Methodology & Tools for Performance Evaluation of IEC 61850 GOOSE based Protection Schemes Ikbal Ali1, Senior Member, IEEE, Mini S. Thomas2, Senior Member, IEEE, and Sunil Gupta2* Department of Electrical Engineering FET, Jamia Millia Islamia New Delhi, India 1
[email protected],
[email protected], 2*
[email protected] Abstract—IEC 61850 based high speed peer-to-peer communication called GOOSE (Generic Object Oriented Substation Event) has an impact on the development and testing of IEC 61850 relays and the associated protection schemes in modern power system. GOOSE not only provides an opportunity to optimize the system performance at reduced hardware cost but also eliminates various constraints in traditional protection schemes. Performance testing for GOOSE is an important item for the correctness and the real time performance of substation applications. The primary objective of this paper is to analyze the factors affecting the performance of GOOSE based protection schemes. The paper then discusses the methodology and advanced hardware and software tools available for performance measurement of IEC 61850 GOOSE. Keywords—Substation Automation System (SAS); Power System Protection; Switched Ethernet; IEC 61850; GOOSE
I.
INTRODUCTION
In modern power system, traditional microprocessor based relays are now being replaced by Intelligent Electronic Devices (IEDs) that can integrate a variety of protection, control, monitoring and recording functions of power system. The performance of these IEDs governs the reliability and quality of the power system operations. To realize substation automation functions, these IEDs need to be integrated together through a fast and reliable communication network. Modern Substation Automation System (SAS) uses a new high speed Switched Ethernet based international communication standard, IEC 61850, for the development of real time applications of power system. The communication standard IEC 61850, Communication Networks and Systems in Substation, was introduced primarily to gain interoperability between the IEDs from different vendors and lower integration costs [1]. Thus an open system approach in substation automation system can permit the design and development of revolutionary substation automation applications and also bring other benefits like increased speed, reliability and availability with easier extension and up gradation of system over time [2]. IEC 61850 defines data models and the abstract communication services that are mapped over standard communication protocols and hardware such as Transmission Control Protocol (TCP)/Manufacturing Message Specification (MMS) and Switched Ethernet, to make this standard a future proof standard. The communication mechanism inherited in client-server communication provides the guarantee to the
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delivery of information. However, it makes the transmission too slow to be used for time critical communications. A very high speed peer-to-peer Generic Object Oriented Substation Event (GOOSE) messages and Sampled Analog Values (SAVs) based information exchange from conventional or non-conventional instrument transformers are included in IEC 61850-7-2 that are particularly meant for developing fast and reliable control and protection applications. To increase the dependability, real-time and mission-critical messages such as SAVs from Merging Units (MUs) and GOOSE messages are mapped directly to the link layer of the Ethernet [3], [4]. IEC 61850 GOOSE has an impact on the development and testing of protection applications in modern power system. GOOSE not only provides an opportunity to optimize the system performance at reduced hardware cost but also eliminates the various constraints of traditional protection schemes [5]. Their speed, accuracy and reliability are greatly influenced by the mechanism involved in the GOOSE transmission. Thus GOOSE provides an opportunity to design new condition based enhanced testing and protection schemes. However the overall performance of any communication based protection scheme also depends on the processing capabilities of IEDs, network load conditions and the communication technology. Hence it is crucial to evaluate the performance of these IEDs and their functions to achieve high power system stability and improved power system performance. Thus performance testing for GOOSE based applications must be considered as an important item because this is critical for real-time applications. The performance measurement demands the use of advanced tools that can simulate different power system conditions and status of switchgear equipments (e.g. circuit breaker contacts). Advanced techniques and methodology will help in minimizing the testing procedure; while at the same time will provide better results [6], [7], [8]. The paper presents the requirements of various advanced hardware and software tools, and the methodology for evaluating the performance of IEC 61850 GOOSE protective relays and the associated protection schemes. The rest of the paper is organized as follows: Section II of the paper provides a brief overview of GOOSE message model. Section III discusses communication network aspects in GOOSE message transmission. GOOSE message based timing performance requirements are presented in section IV of the paper. Section
V discusses the configuration process and the strategy for the performance evaluation of IEC 61850 GOOSE based protection schemes. Finally, concluding remarks are provided at the end of the paper. II.
IEC 61850 GOOSE MESSAGE MODEL
Multicasting nature of GOOSE communication enables simultaneous delivery of the same event information to multiple IEDs in its peer group. GOOSE supports the exchange of a wide range of possible common data organized by a DATA-SET. It can be used for the transmission of both binary and analog data such as trip signals and measured values etc. IEC 61850 GOOSE message exchange in the communication network is based on publisher/subscriber mechanism. The publisher writes the value in the local buffer at the sending side; the receiver reads the values from a local buffer at the receiving side as shown in Fig. 1. Specific mapping services of the communication system are responsible to update the local buffers of the subscribers automatically. Values received in the reception buffer at the subscriber side are forwarded to the relevant applications. The standard gives an overview of the classes and services of the GOOSE model. Fig. 1 shows the common components that facilitate the IEC 61850 GOOSE class object [1], different parameters of which are defined as follows: Dataset: The parameter “data set” contains the Object Reference of the DATA-SET (taken from the GOOSE control block, GoCB) whose values of the members shall be transmitted. AppID: This parameter is the identifier of the LOGICALDEVICE (taken from the GoCB) in which the GoCB is located. GoCBRef: This parameter is the reference of the GOOSE control block T (time stamp): This parameter contains the time at which the attribute StNum was incremented. StNum: The parameter “state number” contains the counter that increments each time a GOOSE message has been sent and a value change has been detected within the DATA-SET specified by Dataset. SqNum: The parameter “sequence number” contains t h e counter that increments each time when a GOOSE message has been sent. Test: This parameter shall indicate with the value of TRUE that the values of the message shall not be used for operational purposes.
Fig. 1. GOOSE message service mechanism
ConfRev: The parameter “configuration revision” (taken from the GoCB) contains the count of the number of times that the configuration of the DATA-SET referenced by Data-Set has been changed. NdsCom: The parameter “needs commissioning” contains the attribute NdsCom (taken from the GoCB) of the GoCB and is used to indicate that the GoCB requires further configuration. GOOSEData[1..n]: GOOSE Data contains the user defined information (of the members of DATA-SET) to be included in a GOOSE message. Value: The parameter contains the value of a member of the DATA-SET referenced in the GoCB. To enhance the speed and reliability, a single GOOSE message contains all the required information about the state of an event. To ensure that the GOOSE message is received by the subscribed IEDs in a specified time interval, as demanded by application, GOOSE message has built-in retransmission mechanism that repeatedly broadcasts GOOSE message over the station LAN. To better utilize available network bandwidth, the frequency of re-transmission slows down with each time interval until the hold time expires. To achieve even better level of availability and reliability, GOOSE has a mechanism to ensure that each message reaches to its destination without loss, and any communication failure is reported to substation operator immediately for some necessary corrective actions. Further, a suitable redundant substation communication network architecture is desired to enhance the overall performance of GOOSE based applications [9]. A. IEC 61850 GOOSE Advantages GOOSE replaces a complex network of hardwired connections with an Ethernet network at the station level for inter-IED communication. It brings reduced copper wiring cost along with improved reliability, accuracy and fast signaling response over hardwired schemes for control and protection applications in substations such as interlocking, reclosing, load shedding and Breaker failure protection etc. Thus it can be utilized to improve the performance of control and protection functions of SAS by satisfying the real time performance requirement of these applications for which the transfer time should not exceed 4ms [10]. In the same way, GOOSE service can also be used for testing the performance of protective relays and the associated power system applications. In GOOSE based system, several virtual inputs /outputs are available through software configuration which enables new and improved functionalities to be added in substations in near future, at lower installation, testing and commissioning cost as compared to costly and complicated hardwired schemes. Moreover, monitoring the status of hardwired connections in traditional hardware based schemes is a crucial and difficult task. In communication-based schemes, Ethernet enables supervision of GOOSE messages and virtual connections, for any abnormalities, in the system. If any failure of communication link found in any device or in communication path, it can be rectified automatically or reported to substation operator for necessary action. Thus
GOOSE provides an opportunity to design new and innovative protection applications that can support the self healing capability in substation automation system. III.
COMMUNICATION NETWORK ASPECTS
In SAS, the fast, reliable and precise operation of protection and control schemes depends on the reliable, scalable and deterministic Substation Communication Network (SCN) architecture. Therefore, an effective communication system enables sharing information at various levels of the SAS, which improves the overall reliability, stability and performance of power system and improves management of power flow [11]. Further, to handle bulk substation data from a number of IEDs integrated in substations and to reduce network congestion under severe fault conditions, a suitable substation communication network architecture must be designed to satisfy different levels of redundancy and performance issues [9], [18]. Switched Ethernet technology satisfies the real time performance requirements in substation environments and automation applications by ensuring a full-duplex and collision free environment with deterministic nature [12], [13], [14]. Multicasting with Switched Ethernet allows messages to be sent simultaneously and hence faster. The performance enhancement in GOOSE based applications is achieved by employing a message acknowledgement mechanism and incorporating advanced features in Ethernet frame structure [15]. To reduce the network burden of multicast messages and achieve high network performance, Switched Ethernet possess Quality of Service (QoS) feature that permits time critical messages to be sent on a priority basis thereby minimizes the transmission delay. A 4 byte extension to the standard Ethernet frame header is defined by IEEE 802.1q standard that includes 12 bit field for VLAN identifier and a 3 bit priority tagging field for traffic classification as shown in Fig. 2 [16], [17]. User Priority Field in VLAN tag assigns a priority level to the Ethernet frame. CFI indicates the presence of a Routing Information Field (RIF). Last 12 bits of VLAN tag identifies the VLAN to which the Ethernet frame belongs.
Preamble (7 )
SFD (1)
DA (2or6)
SA (2or6)
TPID (16 bits)
User Priority Field (3 bits)
Tag (4)
Length of Data (2 )
CFI (1bits)
Data (461500 )
FCS (4)
VLAN Identifier (12 bits)
Fig. 2. Extended Ethernet frame [16]
Priority tagging (IEEE 802.1P) feature is used to set the priority for different types of data flow in a network. During network congestion, Ethernet switch identifies the frames with highest priority and then tries to transmit the same frame before the other waiting frames. Time critical protection and control data are set with highest priority whereas measuring and recording event data are set with low priority. Similarly, GOOSE messages can also be prioritized to improve the overall performance of GOOSE based protection functions. It
ensures GOOSE message delivery in a timely and secure manner for real time applications. GOOSE messages may be set with any priority level in between 0 and 7. Virtual LANs (VLANs supported by IEEE 802.1Q standard) permits to form several virtual group of IEDs in the same physically connected network for transmitting data in a secure manner. It prioritizes the transmission of critical information across ports whose are part of the same tagged VLAN thereby minimizes the GOOSE message roaming time on a network. Thus VLAN feature restricts the flow of data to a particular VLAN thereby helps in avoiding network overload condition. Also Switched Ethernet is based on Full Duplex technology thus data throughput is higher with Ethernet switch because it entails no collisions. Rapid Spanning Tree Protocol (RSTP)(IEEE 802.1W) is particularly useful for a larger network where a number of Ethernet switches are utilized for communication and failure of any one component may affect the performance of whole system like in case of GOOSE based substation automation applications. It provides the ability to identify any communication failure in ring network topology and at the same time re-configure the network within a few milli seconds. Thus, it improves the robustness of a star, ring and mesh communication networks against any failed paths. Modern IEDs are therefore designed with two Ethernet ports so that it can automatically switch to back-up port in case the primary port fails. Thus, VLAN, Priority Tagging, RSTP and Full Duplex are some of the key enabling technologies offered by advanced managed Ethernet switches for the realization of high-speed peer-to-peer based real time substation automation applications. These features allow the efficient use of available network bandwidth and minimize the several delays by segregating and prioritizing the Ethernet traffic. The dynamic performance of substation automation architecture in different topologies is analyzed and simulation results demonstrate that the switched Ethernet satisfies the real-time communication needs of SAS [18], [19]. Therefore, utilization of highly robust components and a design of suitable substation communication network architecture increase the availability of GOOSE based applications. IV.
PERFORMANCE EVALUATION PARAMETERS
It is the performance of individual components and the communication mechanism involved in a communication network that decides the quality and correctness of any protection application in power system. Thus, it is imperative to test the performance of IEC 61850 based IEDs to ensure their applicability and the quality of operation under varying system conditions. The timing performance of the GOOSE message transmission is essential to realize their use in real time protection applications. Thus, Protection testing involves the measurement of the overall transfer time as described in IEC 61850-5. The transmission time involved in the transfer of information between two devices is shown Fig. 3 [20].
Fig. 3. Overall Transfer Time [20]
tin, TS
tNET
Network
tNET
tin, DUT
DUT GOOSE Stack tApp DUT Application
tout, DUT
Fig. 4. Times in a round-trip test [21]
Where, ta - Communication processing time within physical device 1 (publisher) to publish GOOSE tb - Transmission time from publisher to the subscriber tc - Communication processing time within physical device 2 (subscriber) to act on published GOOSE Transmission time = t a + t b + t c
tout , TS
Test Application tRT Test Set GOOSE Stack
(1)
IEEE 1588 and Global Positioning System with accuracy of below 1ms are some highly accurate time synchronization techniques for measuring latencies in GOOSE based protection schemes. A time stamped and time synchronized data from IEDs participating in communication network enables measurement of several delays that affects the performance of GOOSE based automation schemes. IEC 61850-7-1 defines several performance classes and messages types for the substation automation functions purposes. The performance criteria of the GOOSE messaging, i.e. transfer time should be less than 3ms for a Trip GOOSE command (class P2/P3) and 20ms for a Block GOOSE command( class P2/P3) as specified in IEC 61850-5 'Communication requirements for functions and device models’. Thus, GOOSE message can be utilized to realize several different substation automation applications that each has different performance requirements. The transmission time of GOOSE message depends not only on communications network parameters but also on network situations and the processing capabilities of the devices used. It involves several latencies that may affect the performance of GOOSE message transfer. Bandwidth, data rate, network load conditions, network configuration and several other factors have to be considered while measuring GOOSE performance as they may affect the speed and performance of GOOSE communication. It is important to design priority tagging and VLAN features based redundant Ethernet network, where message propagation time delay can be minimized to achieve the GOOSE performance of class P1 or P2/P3. Performance testing of GOOSE always presents a great challenge for power system protection engineers and the developments are still going on. In Round Trip Test which is based on the scenario depicted in Fig. 3, GOOSE performance estimation is based on an idea to measure a total round trip time for GOOSE message communication between a test set and a device under test (DUT).
Test set publish GOOSE to a DUT, which is expected to reply via GOOSE as fast as possible. tRT is the round trip time between sending the GOOSE and receiving the response. Fig. 4 shows what times are involved in the mechanism. This method has a conservative approach to measure the GOOSE performance. The statistical estimation of an adequate number of round trip-times gives the average value ( t ) and a standard deviation ( σ ). To calculate the performance of GOOSE, the characteristics of the DUT and the test set are described as in (2) and (3). However the test procedure has various shortcomings and several assumptions have been made to keep the test cases and evaluations simple and easier [21]. t RT − t TS , 2
=
t DUT
σ
DUT
=
σ
2
RT
2
t RT σ RT , σ TS = 4 2 Confidence Interval : [t - k. σ , t + k. σ k ≈ 4 for 99.99% confidence k ≈ 2 . 6 for 99 confidence t TS
−σ
=
Maximum
V.
rating
TS
,
(2) (3 )
]
: t + k. σ
PERFORMANCE EVALUATION METHODOLOGY OF IEC 61850 GOOSE
GOOSE based protection schemes offer significant advantages over conventional hardwired schemes but also present big challenges for a protection engineer while configuring IEC 61850 based devices. For this it is important to understand the functionality of advance tools and the techniques for their successful implementation in the protection applications. Hence protection engineer must be acquainted with proper test documents, tools and troubleshoot schemes not only for reducing testing and troubleshooting time but also to improve overall system reliability and availability. Fig. 5 shows the laboratory test setup for performance measurement of GOOSE based protection scheme. Where protective relay(s), Test set, and a PC are connected to an Ethernet Switch to form a communication network. An implementation scheme for the performance measurement of IEC 61850 based protection relays and the associated protection schemes involve the following steps.
Fig. 6 shows the snapshot of the GOOSE message configuration where the Relay IED_0001 is made a member of IEC 61850 station, which is then configured to publish GOOSE message data item IED_0001/PROT/PTRC1/Tr/General for the test set. In the network area of this module, the Siemens relay provides the ability to set the priority levels for the GOOSE service as low, medium and high priority. Fig. 5. Laboratory Test Setup
A. IEC 61850 Substation Configuration Process In IEC 61850-6, the functional and communication capabilities of devices and the system configuration are described in a standardized way using XML (eXtensible Markup Language) based SCL file. Various bay level IEDs, their interconnection and the SA functions in SAS are represented using SCL files to achieve communication interoperability and reduction of design efforts. This feature in IEC 61850 enables automatic configuration of devices to share device information among the users [3]. A configuration tool plays an important role to set various parameters of individual IEDs as per the designed protection scheme, and at the same time in establishing communication link between them. Any wrong parameter setting may lead to a false operation when correct operation would be crucial. The configuration tool generates various SCL files for facilitating substation engineering process in the project. The primary task in the GOOSE configuration process is the configuration of individual IEDs which are being communicating in the substation project. Initially, using the Siemens configuration tool - DIGSI 4.80, a Distance relay (7SA610) named here as IED_0001 is configured to generate ICD (IED Capability Description) file as per the designed protection scheme [22], [23]. ICD file, which contains all information about the IED, is downloaded in an IED to enable its configured functions. These files are further required for the configuration of the system. For this, these files get imported into the DIGSI system configurator for the configuration of GOOSE messages in substation by specifying the publishers and the subscribers of these messages. The system configurator tool creates the SCD (Substation Configuration Description) file that describes the relationship among the IEDs in the substation automation project and the description of the GOOSE.
B. GOOSE Configuration Module Using GOOSE Configuration Module under Omicron’s Test Universe Software, Omicron CMC 256 + test set is configured to publish and subscribe GOOSE messages [24]. The test set is able to simulate and subscribe to GOOSE messages. The subscription of the test set to GOOSE messages, published from the relay, is based on importing SCD file in Omicron’s GOOSE configuration module. The status information contained in the published GOOSE message from the relay is mapped to its binary inputs as shown in Fig. 7. It needs to ensure that published GOOSE messages must map to correct binary inputs of test set. The information from an SCD file is the GOOSE messages that a particular IED will subscribe and publish.
Fig. 7. GOOSE Message Configuration View of Test Set
Both the DIGSI 4.8 software and Omicron’s Test Universe software are housed in a separate computer, which is also connected to the Ethernet switch. A network protocol analyzer can monitor the network traffic and time synchronized data from IEDs under test to evaluate the protection scheme performance. Thus the GOOSE messages that were on the network during the test and their timings are continuously monitored by network protocol analyzer. C. Test Configuration
Fig. 8. Test Configuration Module View
Fig. 6. GOOSE Message Configuration View of Distance IED via DIGSI 4.80
After the relay and the test set are suitably configured to publish and subscribed GOOSE messages, the test set is simulated to generate fault signals using the ‘State Sequencer
Module’ under Omicron’s proprietary software ‘TEST Universe’ as shown in Fig. 8. It can simulate different fault conditions on a power network to generate fault waveforms of voltage and current signals [25]. The signals so generated under abnormal system conditions are injected to the relay for performance evaluation of the designed protection scheme. Based on the fault currents and voltages signals injected, relay calculates the location, duration and other parameters of the fault. The user is able to configure the type and the location of the fault. It can configure different types of faults such as single line to ground fault, phase-to-phase fault or three phase fault along with type of testing method. Upon completion of the distance relay’s operating characteristics performance testing. The next step is to design a suitable protection scheme and implements the similar testing procedure to evaluate its performance. Thus the robustness of the protective relay and the protection scheme can be tested for different fault types and various fault zones.
[2]
[3]
[4]
[5]
[6]
[7]
[8]
D. Test Report [9]
[10]
[11]
[12] Fig. 9. Time Signal View
[13]
It is possible to view, measure, and record the test object responses as functions of time and analyzed either automatically or manually after the test. Fig. 9 shows the snapshot of ‘Test Signal View’, under state sequencer module, where voltage, current, binary states and state transitions are shown as a function of time. Interactive time measurement is possible within time signal view. It is also possible to generate test reports based on user defined format and assesses test as either “passed” or “failed”. CONCLUSION A GOOSE message service model and the communication network features are explored in depth to study its impact on the performance of GOOSE based power system protection applications. Advanced hardware and software tools which are used for simulating power system conditions and the other binary status or trip signals have been used for demonstration. The paper presented the laboratory setup and the methodology for the performance evaluation of GOOSE based protection schemes. Communication based protection schemes offer significant advantages over conventional hardwired schemes but the major challenges encountered is the successful configuration of IEC 61850 based devices and the system . REFERENCES [1]
IEC 61850: “Communication Networks and Systems in Substations”, 2002–2005 (www.iec.ch).
[14]
[15] [16]
[17] [18]
[19]
[20] [21]
[22] [23] [24] [25]
R.E. Mackiewicz, “Overview of IEC 61850 and Benefits”, IEEE PowerSystems Conference and Exposition, PSCE’06, Atlanta, Oct.29Nov.1 2006, pp .623–630. K.P. Brand, “The Standard IEC 61850 as Prerequisite for IntelligentApplications in Substations”, IEEE Power Engineering Society General Meeting, 6-10 June 2004, pp. 714–718. T.S. Sidhu and P.K. Gangadharan, “Control and Automation of Power System Substation using IEC61850 Communication”, Proceedings IEEE Conference on Control Applications , Toronto, Canada, 28-31 August 2005, pp. 1331–1336. M.C. Janssen and A. Apostolov, “IEC 61850 Impact on Substaion Design”, IEEE/PES Transmisssion and Distribution Conference and Exposition, Chicago, 2008, pp. 1-7. B. Vandiver, “Testing of UCA Based Microprocessor Based Protective Relays”, IEEE Power Engineering Society Summer Meeting, vol. 1, July 2002, pp. 294–296. N.N.-Dinh, G.-S. Kim, and H.-H. Lee, “A study on GOOSE communication based on IEC 61850 using MMS ease lite”, in Proc. 2007 International Conference on Control, Automation and S ys t e ms , 17-20 Oct. 2007, pp. 1873 –1877. A. P. Apostolov., “Implementation of accelerated transmission line protection schemes in substations with IEC 61850”, IEEE/PES Transmission and Distribution Conference and Exposition, 21-24 April 2008, pp. 1 – 6. I. Ali and M. S. Thomas, “Substation Communication Networks Architecture”, POWERCON & IEEE Power India Conference, New Delhi, India, October 2008, pp. 12–15. A. G. Phadke and J. S. Thorp, “Computer Relaying for Power System”, Taunton, Somerset, England, Research Studies Press, and Wiley, New York, 1988. V.C. Gungor and F.C. Lambert, “ A Survey on Communication Networks for Electric System Automation”, Computer Networks, vol. 50, no.7, pp. 877-897, May 2006. K. C. Lee and S. Lee, “Performance evaluation of switched Ethernet for real-time industrial communications”, Elsevier Computer Standards & Interfaces, vol. 24, no. 5, pp. 411–423, Nov. 2002. T. Skeie, S. Johannessen, and C. Brunner, “ETHERNET in substation automation”, IEEE Control Systems Magazine, vol. 22, no. 3, June 2002, pp. 43–51. J.D.Decotignie,“Ethernet-Based Real-Time and Industrial Communications” , Proceedings of the IEEE, vol. 93, no. 6, pp. 1102– 1117, June 2005. C. Hoga, “New Ethernet Technologies for Substation Automation”, IEEE Power Tech, Lausanne, 1-5 July 2007, pp. 707–712. Z. Wang, Y. Q. Song, J. Chen, and Y. Sun, “Real time characteristics of Ethernet and its improvement”, Proceedings of the 4th World Congress on Intelligent Control and Application, June 2002, pp. 1311–1318. M.P. Puzzuoli and R. Moore, “Ethernet in the Substation”, IEEE Power Engineering General Society Meeting, 2006, pp. 1–7. M.S. Thomas and I. Ali, “Reliable, Fast, and Deterministic Substation Communication Network Architecture and its Performance Simulation”, IEEE Transactions on Power Delivery, vol.25, pp. 2364–2370, Oct. 2010. T.S. Sidhu and Yujie Yin, “Modelling and Simulation for Performance Evaluation of IEC61850-Based Subsation Communication Systems”, IEEE Transactions on Power Delivery, vol.22, no. 3, pp. 1482–1489, July 2007. IEC 61850-5: Communication Requirements for Functions and Device Models, IEC INTERNATIONAL STANDARD, July 2003. B. Bastigkeit, T. Schossig, and F. Steinhauser, “Efficient Testing of Modern Protection IEDs”, In: PAC World, vol. 3, 2009 Winter, pp. 54– 59. Reference Manual, “SIPROTECH 4”, SIEMENS Ltd. Reference Manual, “DIGSI 4”, SIEMENS Ltd. Reference Manual, “GOOSE Configuration”, OMICRON Electronics. Reference Manual, “STATE SEQUENCER”, OMICRON Electronics.
