Hyo-Sik Yang

A survey of communication network paradigms for substation automation

In the realm of substation automation (SA), communication infrastructure plays a vital role in mediating between physical and virtual worlds of substation. Specification of data exchanges through standardized communication stacks is therefore an important issue for all substation equipment manufacturers seeking to provide vendor interoperability. Nowadays competitive electric utility marketplace, reliable and real-time information become the key factor for reliable delivery of power to the end- users, profitability of the electric utility and customer satisfaction. The operational and commercial demands of electric utilities require a high-performance data communication network that supports both existing functionalities and future operational requirements. As communication arena is changing day by day, the need for efficient and reliable communication infrastructure to address SA is evident. In this respect, a communication network constitutes the core of the SA, thus the design of cost-effective and reliable network architecture is a crucial task. Most of the existing communication networks claim to address the need of communication architecture for SA but in some regard these claims just could not fulfill the constraints imposed by highly available environment for SA. This paper presents a survey and analysis of the current state-of-the-art communication infrastructure in the SA. As Ethernet technology becomes more reliable and also widely available with fiber optical communication so this paper also examines the key issues and requirements for Ethernet in the substation environment and also opens some research challenges.

DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation

This paper describes operational analysis results of the DC micro-grid using detailed model of distributed generation. Detailed model of wind power generation, photo-voltaic generation, fuel cells generation was implemented with the user-defined model of PSCAD/EMTDC software that is coded with C-language. The operation analysis was carried out using PSCAD/EMTDC software, in which the power circuit is implemented by built-in model and the controller is modeled by user-defined model that is also coded with C-language. Various simulation results confirm that the DC micro-grid can operate without any problem in both the grid-tied mode and the islanded mode. The operational analysis result confirms that the DC micro-grid make it feasible to provide power to the load stably. And it can be utilized to develop an actual system design and building.

Optimized Security Algorithm for IEC 61850 based Power Utility System

As power grids are integrated into one big umbrella (i.e., Smart Grid), communication network plays a key role in reliable and stable operation of power grids. For successful operation of smart grid, interoperability and security issues must be resolved. Security means providing network system integrity, authentication, and confidentiality service. For a cyber-attack to a power grid system, which may jeopardize the national security, vulnerability of communication infrastructure has a serious impact on the power grid network. While security aspects of power grid network have been studied much, security mechanisms are rarely adopted in power gird communication network. For security issues, strict timing requirements are defined in IEC 61850 for mission critical messages (i.e., GOOSE). In this paper, we apply security algorithms (i.e., MD-5, SHA-1, and RSA) and measure their processing time and transmission delay of secured mission critical messages. The results show the algorithms satisfying the timing requirements defined in IEC 61850 and we observer the algorithm that is optimal for secure communication of mission critical messages. Numerical analysis shows that SHA-1 is preferable for secure GOOSE message sending.

QVT-Based Model Transformation to Support Unification of IEC 61850 and IEC 61970

A smart grid is an electrical power grid infrastructure for improved efficiency, reliability, and safety based on automated monitoring and control of data and communication. IEC 61850 and IEC 61970 are core standards in the smart-grid domain for substation automation and power operation management. There are significant data exchanges involved between the IEC 61850 level and the IEC 61970 level, which require high compatibility between the two standards. However, due to different perspectives and independent evolution, IEC 61850 and IEC 61870 are not compatible and practitioners have to come up with their own data mapping for the standards in an ad-hoc manner. This has led to significant issues on interoperability and data consistency in smart grids. An effective solution for this is to define a common semantic model of the standards and provide a systematic transformation method for transforming a model of the standards to a model of the common semantic model. In this paper, we present a metamodeling approach for unifying IEC 61850 and IEC 61970 and transforming models using query/view/transformation (QVT). We demonstrate the approach using a power transformer example.

Latency and Traffic Reduction for Process-Level Network in Smart Substation Based on High-Availability Seamless Redundancy

Process-level communication network brings digital technology to the high-voltage switchyard, a major stage in the evolution to ensure the protection control and data acquisition of smart substation. This network requires a mission-critical protocol such as high-availability seamless redundancy (HSR). Two main drawbacks of HSR, however, are the transmission latency introduced by each hop in the single ring (SR) topology and the unnecessary traffic due to the duplicated copies of sending frames. This study presents two enhanced solutions and fully implements quick removing (QR) approach to HSR for improving the latency and reducing the traffic volume in process-level network. The main idea of these two enhanced solutions is to reduce the minimum number of hops required for delivery messages to destinations for reducing the maximum end-to-end latency (ML). To achieve traffic reduction, the QR approach is concretized in HSR nodes for fully applying to any closed-loop HSR networks. Performance of IEC 61850-based process bus networks are analyzed theoretically and demonstratively by Network Simulator-2 (NS-2) and OPNET Modeler®. The combination of enhanced solutions and the QR algorithm solves both main drawbacks of HSR, improving the network performance optimally. These enhancements of HSR are applicable to not only on substation automation networks, but also to any real-time industrial networks.

Role-based access control for substation automation systems using XACML

There has been an increasing need for accessing data of internal equipment and devices of a substation system from external systems as power grids evolve. This has also introduced growing concerns on data security. In response to the concerns, IEC 62351 has proposed role-based access control (RBAC) for substation automation. In this work, we present a novel approach for implementing RBAC based on IEC 62351 for substation automation using eXtensible Access Control Markup Language (XACML). We integrate the approach with IEC 61850 by extending Abstract Communication Service Interface (ACSI), Manufacturing Message Specification (MMS), and System Configuration Language (SCL). A major advantage of the approach is that it fully conforms to both IEC 61850 and IEC 62351 and highly compatible with SCL as both XACML and SCL are XML-based. We implement the approach using OpenIEC61850 which is an open source library for ACSI services and demonstrate the implementation.

Baseline efficiency in EPON based architecture to inter-network substations

The design of cost-effective, interoperable, and efficient communication architecture is indeed one of the pressing needs not only for the realization of substation automation (SA) as per specification of IEC61850 but also to inter-connect different substations with minimum cost to bring data from all substations on the single information highway thereby paving a smooth way to centralize all the available information. Ethernet technology has dramatically changed the communication trend because of its availability, efficiency, cost effectiveness, proven interoperability, and capability to drive on-demand bandwidth as per incremental growth and expansion of the network and on the other hand optical fiber communication system is one of the technically attractive communication medium due to its high capacity, efficiency, and security. Therefore, EPON (Ethernet Passive Optical Network) is the desired communication paradigm for the SA as it is shipped with the two most demanding communication trends, i.e., Ethernet and Fiber Optics in a single package. EPON underscores the importance of not only last-mile operability for inter-connecting different substations but can also play a vital role when ATM is replaced with GPON (Gigabit Passive Optical Network) for the long-haul communication thereby saving the cost of protocol conversion. In this paper we propose EPON as the desired communication architecture for inter-connecting substations and present analysis related to the significant importance of EPON with respect to the deployment in the substation environment both internally and externally. Finally we show the result of simulations to validate the deployment and effectiveness of our purposed communication paradigm for substation.

Model transformation between OPC UA and UML

OPC Unified Architecture (UA) is a platform-independent standard for message-based communication between clients and servers on various types of network to facilitate information exchange. OPC UA has been adopted in various domains such as power grids, building automation, and smart devices to support interoperability of involved systems. These domains also use Unified Modeling Language (UML) as the standard notation for data modeling or system modeling. Use of two different notations in the same domain causes compatibility issues. To address this, we present an approach for transforming OPC UA to UML to improve their compatibility and integration. In the approach, we rigorously analyze the semantics of OPC UA elements and establish a mapping between OPC UA elements and UML elements based on the analysis. Based on the mapping, we define transformation algorithms using Query/View/Transformation (QVT) which is a standard model transformation language by OMG. We demonstrate the approach using case examples in the power grid, building automation, and smart device domains. HighlightsOPC UA and UML are analyzed for correspondence.Mappings are established between OPC UA elements and UML elements.Based on the mappings, transformation rules are defined in QVT.Three case examples are presented demonstrating transformation.

An improved High-availability Seamless Redundancy (HSR) for dependable Substation Automation System

High-availability Seamless Redundancy (HSR) is an emerging standard that is suitable for mission-critical communication of IEC 61850 based Substation Automation System in smart grid, where the dependability is very important. This redundancy protocol provides zero recovery time by offering duplicated frames for separate physical paths, but it generates and circulates unnecessary traffic inside the network that will degrade the performance of the network and may cause the congestion, delay, or frame loss. To improve the HSR network performance, the main drawback of generating extra traffic should be considered and eliminated. This paper demonstrates comprehensive performance analysis of IEC 61850 based substation automation networks and applies the quick removing (QR) algorithm to improve the performance of the HSR network to overcome the major drawback. The performance analysis includes the HSR modules, i.e., Doubly Attached Node for HSR (DANH), Redundancy Box (RedBox), and Quadruple Box (QuadBox), and IEC 61850 services, i.e., Generic Object Oriented Substation Events (GOOSE), Sampled Measurement Values (SMV), and report service. Performance analysis was conducted to verify the timing constraints described in IEC 61850 as a reference for designing proper HSR network topology. The numerical results show that the frame loss, restricted in mission-critical network, occurs due to large amount of traffic volume, which is the main drawback of HSR. The QR algorithm improves the traffic performance of HSR by reducing the unnecessary traffic along with the decrease of packet loss significantly.

Communication Networks for Interoperability and Reliable Service in Substation Automation System

The IEC 61850 presents the international standard for communication networks and systems in substations. The standard discusses the detail of the requirements and the architecture of substation automation system as well as data type and format. The TEC 61850 will substitute the traditional hardwired analog communication network using up- to-date communication protocols for interoperability and reliable service. Basically all IEDs are connected through TCP/UDP and IP over Ethernet based LAN to exchange data. Thanks to the Ethernet frame, we can deploy any type of advanced communication technology for communication in substation. This paper discusses the technical issues associated with the communication networks integration in detail. We consider the possible topologies in Ethernet architecture with the topic in the discussion of the pros and cons of their architecture, and the required functionality of each network elements in detail. Several data types, e.g., GOOSE, time synchronization, and FTP, which uses different protocol stack, are used in substation system with their own delay requirements. Communication profiles for these services are discussed in this paper. We also present the system configuration, requirements, and architecture of the system. We establish a guideline to build a communication networks in substation automation system based on IEC 61850 and presents the ad-hoc based architecture for survivable substation automation system.