

8. The method of claim 1, wherein, The samples represent current values, and wherein the method further comprises: calculating (S110) a differential current as a difference between the compensated samples and samples obtained within the first substation (120a); and providing (S114) the differential current to a line differential protection function (150a) in the first substation (120a).

9. The method of claim 8, further comprising: determining the first time difference as a difference between the common reference clock and a local reference clock of the first substation, and determining a second time difference as a difference between the common reference clock and a local reference clock of the second substation; and verifying (SI 12) that a difference between the first time difference and the second time difference is smaller than a time threshold before providing the differential current to the line differential protection function (150a).

10. The method of claim 9, wherein, The method further comprises preventing (SI 16) the line differential protection function (150a) when the difference between the first time difference and the second time difference is not smaller than the time threshold.

11. The method of any one of claims 1 to 4, wherein, Each of the local reference clocks (140a, 140b, 140c) has a higher precision than the common reference clock (130).

12. The method of claim 11, wherein, The common reference clock (130) is one of the substation clocks (140a, 140b, 140c) or a network clock.

13. An intelligent electronic device, IED, (200a) for packetized time synchronization communication between a first substation and a second substation, the IED (200a) comprising processing circuitry (210) configured to cause the IED (200a) to perform the method according to any one of claims 1 to 12.

14. A computer program (520) for packetized time synchronization communication, the computer program (520) comprising computer code which, when run on processing circuitry (210) of an intelligent electronic device, IED, (200a) of a substation, causes the IED (200a) to perform the method according to any one of claims 1 to 12.

15. A computer readable storage medium (530) having stored thereon the computer program according to claim 14.

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