WO2015169392A1 - A method for providing status information of a channel's health condition in a communications network - Google Patents

A method for providing status information of a channel's health condition in a communications network Download PDF

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Publication number
WO2015169392A1
WO2015169392A1 PCT/EP2014/059556 EP2014059556W WO2015169392A1 WO 2015169392 A1 WO2015169392 A1 WO 2015169392A1 EP 2014059556 W EP2014059556 W EP 2014059556W WO 2015169392 A1 WO2015169392 A1 WO 2015169392A1
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Prior art keywords
channel
impairments
iec
channel impairments
communications network
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PCT/EP2014/059556
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French (fr)
Inventor
Gargi Bag
Johan Palm
Thanikesavan Sivanthi
Linus Thrybom
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Abb Technology Ltd
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Priority to PCT/EP2014/059556 priority Critical patent/WO2015169392A1/en
Publication of WO2015169392A1 publication Critical patent/WO2015169392A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
    • H04L43/0805—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters by checking availability
    • H04L43/0811—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters by checking availability by checking connectivity
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
    • H04L43/0823—Errors, e.g. transmission errors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
    • H04L43/0852—Delays
    • H04L43/0864—Round trip delays
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
    • H04L43/0852—Delays
    • H04L43/087—Jitter
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/08—Monitoring or testing based on specific metrics, e.g. QoS, energy consumption or environmental parameters
    • H04L43/0876—Network utilisation, e.g. volume of load or congestion level
    • H04L43/0888—Throughput
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/10—Active monitoring, e.g. heartbeat, ping or trace-route
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L43/00—Arrangements for monitoring or testing data switching networks
    • H04L43/16—Threshold monitoring
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them

Definitions

  • the present invention relates to the technical field of teleprotection.
  • it concerns a method for providing status information of a communication channel's health condition in a communications network to protection Intelligent Electronic Devices (lEDs) and local control systems.
  • lEDs protection Intelligent Electronic Devices
  • Intelligent Electronic Devices are used for control, protection and monitoring of a power system network.
  • the I ED receives data from sensors and power system equipment, such as circuit breakers, capacitors and transformers and can issue control commands, such as tripping commands for opening e.g. circuit breakers, tap changers or contact switches if they detect voltage, current, or frequency anomalies, or can effectuate a close command for closing a circuit breaker or raising/lowering voltage levels in order to maintain a desired level.
  • sensors and power system equipment such as circuit breakers, capacitors and transformers and can issue control commands, such as tripping commands for opening e.g. circuit breakers, tap changers or contact switches if they detect voltage, current, or frequency anomalies, or can effectuate a close command for closing a circuit breaker or raising/lowering voltage levels in order to maintain a desired level.
  • IEC 61850 is a standard for the design of electrical substation automation.
  • the IEC 61850 standard is the result of years of work by electric utilities and vendors of electronic equipment to produce standardised network communication systems for power utility automation.
  • protection and control lEDs are designed to support the IEC 61850 standard for substation automation systems.
  • Teleprotection systems have high safety, security, and reliability requirements.
  • Typical examples of teleprotection systems are line differential protection, distance protection and wide area protection and control.
  • the transmission line faults in these systems are cleared using state comparison or analogue comparison protection schemes that rely on the communication channel to convey status and measurements to the lEDs at each end of the transmission line.
  • the communication channel has to be fast and reliable in order to ensure that only the faulty line section is tripped and to allow the other line sections that are not affected by the fault to continue their operation.
  • the WAN communication channel besides physical failures, can have other impairments that can affect the proper functioning of the teleprotection system. Examples of such impairments are drop in channel quality, tampered or malformed messages and late arrival of valid data.
  • IEC 61850 substations The status and measurements in IEC 61850 substations are communicated using Generic Object Oriented Substation Events (GOOSE) and Sampled Value (SV) messages respectively.
  • GOOSE Generic Object Oriented Substation Events
  • SV Sampled Value
  • IEC 61850 comprises health report signalling which indicate either “OK”, “Warning” or “Alarm”, but is not used to signal WAN channel impairments.
  • US 2009254655 discloses a method for mapping network events (packet latency, diagnostics, access attempts etc.) into a format supported by a SCADA system, e.g. IEC 61850.
  • US 2013054784 shows a method for monitoring teleprotection traffic, e.g. using the IEC 61850 protocol.
  • a network device monitors a header inserted in the traffic messages to obtain performance metrics such as packet drops, latency, etc.
  • US 2004010627 discloses that the Ethernet status, e.g. "operating as expected”, “operating, but in an unexpected manner” or “failed” is communicated. The status information is said to be recognisable by common industrial protocols.
  • EP 2530541 A1 shows a supervising system based on IEC 61850 messages, where the communication network load is predicted in advance, based on measured delay.
  • the present invention introduces a method for providing status information of the condition of a channel in a communications network, thereby facilitating the prediction of an impending communication channel failure.
  • the invention is based on the insight that early indicators on the channel status can help protection lEDs to predict the impending channel failure or anomalies and thereby enabling them to adapt their reaction times and/or their reach in the protected transmission line before the channel fails.
  • IEC 61850 describes the logical node class "ITPC" that comprises data relevant to supervision and setting of teleprotection communication channels.
  • the data object "EEHealth” is used to indicate the state of the communication channel.
  • the channel can be in one of the states “OK”, “Warning” and “Alarm”.
  • the mechanism for detecting WAN channel impairments and their subsequent mapping to the attributes in the IEC 61850 health report information model is not discussed as it is outside the scope of the standard.
  • a method for providing status information of a channel's health condition in a communications network is provided as defined in claim 1 .
  • the status information of a channel's health condition in a communications network is provided by the mechanism of predicting channel failures by detecting impending channel impairments and mapping the detected channel impairments to attributes in the IEC 61850 health report information model.
  • the detected channel impairments are reported to protection lEDs and/or local Supervisory Control And Data Acquisition (SCADA), through in-band signalling, which then enables the protection lEDs and/or local SCADA to take proactive actions, such as adapting their reaction times and/or their reach in the protected transmission line.
  • the in-band signalling avoids using dedicated messages for providing information on channel impairments to protection lEDs and local SCADA.
  • the channel impairments information is piggybacked into the channel supervision messages using the in-band signalling feature. The benefit of such an approach is that it reduces the load on the communication network. Furthermore, it also reduces the processing load on protection lEDs and local SCADA as they do not have to deal with different messages for deducing the channel impairments.
  • Another advantage with the concept of the present invention is that it can help to prevent unnecessary over tripping/clearing by notifying the protection lEDs and SCADA in advance about an impending impairment so that they can adapt their reaction times and/or their reach before the channel failure really happens.
  • Figure 1 shows building blocks which exemplifies the network communication channel health reporting.
  • Figure 2 shows a state diagram in accordance with an example of the present invention.
  • the mechanism for reporting the communication channel impairments to protection lEDs and local SCADA can be realised using the building blocks shown in Error! Reference source not found.. These building blocks are: 10) the communication block which provides network TX and RX interfaces, 1 1 ) the authentication block which maintains the authenticity of data in the network, 12) the channel supervision block which monitors the channel and its frame losses, delay and jitter and 13) the health reporting block, including the IEC 61850 health report information model, that reports information on channel impairments to protection lEDs and local SCADA.
  • the communication block (10) besides providing network TX and RX interfaces, also maintains information such as FCS errors (i.e. corrupted data detected through bad CRC) and utilisation (e.g. buffer overrun or throughput compared to maximum possible). The number of such impairments is compared to a given acceptable lower and upper threshold.
  • the communication block (10) generates events that are sent to the health reporting block (13) whenever the lower or upper threshold is crossed in either direction (i.e. upwards and downwards).
  • the authentication block (1 1 ) provides the mechanism for detecting authentication failures on a network communication channel.
  • the authentication mechanism uses an authentication checksum and a monotonically increasing sequence number per channel. This mechanism is used to detect
  • the authentication block (1 1 ) compares the number of such impairments with a given lower and upper threshold and generates events that are sent to the health reporting (13) block whenever the accepted lower or upper threshold is crossed in either direction.
  • the channel supervision block (12) provides the mechanism for monitoring a point-to- point communication channel. This is accomplished by each end-point, in a given communication channel, using keep-alive messages. Each end-point sends these messages regularly, with a time interval that is known to both end-points. In case redundancy is used, these keep alive-messages are also sent on the redundant links. Furthermore, each end-point, on a given communication channel, expects to receive the keep-alive message regularly and if one does not arrive within a given maximum timeout interval (that is typically a predefined multiple of the keep-alive message interval) the channel is assumed to have failed.
  • a given maximum timeout interval that is typically a predefined multiple of the keep-alive message interval
  • the mechanism In addition to detection of channel failures, the mechanism also monitors round-trip time (RTT) and variations of RTT (i.e. jitter). This is accomplished by regularly sending a RTT request message that has a time interval which is a multiple of the keep-alive message interval (e.g. every x:th keep-alive message is a RTT request message). An end-point will interpret the reception of such an RTT request the same way it interprets a regular keep- alive message. The receiver responds to every received RTT request with an RTT response message. The timestamps (provided by the end-points) within the RTT request and response messages are used to determine the channel round-trip time. The channel supervision mechanism also keeps track of variation in the RTT for a communication channel.
  • RTT round-trip time
  • jitter variations of RTT
  • the channel supervision block (12) generates events to the health reporting block (13) whenever a keep-alive message is received within the keep-alive message interval or if it is not received within a given timeout interval or whenever the RTT delay/jitter crosses the accepted lower or upper threshold.
  • FIG. 2 An embodiment for providing status information of a channel's health condition in a communications network is shown in Figure 2.
  • the communication channel can be modelled using the IEC 61850 health report information model, i.e. the ITPC logic node instance including its data and data attributes.
  • FCS frame check sequence
  • CRC bad cyclic redundancy check
  • packet losses tampered or malformed messages that are transmitted deliberately (man in the middle or replay attack) or inadvertently (wrong configuration) to the substation edge devices and late arrival of valid data (that is of no use as an over trip has already happened).
  • the data object "EEHealth" in the IEC 61850 health report information model indicates the state of the communication channel via the "stVal" data attribute.
  • This data attribute can take one of the enumeration values "OK” (20), “Warning” (21 ) and “Alarm” (22).
  • the quality of the information provided in the "stVal” attribute is conveyed by the "q" data attribute within the "EEHealth” data object.
  • the status information of the channel's health condition is provided by detecting one or a plurality of channel impairments and mapping the detected one or a plurality of channel impairments to the data attributes in the IEC 61850 health report information model .
  • the channel impairments can be conveyed in the IEC 61850 health report information model from an IED by exploiting the "validity", "detailQual” and "source” attributes of "q".
  • the state diagram in Figure 2 shows the different “stVal” states corresponding to the channel health condition.
  • the validity of information "EEHealth.stVal” can be either "good” or "questionable”.
  • a value equal to "good” implies that the IED is certain about the information provided in the "stVal”
  • the value "questionable” implies that there is an abnormal channel condition that is observed by the IED and it is up to the protection lEDs and local SCADA to decide on what to do with the data.
  • the actual abnormal condition is conveyed to the protection lEDs and local SCADA in the "detailQual" attribute.
  • a value equal to "oscillatory" in the "detailQual” attribute implies that a certain channel impairment observed in a given sliding time window is in between a lower threshold and an upper threshold. Examples of such impairments are sporadic packet losses, jitters and FCS errors.
  • a value equal to "inconsistent” in the “detailQual” attribute implies that the channel is still receiving frames but they are tampered or malformed messages (authentication failures) and the number of such received messages is above a certain lower threshold. An oscillating or inconsistent channel will move from the "OK” state (20) to the "Warning" state (21 ). If the impairments are recurrent and are above the upper threshold then it will move to the "Alarm” (22) state.
  • An example of a lower threshold value for frame losses is 2 frames per second and an example of a higher threshold value for frame losses is 10 frames per second.
  • an example of a lower threshold value is 1 ms and an example of a higher threshold value is 5 ms.
  • the "Warning" (21 )/" Alarm” (22) state may need to be kept for some time, in order for other systems to react.
  • an exemplifying scenario for frame losses can be: If the frame loss is 0 per second, then the channel state is "OK" (20). If the frame loss is greater than or equal to 1 per second, then the state is "Warning” (21 ), and if the frame loss is greater than or equal to 5 per second, then the state is "Alarm” (22).
  • the transient checks do not apply to keep-alive messages that need a special treatment.
  • the IED does not receive a keep-alive message then it will set the "detailQual" attribute to "oldData” and move from the "OK" state (20) to the "Warning” state (21 ).
  • the channel will move from the "Warning" state (21 ) to the "Alarm” state (22).
  • the channel will move from the "Alarm” state (22) to the "OK” state (20) only when the impairments are below the lower threshold or when the IED starts to receive the keep- alive message within the maximum timeout interval.
  • the "source” attribute within the quality attribute can be either “process” or "substituted”. The source value is “substituted” in all messages that have "validity" equal to "questionable”.
  • the detected one or plurality of channel impairments are reported to the IED and/or a control system, e.g. a local SCADA, through in-band signalling, such that the IED and/or control system can interpret the one or plurality of channel impairments and take proactive actions which prevents unnecessary over tripping/clearing.
  • a control system e.g. a local SCADA
  • in-band signalling the load on the communication network is reduced as the channel impairment information is piggybacked into the channel supervision messages.
  • a further benefit is that the processing load on the protection lEDs and the local control systems is reduced as using dedicated messages for providing information on channel impairments to protection lEDs and control systems is avoided.
  • the present invention thereby enables faster reaction times and better tripping decisions than traditional teleprotection schemes.

Abstract

This invention concerns a method for providing status information of a channel's health condition in a communications network, the communications network including an IEC 61850 health report information model, the method including detecting channel impairments,mapping the detected channel impairments to the attributes in the IEC 61850 health report information model and reporting the channel impairments to protection IEDs and/or local SCADA in IEC 61850 based substations. The solution proposed helps the protection IEDs to predict an impending channel failure and to adapt their reaction times or their reach of the protected transmission line. This can prevent unnecessary over tripping on external transmission line faults..

Description

A method for providing status information of a channel's health condition in a communications network
TECHNICAL FIELD
The present invention relates to the technical field of teleprotection. In particular, it concerns a method for providing status information of a communication channel's health condition in a communications network to protection Intelligent Electronic Devices (lEDs) and local control systems. BACKGROUND
Intelligent Electronic Devices (lEDs) are used for control, protection and monitoring of a power system network. The I ED receives data from sensors and power system equipment, such as circuit breakers, capacitors and transformers and can issue control commands, such as tripping commands for opening e.g. circuit breakers, tap changers or contact switches if they detect voltage, current, or frequency anomalies, or can effectuate a close command for closing a circuit breaker or raising/lowering voltage levels in order to maintain a desired level.
IEC 61850 is a standard for the design of electrical substation automation. The IEC 61850 standard is the result of years of work by electric utilities and vendors of electronic equipment to produce standardised network communication systems for power utility automation. Nowadays protection and control lEDs are designed to support the IEC 61850 standard for substation automation systems.
Teleprotection systems have high safety, security, and reliability requirements. Typical examples of teleprotection systems are line differential protection, distance protection and wide area protection and control. The transmission line faults in these systems are cleared using state comparison or analogue comparison protection schemes that rely on the communication channel to convey status and measurements to the lEDs at each end of the transmission line. The communication channel has to be fast and reliable in order to ensure that only the faulty line section is tripped and to allow the other line sections that are not affected by the fault to continue their operation. The WAN communication channel, besides physical failures, can have other impairments that can affect the proper functioning of the teleprotection system. Examples of such impairments are drop in channel quality, tampered or malformed messages and late arrival of valid data.
The status and measurements in IEC 61850 substations are communicated using Generic Object Oriented Substation Events (GOOSE) and Sampled Value (SV) messages respectively. Currently, there is an increasing need for exchange of GOOSE and SV messages that carry protection and/or control data over a wide area network (WAN). This IEC 61850 based information exchange among substations for teleprotection and control is highly dependent on the reliability, timeliness, security and integrity of the WAN communication channel.
Presently, IEC 61850 comprises health report signalling which indicate either "OK", "Warning" or "Alarm", but is not used to signal WAN channel impairments.
US 2009254655 discloses a method for mapping network events (packet latency, diagnostics, access attempts etc.) into a format supported by a SCADA system, e.g. IEC 61850.
US 2013054784 shows a method for monitoring teleprotection traffic, e.g. using the IEC 61850 protocol. A network device monitors a header inserted in the traffic messages to obtain performance metrics such as packet drops, latency, etc. US 2004010627 discloses that the Ethernet status, e.g. "operating as expected", "operating, but in an unexpected manner" or "failed" is communicated. The status information is said to be recognisable by common industrial protocols.
EP 2530541 A1 shows a supervising system based on IEC 61850 messages, where the communication network load is predicted in advance, based on measured delay. J. Wang and Z. Wang; "DGMM based Network Traffic Prediction for Smart Substation"; Applied Mechanics and Materials Vol. 339 (2013) pages 401 -408; (2013) Trans Tech Publications, Switzerland; doi:10.4028/www.scientific.net/AMM.339.401 ; describes a method for predicting IEC 61850 network traffic in a smart substation network. The method can be used to predict and issue pre-warnings of network failures etc.
In US 2012249286, future faults, such as cyber security events in a utility network, are predicted based on the quality of communications. None of the cited documents disclose that the IEC 61850 health report information model should be used to indicate the impairments of the communication channel to the protection lEDs, such that the lEDs can adapt their reaction times and/or their reach in the protected transmission line before the channel fails. SUMMARY
It is an object of the present invention to provide an improved alternative to the above techniques and prior art. More specifically, the present invention introduces a method for providing status information of the condition of a channel in a communications network, thereby facilitating the prediction of an impending communication channel failure.
To achieve these and other objects, a method in accordance with the independent claim is provided.
The invention is based on the insight that early indicators on the channel status can help protection lEDs to predict the impending channel failure or anomalies and thereby enabling them to adapt their reaction times and/or their reach in the protected transmission line before the channel fails.
IEC 61850 describes the logical node class "ITPC" that comprises data relevant to supervision and setting of teleprotection communication channels. The data object "EEHealth" is used to indicate the state of the communication channel. The channel can be in one of the states "OK", "Warning" and "Alarm". However, the mechanism for detecting WAN channel impairments and their subsequent mapping to the attributes in the IEC 61850 health report information model is not discussed as it is outside the scope of the standard. According to a first aspect of the invention, a method for providing status information of a channel's health condition in a communications network is provided as defined in claim 1 .
In accordance with an embodiment of the invention, the status information of a channel's health condition in a communications network is provided by the mechanism of predicting channel failures by detecting impending channel impairments and mapping the detected channel impairments to attributes in the IEC 61850 health report information model. The detected channel impairments are reported to protection lEDs and/or local Supervisory Control And Data Acquisition (SCADA), through in-band signalling, which then enables the protection lEDs and/or local SCADA to take proactive actions, such as adapting their reaction times and/or their reach in the protected transmission line. The in-band signalling avoids using dedicated messages for providing information on channel impairments to protection lEDs and local SCADA. The channel impairments information is piggybacked into the channel supervision messages using the in-band signalling feature. The benefit of such an approach is that it reduces the load on the communication network. Furthermore, it also reduces the processing load on protection lEDs and local SCADA as they do not have to deal with different messages for deducing the channel impairments.
Another advantage with the concept of the present invention is that it can help to prevent unnecessary over tripping/clearing by notifying the protection lEDs and SCADA in advance about an impending impairment so that they can adapt their reaction times and/or their reach before the channel failure really happens.
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages of the present invention will emerge more clearly to a person skilled in the art from the following non-limited detailed description when considered in connection with the attached drawing, wherein: Figure 1 shows building blocks which exemplifies the network communication channel health reporting.
Figure 2 shows a state diagram in accordance with an example of the present invention.
DETAILED DESCRIPTION
The mechanism for reporting the communication channel impairments to protection lEDs and local SCADA can be realised using the building blocks shown in Error! Reference source not found.. These building blocks are: 10) the communication block which provides network TX and RX interfaces, 1 1 ) the authentication block which maintains the authenticity of data in the network, 12) the channel supervision block which monitors the channel and its frame losses, delay and jitter and 13) the health reporting block, including the IEC 61850 health report information model, that reports information on channel impairments to protection lEDs and local SCADA.
Communication block
The communication block (10), besides providing network TX and RX interfaces, also maintains information such as FCS errors (i.e. corrupted data detected through bad CRC) and utilisation (e.g. buffer overrun or throughput compared to maximum possible). The number of such impairments is compared to a given acceptable lower and upper threshold. The communication block (10) generates events that are sent to the health reporting block (13) whenever the lower or upper threshold is crossed in either direction (i.e. upwards and downwards). Authentication block
The authentication block (1 1 ) provides the mechanism for detecting authentication failures on a network communication channel. The authentication mechanism uses an authentication checksum and a monotonically increasing sequence number per channel. This mechanism is used to detect
· Failed (bad) authentication checksum that indicates unauthorized manipulation of data. • If the sequence number is lower than the expected sequence number, which is an indication of a replay attack.
• If the sequence number is higher than the expected sequence number, which is an indication of frame loss.
The authentication block (1 1 ) compares the number of such impairments with a given lower and upper threshold and generates events that are sent to the health reporting (13) block whenever the accepted lower or upper threshold is crossed in either direction. Channel supervision block
The channel supervision block (12) provides the mechanism for monitoring a point-to- point communication channel. This is accomplished by each end-point, in a given communication channel, using keep-alive messages. Each end-point sends these messages regularly, with a time interval that is known to both end-points. In case redundancy is used, these keep alive-messages are also sent on the redundant links. Furthermore, each end-point, on a given communication channel, expects to receive the keep-alive message regularly and if one does not arrive within a given maximum timeout interval (that is typically a predefined multiple of the keep-alive message interval) the channel is assumed to have failed.
In addition to detection of channel failures, the mechanism also monitors round-trip time (RTT) and variations of RTT (i.e. jitter). This is accomplished by regularly sending a RTT request message that has a time interval which is a multiple of the keep-alive message interval (e.g. every x:th keep-alive message is a RTT request message). An end-point will interpret the reception of such an RTT request the same way it interprets a regular keep- alive message. The receiver responds to every received RTT request with an RTT response message. The timestamps (provided by the end-points) within the RTT request and response messages are used to determine the channel round-trip time. The channel supervision mechanism also keeps track of variation in the RTT for a communication channel. The channel supervision block (12) generates events to the health reporting block (13) whenever a keep-alive message is received within the keep-alive message interval or if it is not received within a given timeout interval or whenever the RTT delay/jitter crosses the accepted lower or upper threshold.
An embodiment for providing status information of a channel's health condition in a communications network is shown in Figure 2. The communication channel can be modelled using the IEC 61850 health report information model, i.e. the ITPC logic node instance including its data and data attributes.
The communication channel, besides failures, have other impairments that can affect the proper functioning of the teleprotection system. Examples of such impairments are drop in channel quality that can result in frame check sequence (FCS) errors, i.e. corrupted data detected through bad cyclic redundancy check (CRC), or packet losses, tampered or malformed messages that are transmitted deliberately (man in the middle or replay attack) or inadvertently (wrong configuration) to the substation edge devices and late arrival of valid data (that is of no use as an over trip has already happened).
The data object "EEHealth" in the IEC 61850 health report information model indicates the state of the communication channel via the "stVal" data attribute. This data attribute can take one of the enumeration values "OK" (20), "Warning" (21 ) and "Alarm" (22). The quality of the information provided in the "stVal" attribute is conveyed by the "q" data attribute within the "EEHealth" data object. The status information of the channel's health condition is provided by detecting one or a plurality of channel impairments and mapping the detected one or a plurality of channel impairments to the data attributes in the IEC 61850 health report information model . The channel impairments can be conveyed in the IEC 61850 health report information model from an IED by exploiting the "validity", "detailQual" and "source" attributes of "q". The state diagram in Figure 2 shows the different "stVal" states corresponding to the channel health condition. The validity of information "EEHealth.stVal" can be either "good" or "questionable". A value equal to "good" implies that the IED is certain about the information provided in the "stVal", whereas the value "questionable" implies that there is an abnormal channel condition that is observed by the IED and it is up to the protection lEDs and local SCADA to decide on what to do with the data. The actual abnormal condition is conveyed to the protection lEDs and local SCADA in the "detailQual" attribute.
A value equal to "oscillatory" in the "detailQual" attribute implies that a certain channel impairment observed in a given sliding time window is in between a lower threshold and an upper threshold. Examples of such impairments are sporadic packet losses, jitters and FCS errors. A value equal to "inconsistent" in the "detailQual" attribute implies that the channel is still receiving frames but they are tampered or malformed messages (authentication failures) and the number of such received messages is above a certain lower threshold. An oscillating or inconsistent channel will move from the "OK" state (20) to the "Warning" state (21 ). If the impairments are recurrent and are above the upper threshold then it will move to the "Alarm" (22) state.
An example of a lower threshold value for frame losses is 2 frames per second and an example of a higher threshold value for frame losses is 10 frames per second. For jitter, an example of a lower threshold value is 1 ms and an example of a higher threshold value is 5 ms. However, in this case the "Warning" (21 )/" Alarm" (22) state may need to be kept for some time, in order for other systems to react.
Furthermore, an exemplifying scenario for frame losses can be: If the frame loss is 0 per second, then the channel state is "OK" (20). If the frame loss is greater than or equal to 1 per second, then the state is "Warning" (21 ), and if the frame loss is greater than or equal to 5 per second, then the state is "Alarm" (22).
The transient checks do not apply to keep-alive messages that need a special treatment. In case the IED does not receive a keep-alive message then it will set the "detailQual" attribute to "oldData" and move from the "OK" state (20) to the "Warning" state (21 ). In case there is no keep-alive message received within a given maximum timeout interval then the channel will move from the "Warning" state (21 ) to the "Alarm" state (22). The channel will move from the "Alarm" state (22) to the "OK" state (20) only when the impairments are below the lower threshold or when the IED starts to receive the keep- alive message within the maximum timeout interval. The "source" attribute within the quality attribute can be either "process" or "substituted". The source value is "substituted" in all messages that have "validity" equal to "questionable".
The detected one or plurality of channel impairments are reported to the IED and/or a control system, e.g. a local SCADA, through in-band signalling, such that the IED and/or control system can interpret the one or plurality of channel impairments and take proactive actions which prevents unnecessary over tripping/clearing. The gain of the use of in-band signalling in this invention is that the load on the communication network is reduced as the channel impairment information is piggybacked into the channel supervision messages. A further benefit is that the processing load on the protection lEDs and the local control systems is reduced as using dedicated messages for providing information on channel impairments to protection lEDs and control systems is avoided.
The present invention thereby enables faster reaction times and better tripping decisions than traditional teleprotection schemes.
The person skilled in the art realises that the present invention is not in any way restricted to the embodiments described above. On the contrary, several modifications and variations are possible within the scope of the invention as defined in the appended claims.

Claims

1 . A method for providing status information of a channel's health condition in a communications network, the communications network including an IEC 61850 health report information model, an Intelligent Electronic Device, IED, and a control system, wherein the method including:
detecting one or a plurality of channel impairments,
mapping the detected one or a plurality of channel impairments to attributes in the IEC 61850 health report information model, and
reporting the detected one or plurality of channel impairments to the IED and/or the control system through in-band signalling, thereby enabling the IED and/or control system to predict an impending channel failure.
2. The method according to claim 1 , wherein detecting the one or a plurality of channel impairments includes observing, in a given sliding time window, if at least one of the one or plurality of channel impairments is in between a lower threshold and an upper threshold.
3. The method according to claim 1 , wherein detecting the one or a plurality of channel impairments includes observing, in a given sliding time window, if at least one of the one or plurality of channel impairments is above an upper threshold, and wherein the one or a plurality of channel impairments are lost, delayed, tampered or malformed messages.
4. The method according to any preceding claim, wherein detecting the one or a plurality of channel impairments includes observing if at least one channel impairment is occurring, and wherein the at least one channel impairment is included in the group of sporadic packet losses, jitters, FCS errors, authentication failures and late arrival of keep alive messages.
5. The method according to claim 1 , wherein the mapping of the detected one or plurality of channel impairments to attributes in the IEC 61850 health report information model includes indicating which state the channel has and indicating the quality associated to the channel state.
6. The method according to claim 5, wherein the state of the channel can take one of three different enumeration values.
7. The method according to claim 5, wherein the quality associated to the channel state is indicated by exploiting different attributes.
8. The method according to claim 6, wherein the enumeration values are OK, Warning and Alarm.
9. The method according to claim 7, wherein the attributes are validity, detailQual and source.
10. The method according to claim 9, wherein each attribute can take different enumeration values.
1 1 . The method according to claim 10, wherein the attribute validity can take the enumeration values good or questionable, and wherein the attribute detailQual can take the enumeration values oscillatory, inconsistent or oldData, and wherein the attribute source can take the enumeration values process or substituted.
12. The method according to claim 1 , wherein the control system is a Supervisory Control And Data Acquisition, SCADA.
13. The method according to claim 1 wherein the communications network is a wide area network, WAN.
PCT/EP2014/059556 2014-05-09 2014-05-09 A method for providing status information of a channel's health condition in a communications network WO2015169392A1 (en)

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