B INTERUCA Project: UCA interoperability for distributed control within electrical substations

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1 21, rue d'artois, F Paris B5-204 Session 2004 CIGRÉ INTERUCA Project: UCA interoperability for distributed control within electrical substations IKER CANALES * PEDRO IBAÑEZ JUAN TORRES ENRIQUE GARCIA ROBOTIKER ROBOTIKER IBERINCO IBERDROLA (Spain) (Spain) (Spain) (Spain) FERNANDO COBELO JUAN A. URQUIZA JOKIN GALLETERO ZIVP+C TEAM-Arteche GE Power Management (Spain) (Spain) (Spain) The most recent proposals to adopt a standard for substation control and protection systems (UCA and IEC 61850) involve enormous implications for manufacturers and users, both developing the new Intelligent Electronic Devices (IEDs) and in the way of how to specify new integrated systems and related applications. The objective of INTERUCA Project is development and implementation of a pilot installation based on recent standard IEC 61850, Communications networks and systems in substations, within a real electrical substation, in order to verify and demonstrate interoperability among IEDs from different suppliers and, at the same time, to analyze advantages and disadvantages given by this new architecture regarding current state of technology, as well as to obtain experience about implications derived from adopting the new standard, thus making a significant contribution to its deployment and consolidation (unified interpretation) and going forward on the way of developing products compatible with it. Keywords: Communication - Protocol - Protection Control IEC INTRODUCTION Since digital technology appeared and incorporated into control and protection systems, it is becoming an imperative need to be provided with an open communications standard which allows users to achieve interoperability among IEDs from different manufacturers [1]. Cost reduction pursued by means of control and protection systems integration using communications networks will not be a true advantage until a real open solution is available, which makes forget typical problems related to proprietary protocols and networks, future system maintenance, intermediary protocol converters, etc. In the middle 90s, two standardization activities were initiated in this respect: Utility Communication Architecture (UCA) project within EPRI world, and Working Groups 10, 11 and 12 from TC 57 within IEC world. * ROBOTIKER, Tecnalia Technology Corporation, E Zamudio - Bizkaia (Spain). iker@robotiker.es

2 In this sense, and taking UCA 2.0 as starting point, IEC has recently finished the definition of standard distributed object-based communications architecture IEC 61850, which not only keeps UCA 2.0 compatibility, but also increases its functionalities, offering interoperability among devices supplied by different manufacturers over the same data network, besides high-speed real-time data exchange and peer-to-peer communications [2]. 2. INTERUCA PROJECT In view of all this interest generated by recent standard IEC 61850, and as a result of the initiative of enterprises involved into substation control and protection equipments installation process (manufacturers, engineering and utility), along with the participation of a technological center, in early 2001 the INTERUCA Project is proposed in order to test within a real pilot substation the kindness of new IEC standard, previously adapting to it devices utilized for substation management, control and protection. The range of INTERUCA Project s participants comprises: manufacturers and suppliers of control and protection equipments, who have to make HW and SW modifications for adapting them to new communications architecture; final users (electric energy distribution companies) and system integrators (engineering companies) of those IEDs within an electrical substation, who have not only been taking part while specifying requirements, but also supervising integration tests, validating system architecture and assessing all developed products before their later utilization; and a technological transference center, that developed a HW/SW platform independent IED middleware and helped manufacturers with everything related to the rest of communications architecture layers Objectives The objectives of INTERUCA Project are the following: To obtain experience at interpretation of new standard IEC 61850, checking out the feasibility of its adaptation and finding out their advantages and disadvantages given by its implementation. To verify in an efficient way interoperability among devices supplied by different manufacturers: message exchange through peer-to-peer communication schemes, real-time data transmission, time synchronization, Validation of transmission time requirements, mainly in the peer-to-peer level, through this new communications architecture. Checking out communications system robustness in a noisy environment with particular electromagnetic compatibility problems, as well as simulation of excessive network traffic and verification of system response in such a case. To cover all these goals, IEDs provided by three different manufacturers were adapted according to standard IEC and, with help of an engineering company, tested in a real pilot installation conveniently suited by an electric energy distribution company [3][4] Description of the technical solution IEC as standard data communications architecture... Despite the lack of maturity of standard IEC compared to UCA 2.0 at the beginning of this project, both manufacturers experience and active participation of all Consortium members in Working Groups of Spanish Committee of TC 57 supported the idea that final UCA convergence is its compatibility with IEC 61850, as well as once edited, all IEC standard documents will be the worldwide reference for developing new control and protection systems. Ethernet TCP/IP as physical layer... 2

3 Taking advantage of the new communications architecture, which employs MMS and TCP/IP over Ethernet, an assessment on state-of-the-art industrial Ethernet related technologies and commercial products was made in order to test operation of these systems under the particular noisy environment of substations. Technical solution proposed by IEC standard permits to benefit from other innovative aspects when using LAN network technologies (Ethernet and TCP/IP) for substation communication bus, being able of accessing data through typical Internet tools, like web-browsers, and making possible not only its integration with another enterprise networks, but also an easy migration to another IP networks. Wiring was made by means of a configurable multiport Ethernet switch, with devices connected at 10 Mbps fiber optic and devices connected via Fast Ethernet at 100 Mbps twisted pair in CAT5 10/100 Mbps. Although nowadays it seems that unique viable solution is fiber optic so as to support time requirements with regard to quickly transients, it was decided to test system operation using twisted pair as well. An MMS API from third party developer... As help with Consortium suppliers product adaptation tasks, the technological center developed a common part for all of them: the application levels of IEC architecture (layers 5, 6 and 7 of OSI reference model), based on MMS protocol, which comes from industrial automation world and is highly complex. However only a reduced set of all the possible MMS services has to be implemented for meeting new communications architecture requirements, so in certain way, development of that common part is a little simplified. Development of this MMS services library, compared to the possible utilization of a commercial library, has implied advantages, but also disadvantages [5][6][7]. An important effort has been required both by the technological center while developing it and by every manufacturer while integrating it on every particular platform which, by the way, is different to that used during the MMS library development. Integration of this own MMS library has involved making a lot of tests, but it has also allowed detection and correction of some problems during this integration phase itself, not later. Another advantage from selecting this alternative is availability of MMS library source code and active participation of its developer, the technological center, when debugging and testing, which allows manufacturers to be ready to make any modification or future extension. Following with the above mentioned adaptation of their current IEDs, every manufacturer of the Consortium first takes charge of design and development of a new HW platform, and then implements the remaining levels of communications architecture, which are both transport levels (layers 4 to 1 of OSI reference model) and user level (the user application itself). Main repercussion of HW adaptation is a directly increasing of new devices cost, whereas SW adaptation implies a considerable processing load on IEDs compared to existing serial communications solutions, which causes new communications modules to consume a lot of device resources regarding memory and processing capacity. HV/MV substation as the pilot installation... Guernica 30/13 kv substation was chosen as the pilot installation, comprising two 30 kv line positions, two transformers and eight distribution lines connected to two MV bars. In this pilot substation all of the new control and protection devices, once adapted and validated according to IEC standard, were connected in a parallel way to IEDs already installed on it. For achieving this compatibility with IEC 61850, HW/SW modifications were needed: adaptation to new data model and associated communications services (both adaptations are specified as result of stating exactly functions and data that must be included into devices); incorporation of a TCP/IP communications 3

4 stack over Ethernet; integration of the referred MMS services library; implementation of peer-to-peer communications schemes; etc. Likewise, this pilot installation is monitored through a telecontrol connection under IEC standard. The Substation Central Unit (SCU) is responsible for both collecting all information from the rest of IEDs through substation bus and then converting those data to IEC protocol in order to transmit them from substation to dispatch center (see figure 1). Fig. 1. MV substation architecture for INTERUCA Project. From a user s point of view, substation system must meet these requirements: Interoperability among IEC devices from different suppliers, and compatibility at message exchanging and peer-to-peer communication schemes with IEDs from INTERUCA Project. Peer-to-peer communications among any substation devices with a maximum delay of 10 ms. Improvement of IED time synchronization precision within electrical substation with regard to SCU, admitting a maximum error of 1 ms. Remote access to all protection related data (oscillography, events, settings, status, ), as well as possibility to remotely adjust protection settings. With that purpose SCU is connected to information systems of the utility, thus those data will be available via its intranet. Also substation IEDs must allow local access to all protection related data, besides visualization and adjustment settings using the central HMI and at least utilizing tools in the style of browsers. Directional overcurrent as the protection functions... In order to make a real implementation of data models, and taking into account features of the selected substation, all Consortium members decided to include the logical nodes related to phase and ground directional overcurrent protection functions. Moreover this simple election permitted Consortium members to inspect interpretation of logical nodes for measurement and metering, logical nodes for generic references, etc., according to their definitions in IEC standard. However, it also was useful to confirm that the number of standard data and attributes defined in some logical nodes of IEC x is small compared to values and settings usually employed for commercial IEDs, and in some others is large. This implies that, and despite the common rules given by IEC standard for incorporating new data and attributes, every manufacturer can and must do his own interpretation and implementation. Within INTERUCA Project an important work has been made so as to reach a consensus on a common IEC profile to be used by all Consortium members. As a result of this, a specification about a line protection relay IEC profile has been obtained, for which it were utilized both standard logical nodes defined in IEC x and, because of an extension of IED capabilities, new data and attributes defined according to rules provided by IEC standard itself. 4

5 2.3. Project planning INTERUCA Project has been developed over the last 3 years ( ) in three different phases: Stage 1: Technical specifications and requirements (2002). Stage 2: System architecture design and development (2003). Stage 3: Installation and functional tests (2004). 3. THE MMS LIBRARY IEC standard keeps user applications separate from the communication stack. This goal is achieved by defining an independent interface composed of abstract application objects and services and called Abstract Communication Service Interface (ACSI). What makes real the local ACSI implementation is its mapping to all available services of the concrete application layer and communications profile by means of the Specific Communication Service Mapping" (SCSM). That is, services which are truly sent through the network are the specific ones defined in SCSM, not the ACSI ones. Therefore it is necessary to use an abstract data model in order to make IEC standard independent of specific technologies and to give it validity along time. This is the reason why the MMS library has these technical specifications: Mapping of all ACSI services (abstract), which are required by data models defined in IEC x, to MMS services (real). As mentioned above, with this mapping the user application does not depend on communication stack implemented. It means that the user application will keep being valid in spite of changing the current SCSM defined in IEC Finally, it is convenient to explain that not all the communication profiles supported by this part 8-1 need for a MMS mapping, but this mapping is required in the most of communication functions. Well-documented MMS library interfaces with the rest of SW modules that make up every of the devices (see figure 2): o Interface with lower layers (transport levels) o Interface with the upper layers (user level). ANSI C programming following a modular design, so as to be able to create distinct MMS library versions (adding or removing services) during the design and development stage of INTERUCA Project (stage 2), both for checking out the correct operation of MMS library and for making easy devices SW integration tests. Fig. 2. Logical location of the MMS library. As for the MMS library operation (see figure 3), user applications request abstract services defined IEC x (ACSI services). Then MMS library processes and maps them to MMS according to IEC (so MMS services and their parameters generate the appropriate PDU defined by ISO- 9506), sending them through substation network using services provided by the transport layers of IEDs. Remote user applications receive indications of the requested abstract services and process them, using their local data models if necessary and sending the response by means of the MMS library again. 5

6 Fig. 3. General diagram of the MMS library operation. The ACSI interface proposed by IEC standard consider 14 different models (server, logical device, logical node, ), and every of these models comprises a specific set of services. These ACSI services, with independence from the model,are mapped to MMS utilizing five distinct combinations of the so-called T-Profiles and A-Profiles (the former profiles cover specifications and interrelations of the four lower layers of the OSI reference model, and the latter profiles cover the three upper layers). Thus the MMS library implements the following set of ACSI services to perform information exchanging among IEDs: Client-Server services and communication profiles. Generic Substation Event (GSE) management services and communication profiles. Generic Object Oriented Substation Event (GOOSE) management services and communication profiles. Generic Substation State Event (GSSE) management services and communication profiles. Time synchronization. Mapping to MMS of these five groups of ACSI services is specified in IEC , as well as both services and protocols which must be used in every layer of OSI reference model that composes the T- Profile and the A-Profile of those groups. Services and protocols specifications of the MMS library is shown in next Figure 4, and it takes into account that TCP/IP over Ethernet solution is the alternative chosen within INTERUCA Project. Fig. 4. Services and protocol specifications for all ACSI services groups. 6

7 The MMS library thoroughly provides a definition of all its interfaces and a specification of its service primitives (that is, name of functions and parameters needed), both for ACSI services which must be supplied to the upper layer (user application) and for services which are requested to the lower layers (T-Profiles): Interface that provides connection-oriented transport services based on TCP/IP for the Client- Server services and communication profiles. Interface that provides direct access to data-link layer (Ethernet) for the GOOSE and GSE management services and communication profiles. Interface that provides connection-less transport services based on OSI for the GSSE services and communication profiles. Interface that provides connection-less transport services based on UDP and ICMP for the time synchronization. 4. PEER-TO-PEER COMMUNICATION: A PROTECTION COORDINATION EXAMPLE To test the real possibilities of peer-to-peer communications, a protection coordination of instantaneous overcurrent units was issued. This function is a new solution to improve operating time under bus faults where busbar differential protection does not exist. This is an example of a scheme requiring the transference of protection related data among different devices. This scheme allows for the use of the instantaneous overcurrent unit at the low side of the transformer feeding the busbar, in order to provide a fast trip in case of a fault in the busbar. So as to coordinate with instantaneous units at the feeders, any pick-up signal from the feeder relays must be sent to the transformer relay to block its instantaneous unit (see figure 5). GOOSE messages are then sent from line units to transformer units. Fig. 5. Representation of a fault in a feeder. To have a complete test of compatibility between IEC and UCA 2.0, it has been arranged that the transformer unit is a UCA 2.0 protection device whereas line units are protected by IEC devices. An offset coordination time at the transformer unit must be set to a minimum of 50 ms. 5. CONCLUSIONS Some relevant conclusions to be presented as a consequence of INTERUCA Project development are the following: In opinion shared by all of the three manufacturers who have participated, adoption of new IEC standard involves developing a new product line for control and protection equipments. Adaptation to new IEC data models implies such a modifications on IEDs that it is not only a new protocol implementation, but the development of completely new devices. Apart of enormous effort made by the standardization group, and despite the voluminous documents which comprise IEC standard, there are still some points that need for a harmonization of interpretation. Therefore it is understood that spending time on achieving this 7

8 harmonization among the different manufacturers is still necessary in order to truly develop 100% IEC standard compatible devices. Because of the great amount of processing resources required by prototypes, some difficulties have been detected both during development process and when trying to get a peer-to-peer communication response time of 5ms. For system specifications, a special training and a deep knowledge will be needed for users. Likewise, it is indispensable that certification organizations go forward on defining degrees of compatibility with IEC standard due to the wide range of compatibility that can be given. From a functional point of view, the new standard opens the possibility of developing a great number of applications via communications, with an increasingly reduction of traditional wiring. Reliability and performance of the system will highly depend on design of the communications network that support it. 6. ACKNOWLEDGEMENTS We acknowledge Basque Country Government for its economical contribution, through INTEK Programme, to INTERUCA Project over its three-year duration. 7. REFERENCES [1] C.R.Ozansoy, A.Zayegh, A.Kalam, Communications for substation automation and integration (Australasian Universities Power Engineering Conference AUPEC2002, Melbourne, September 2002). [2] Karlheinz Schwarz, Standard IEC for substation automation and other power system applications (International Conference Power Systems and Communications Infrastructures for the Future, Beijing, September 2002). [3] Mark Adamiak, Drew Baigent, Design and Interoperability Testing of a Network IED: A Manufacturer s Perspective ( pm/notes/netwkied.pdf). [4] Mark Adamiak, Ashish Kulshrestha, Design and Implementation of a UCA based Substation Control System (Protective Relaying Conference, Atlanta Georgia, May 2001, [5] Herbert Falk, Jeffrey Robbins, An Explanation of the Architecture of the MMS Standard (Rev /02/95, [6] Industrial automation systems Manufacturing Message Specification Part 1: Service definition (ISO/FDIS :2002(E)). [7] Industrial automation systems Manufacturing Message Specification Part 2: Protocol specification (ISO/FDIS :2002(E)). 8