Integration of Control, Protection and Supervisory ...

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Integration of Control, Protection and Supervisory Systems in Hydro Power Plants - State of Art and Trends Erick Fernando Alves, Member, IEEE, Masato Lúcio Yano, and Marcus Hofmann

Abstract—This paper seeks to present and analyze: the new distributed control, protection and supervisory systems that are starting to be applied on hydro power plants; to point out the main differences over centralized systems; and to comment trends in their development.

systems in hydro power plants and section V describes the actual state of art on the subject. Finally, section VI presents the actual trends and new challenges.

Index Terms—Hydroelectric power generation, automation, distributed control, communication standards.

II. FACTS AND F IGURES

I. I NTRODUCTION HE control, protection and supervisory systems of hydro power plants faced significant changes in recent years. With the evolution of digital processors and high capacity communication systems, the cluster of panels containing electromechanical and static devices were substituted by IEDs (Intelligent Electronic Devices). However, most part of digital systems currently in operation is composed by independent subsystems, with a limited level of communication between them. As result, each subsystem in a hydro power plant (SCADA, protection, voltage regulators, speed governors, among others) interacts with the process entirely independently from the others. This situation leads to a multiplication of wired signals (currents, voltages, temperatures, equipment status and alarms, commands etc.) that are brought from the process up to the IED location, entailing considerably the installation complexity (amount of cables and panels, conduits, ducts, passing boxes) and the interface hardware needed. The final result is a increased overall cost of the project. To avoid this situation, the integration of IEDs using distributed systems philosophy and reliable local area networks (LANs) with open protocols like IEC 60870-5-101/-103/-104 and IEC 61850 is proposed. The directs consequences are the reduction of interface points, the cost of equipments and installation services while offering the operation and maintenance teams a wider range of information. This solution corresponds to the state of art in the automation of power plants [1] [2] [3]. Section II presents facts and figures from the power sector and the political and technological vectors that are leveraging changes in systems integration. Section III briefly describes the concepts of hydro power plants automation and the basic differences between distributed and centralized systems. Section IV lists the actual limitations to the application of distributed

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E. F. Alves, M. L. Yano and M. Hofmann are with Systems Engineering Department of Voith Hydro, São Paulo, Brazil (e-mail: [email protected], [email protected], [email protected])

According to Macmillan Dictionary [4], integration is ”the process of combining with other things in a single larger unit or system”. In automation engineering is usual to define it as the expertise of doing several independent subsystem work together and to assure that they present to the end user as a single and consistent system. The integration of systems in the power generation sector is a controversial issue. Since it is a basic service to the modern society, both fail as improper operation in a power plant can result in large losses: damage to equipment, life-threatening, wide out of service period, huge loss of revenue, and other economic and social damages, often higher than the previous ones [5]. The demanding requirements of the power sector in conjunction with such serious potential consequences tend to make the engineers of this area quite conservative and wary of accepting new technologies. The main reason not being actual technology limits, but the users resistance to new applications which they do not dominate completely [3]. On the other hand, the worldwide electric power sector changes in the last decades, mainly the open market philosophy and the regulatory agencies start off, brought pressure for broad operational and economic efficiency. Minimum technical standards were required as well as the availability of a huge amount of data, bringing about the modernization and digitalization of power plants. In parallel to the political changes, many technological advances were also happening: • The evolution of high-end digital processors made possible to adopt programmable logic controllers (PLCs) as data acquisition and control units (DACUs) and, in the last years, also as digital speed governors (DSGs) and automatic voltage regulators (AVRs); • The progress on the digitalization of protection relays also bring new possibilities to them, like: use of complex logic decisions, programmable I/Os, advanced electrical measurements, communication ports etc. Consequently, these equipments expanded their functions and now are performing control and measurement functions, previously exclusive to DACUs and bay controllers.

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Fig. 1.

Typical structure of a hydro power plant automation system

As result, the early specific and dedicated equipments for control, protection and supervision of hydro power plants are more and more giving way to others extremely flexible: the Intelligent Electronic Devices (IEDs). The application and integration of IEDs in the design of hydro power plants are allowing a higher level of systems decentralization, bringing intelligence and communication capacity to the lower levels of the process. This implies in: drastic reduction of interfaces, simplified design, flexibility in operation and maintenance, possibility of future expansions [1] [3]. As consequence, technological advances are converging to the political changes: robust communication channels, IEDs and interconnected computer networks allow the build up of quality, information and efficiency in the services of generation, transmission and distribution of electric power [6] [7]. III. C ONCEPTS In automation systems of hydro power plants there are two hierarchical levels: the process interface and data acquisition level; and the command and supervision level, also called central system [8]. This hierarchy is presented in Fig. 1. The DACUs are present in the process interface and acquisition level, being responsible by the intelligence of the commands and all the data transfer from the process to the command and supervision level. Usually they are connected to the central system by a local area network (LAN) based on Ethernet or by communication processors (gateways). The last ones have the task of converting the information from DACUs to a standard acceptable by the central system and to transfer it to the Ethernet LAN. In the process level some specific IEDs for hydro power plants automation are present. An IED is a device that has one or more microprocessors and the ability to receive and to send data and control signals to an external equipment [9] [12].

With its incorporated microprocessing and communication power, this device provides: • Self and external circuitry monitoring; • Real time synchronization for events sequencing; • Diversification of the control possibilities; • Data acquisition for system analysis. Examples of IEDs in hydro power plants are: PLCs, digital protection relays, intelligent remote units, speed governors and voltage regulators. The processing and communication capacity of these equipments open up new concepts for system integration, like the use of distributed systems. A distributed system is a collection of autonomous devices interconnected by a communication network and equipped with software that allows system resources sharing: hardware, software and data [10]. The most important difference between distributed and centralized automation systems is the way the communication is done between the subsystems. In a centralized system, it is done by mean of variables in a shared memory area, using a master-slave model. However, in a distributed system such shared memory area does not exists, so all the communication concept should be reworked to make use of messages, usually adopting a client-server model. Distributed systems are widely used on the command and supervision level of hydro power plants, an example shown in Fig. 2. IV. ACTUAL L IMITATIONS As the determinism is crucial for the process level, the connection between the IEDs in this level and the DACUs are done by field buses based on IEC 61558 standard (e.g. Profibus DP) or hardwired. Meanwhile field buses based on IEC 61158 have some characteristics that limit the application of distributed systems on the process interface and data acquisition level, preventing the use of full capacity from IEDs processing and

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Fig. 2. Typical distributed architecture on the command and supervision level of a hydro power plant automation system

communication. One of the main are the use of RS-485 and the master-slave architecture. Another is the unavailability of time stamps in most part of the available protocols, rendering impossible the sequencing of events. Finally, equipments with serial communication from a wide range of suppliers are real barriers in the integration engineering due to the lack of standardization. As result, each subsystem in a hydro power plant (SCADA, protection, voltage regulators, speed governors, among others) interacts with the process entirely independently from the others. This situation leads to a multiplication of wired signals (currents, voltages, temperatures, equipment status and alarms, commands etc.) that are brought from the process up to the IED location, entailing considerably the installation complexity (amount of cables and panels, conduits, ducts, passing boxes) and the interface hardware needed. The final result is a increased overall cost of the project. Taking into account these limitations, specific protocols for the automation of power systems were developed. Since the end of 1980’s, the need for a standardized communication between digital equipments of different manufacturers had been identified. The integration of digital protection relays were essential to advanced schemes of operation and protection of the power system. With this purpose, IEC 60870-5 standards were created, which applies to telecontrol equipment and systems with coded bit serial data transmission for monitoring and controlling geographically widespread processes [11]. The protocols IEC 60870-5-101/-103/-104 were successful attempts to implement the firsts distributed systems and to integrate intelligent devices in the electric power system, especially in substations. Today they are unquestionable standards of open communication protocols in the electric power sector. However, due to technological limitations of the time they were designed, the models are simple and prevent the use of client-server architecture to its fullest. With IEC 608705 protocols, the absence of modeling and intuitive naming of data and devices in a hierarchical and structured way hampers interoperability. Thus, each project has its special characteristics, what makes seamless integration not possible

Fig. 3.

Hierarchy of the IEC 61850 data model [12].

and increases costs of engineering, testing, commissioning and maintenance of the legacy hardware and software. V. S TATE OF A RT Having in mind these challenges, since 1995 the IEC has formed a group to set a new standard that would meet the needs of substation automation. This group responded to the concern up to that time and created the IEC 61850. The main objectives were: • Develop a single protocol for complete automation of electrical substations considering the modeling of the different data required; • Define the basic services for data transfer, so that the complete mapping of the communication protocol could be done ”future-proof”; • Promote interoperability between systems from different manufacturers; • Provide a common format for data storage; • Define a complete list of tests required for equipment that meet the standard. Recently, the standard is being updated to be applicable to the entire chain of the electric power sector: generation, transmission and distribution [14]. To achieve the objectives described, IEC 61850 provides a complete client-server architecture and uses the object oriented approach. For this, divides the functions in objects called logical nodes that communicate with each other. Each node has its own logical data set and they are shared with other logical nodes according to rules called services. The logical nodes are grouped into logical devices, which are contained in servers, the actual IEDs. This architecture is shown in Fig. 3 and allows the sharing of hardware, software and data between IEDs and eliminates all limitations of field buses. Additionally, the protocol proposed by IEC 61850 provides mechanisms to meet the critical time to exchange information

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at the process level, ensuring the safety of the hydroelectric power plant protection and control functions. For this, its communication interface uses the concept Publisher Subscriber, that through multicasting and use of intelligent switches restricts the data flow to only the devices interested in the information. The block diagram of this concept is presented in Fig. 4.

Fig. 5. Fig. 4.

Integration of PLCs in a IEC 61850 network using gateways.

IEC 61850 communication interface [12].

VI. T RENDS The use of distributed systems at hydro power plants in command and supervision level is a reality for many years. And with the evolution of networks and communication protocols, applications in the interface and data acquisition level as well as in the process level begin to take its first steps. The distribution of control and protection functions through the use of the protocol defined by IEC 61850 in substations associated with hydro power plants is already quite common, following the trend of the transmission and distribution markets described in [1], [6], [2], [7], [9]. However, the integration of these products to DACUs and other systems of the hydroelectric plant is still a challenge that has not been fully addressed [14]. The current solution in hydro power plants is to use gateways to convert data into a protocol that could be processed by the PLCs, as shown in Fig. 5. On the other hand, gateways limit the full implementation of all the advantages of IEC 61850, as they convert data to protocols that use polling. Thus, the data speed exchange between the IEC 61850 compliant IEDs and PLCs will be limited by the cycle time of the field bus or the gateway, as presented in Fig. 6. In an application recently developed by Voith Hydro in Germany, an update time of 50 ms was achieved using MMS, GSSE and GOOSE messages. This represents a significant evolution, allowing the decentralization of mechanical subsystems functions, where this update rate is enough. The distributed philosophy turns the automation system of hydroelectric power plants more robust and reliable. As horizontal communication is available in the process and in the interface and acquisition levels, in a failure of a DACU, the subsystems may decide to continue operating normally, starting a restricted mode of operation or an emergency stop. Nevertheless, the use of gateways still prevents the sharing of data for time-critical electrical subsystems using GOOSE and SMV, like trip signals, interlocking, measurements of generator electrical quantities for regulation purposes and events for sequencing of events. To overcome these limitations, it is essential that in the coming years the manufacturers

of PLCs present solutions for native communication in IEC 61850 networks. With this technological barrier overcome, the tendency to use distributed architecture automation systems in power plants could be strengthened. VII. C ONCLUSION With the advancement of digital processors and communications systems, information technology, distributed computing and telecommunications have converged. And increasingly, become crucial in the operation and maintenance of modern power systems. This technological change has brought new paradigms in the project of control, protection and supervisory systems of hydroelectric power plants, such as the use of distributed systems. The use of distributed architecture implies a drastic reduction of interfaces, simplified designs, flexibility in operation and maintenance and ease of future expansions. Thus, this conception leads to a reduction in the overall cost of projects. To implement this architecture in hydro power plants, it is proposed the integration of several IEDs and the use of highly reliable LANs with open protocols such as the ones defined in IEC 61850 and IEC 60870-5-101/-103/-104. This reflects the current state of the art in automation of hydro power plants.

Fig. 6.

Conversion from IEC 61850 data to a protocol that uses polling.

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As IEC 61850 enables client-server architecture, full use of object oriented approach, and other benefits outlined in this paper, the current trend is the increasing use this standard in new developments of the power an energy sector. However, the inability of DACUs and subsystems PLCs to communicate natively in this protocol is still a limiting factor. Additionally, the philosophy of distributed systems requires the professionals involved in the design, operation and maintenance of hydro power plants to absorb new knowledge and concepts. Although the controlled process is basically the same and the primary equipments do not change, there are huge modification in how they are integrated. More and more concepts like networking and parallel computing will be present in the day to day life of power engineers. Consequently, the consolidation of the use of distribution in the integration of control systems, automation and protection in power plants also depends on overcoming the technological and psychological challenges in the industry. Given the obvious benefits and the pressure for lower cost with better performance and functionality in the power sector, these are developments that will happen naturally in the coming years. R EFERENCES [1] MYRDA, P.; DONAHOE, K. The true vision of automation. IEEE Power & Energy Magazine, v. 5, n. 3, p. 32-44, May/June 2007. [2] HOSSENLOPP, L. Engineering perspectives on IEC 61850. IEEE Power & Energy Magazine, v. 5, n. 3, p. 45-50, May/June 2007. [3] MENDES, M. F.; JARDINI, J. A. Evoluça˜ o dos sistemas de automaça˜ o elétrica: caminhos das modernizaço˜ es de usinas hidrelétricas. In: ´ 13, 2009, Porto ERIAC - Encontro Regional Interamericano do CIGRE, Iguaçu. In Portuguese. In: Macmillan Dictionary. Available at: [4] INTEGRATION. http://www.macmillandictionary.com/dictionary/american/integration. Access in: Aug 22nd, 2010. [5] WACKER, G.; BILLINTON, R. Customer cost of electric service interruptions. Proceedings of the IEEE, v. 7, i. 6, p. 919-930, May/June 2007. [6] HOROWITZ, S. H.; PHADKE, A. G.; RENZ, B. A. The Future of Power Transmission. IEEE Power & Energy Magazine, v. 8, n. 2, p. 34-40, March/April 2010. [7] SANTACANA, E. et al. Getting Smart. IEEE Power & Energy Magazine, v. 8, n. 2, p. 41-48, March/April 2010. [8] JARDINI, J. A. Sistemas Digitais para Automaça˜ o da Geraça˜ o, Transmissão e Distribuiça˜ o de Energia Elétrica. 1 ed. São Paulo, 1996. In Portuguese. [9] BEHRENDT, K. C.; DOOD, M. J. Substation Relay Data and Communication. In: Annual Western Protective Relay Conference, 27, 1995, Spokane. [10] COULOURIS, G. F.; DOLLIMORE, J.; KINDBERG, T. Distributed Systems: Concepts and Design. 3 ed. Addison-Wesley, 2002. [11] International Electrotechnical Commission. IEC 60870-5-5: Telecontrol equipment and systems - Section 5: Basic application functions. Geneva, 1995. [12] International Electrotechnical Commission. IEC 61850: Communication networks and systems in substations - ALL PARTS. 1 ed. Geneva, 2010. [13] VYATKIN, V. et al. Towards intelligent Smart Grid devices with IEC 61850 Interoperability and IEC 61499 open control architecture. In: IEEE PES Transmission and Distribution Conference and Exposition, 2010, New Orleans. [14] SCHWARZ, K. IEC 61850 also outside the substation for the whole electrical power system. In: Power Systems Computation Conference, 15, 2005, Liege. [15] APOSTOLOV, A. Testing of complex IEC 61850 based substation automation systems. International Journal of Reliability and Safety, v. 2, n. 1-2, p.51-63, 2008.

Erick Fernando Alves (S’05, M’07) was born in S˝ao Paulo, Brazil in 1981. He received the E.E. bachelor with emphasis in Energy and Automation in 2007 from University of S˝ao Paulo. He joined the Systems Engineering Department of Voith Hydro S˝ao Paulo in 2005 as trainee. Since then, he worked in the control design of hydro power plants, specially with Excitation Systems and Speed Governors. Nowadays he is Lead Engineer of Excitation and Protection Systems at Voith Hydro S˝ao Paulo.

Masato Lucio Yano was born in Atibaia, Brazil in 1975. He graduated in E.E. with emphasis in Energy and Automation in 1998 from the University of S˝ao Paulo. Currently he is studying toward a M.B.A. in Getulio Vargas Foundation. He joint Siemens in 1998 as trainee, and the Excitation System group of Voith Siemens in 2002. Masato has held several professional positions in the group and was strongly involved with the development of Voith Hydro excitation systems, particularly leading the start-up of manufacturing in Brazil. Presently he is Manager of Automation Systems at Voith Hydro S˝ao Paulo. Marcus Hofmann was born in S˝ao Paulo, Brazil in 1972. He graduated in E.E. with emphasis in Power Systems in 1996 from Armando Alvares Penteado Foundation. Currently he is studying toward a M.B.A. in Getulio Vargas Foundation. He joined Voith Siemens in 2002 as a project engineer in Systems Engineering department. Since then, Marcus worked in the design of the various automation systems of hydro power plants, as well as in the development and standardization of these systems in Voith Hydro worldwide. He is the General Manager of Automation Systems at Voith Hydro S˝ao Paulo and Automation Systems Owner for the Voith Hydro group.