Analysis for the Improvement of IEC 61850 Based Substation Communications Using OPNET

With the increasing deployment of Distributed Energy Resources (DERs) in the distribution system, DERs presents many challenges for smooth and stable operation of the grid. For the effective management of DERs extensive communication between different components of DER and distribution system is required. To standardize the communication methods and modeling of logical nodes required for Intelligent Electronic Devices (IEDs) in DERs, data modeling of DERs is issued in IEC 61850-7-420 standard. This paper has contributed communication modeling of Green Energy Resources (GERs) and other DERs, modeling of messages exchanged among different IEDs with regard to their optimum structure & size and a Substation Communication Network (SCN) topology. End to End (ETE) time delay performance of the designed communication configuration architecture is presented using OPtimized Network Engineering Tool (OPNET). The dynamic performance result in the SCN has demonstrated the successful communication configuration for integrating the DERs in distribution system.

The International Electrotechnical Commission (IEC) 61850 standard describes the communication inside the substation automation system (SAS) setting the base for new interoperating devices that share information using the Ethernet network infrastructure. More recently, the request of time synchronization among SAS components for the timestamping of critical events or synchrophasor measurement has generated a very high interest in the IEC 61850 working group for distributed synchronization protocols like IEEE 1588. This paper analyzes the current situation, matching different implementations of the IEEE 1588, and their respective accuracy, with the requirements of typical SAS applications: from the millisecond synchronization accuracy required by fault recorder application to the microsecond required by the sampled values (SV). The main focus of this paper is on the integration of IEEE 1588 with real already existing systems, and the goal is the performance comparison of different architectures. For these reasons, experimental tests have been carried out using a real SAS network infrastructure [redundant gigabit optical fiber Ethernet network managed using rapid spanning tree protocol (RSTP)]. The results show that, under ideal conditions, the IEEE 1588 protocol can achieve synchronization accuracy slightly worse (80 ns) than legacy IRIG-B systems (15 ns). However, IEEE 1588 makes possible a great cabling reduction and a simplified maintenance when synchronization is directly transferred on the SAS system bus. On the other hand, experiments highlight that nodes connected through a legacy RSTP infrastructure, which does not support IEEE 1588 messages, can lose the time synchronization in the case of network traffic or reconfiguration of the network. Therefore, the integration of IEEE 1588 over existing IEC 61850 station bus is basically a tradeoff between installation costs and performance since it requires the replacement of already installed Ethernet infrastructure. In the last part, this paper analyses the challenges for the next SAS generation that has to combine on the same plants the high accuracy IEEE 1588 implementation with high-availability protocols based on IEC 62439. Since the lifetime of an SAS is more than ten years and the adoption of these technologies takes several years, some solutions that introduce synchronization and high-availability protocols guaranteeing compatibility with existing technologies have been analyzed, too. For instance, an adaptation block that (when attached to a high-availability network) reconstructs the interface signals (e.g., synchronization signals) required by traditional bay has been proposed.

High speed communication is critical in a digital substation from protection, control and automation perspectives. Although International Electro-technical Commission (IEC) 61850 standard has proven to be a reliable guide for the substation automation and communication systems, yet it has few shortcomings in offering redundancies in the protection architecture, which has been addressed better in IEC 62439-3 standard encompassing Parallel Redundancy Protocol (PRP) and High-availability Seamless Redundancy (HSR). Due to single port failure, data losses and interoperability issues related to multi-vendor equipment, IEC working committee had to look beyond IEC 61850 standard. The enhanced features in a Doubly Attached Node components based on IEC 62439-3 provides redundancy in protection having two active frames circulating data packets in the ring. These frames send out copies in the ring and should one of the frame is lost, the other copy manages to reach the destination node via an alternate path, ensuring flawless data transfer at a significant faster speed using multi-vendor equipment and fault resilient circuits. The PRP and HSR topologies provides higher performance in a digitally protected substation and promise better future over the IEC 61850 standard due to its faster processing capabilities, increased availability and minimum delay in data packet transfer and wireless communication in the network. This paper exhibits the performance of PRP and HSR topologies focusing on the redundancy achievement within the network and at the end nodes of a station bus ring architecture, based on IEC 62439-3.

Substation communication network (SCN) provides real-time, high-speed, and reliable data transmissions for the advanced monitoring and control functionalities, which are facing increasing cyberspace threats and attacks. Efficient threat perception and cyber situational awareness are essential to enhance secure and reliable SCN operations. This article explores multiscale SCN traffic pattern characteristics with holistic network traffic, separated network traffic for included devices (especially IoT devices) and separated network traffic of certain types of protocol. The proposed online traffic-oriented SCN traffic anomaly detection and cyber situational awareness models are designed for the network anomalies and cyber-attacks that could cause network traffic pattern variations. We leverage a fractional autoregressive integration moving average (FARIMA)-based dynamic threshold model to detect abnormal traffic patterns without sophisticated computations or deep packet inspection. The SCN real-time operation conditions are timely quantified through the statistical methods with the alliance of SCN topology and protocols. The cyber situational awareness model is further carried out to evaluate the most affected protocol and security risks of various devices in SCN using Grubbs’ test. The experiment results are carried out based on a real 110-kV intelligent power substation. The numerical results confirm the comparative low mean square error (MSE) and low complexity of the online traffic characterization when forecasting holistic network traffic and separated network traffics. Furthermore, the timely and quantified cybersecurity risk analysis is conducted based on the SCN traffic with varying scales to detect cyberspace threats and identify the high-risk SCN devices and the most affected protocol.

Interoperability tests and plugfest events provide an environment to test and assure interoperability of power grid devices - to ultimately achieve equipment plug and play. However, interoperability analysis is very time-consuming and error-prone since tasks must process tens of gigabytes (GBs) of network packet data. Therefore, the challenge we face is how to efficiently analyze interoperability. To address this challenge, the National Institute of Standards and Technology (NIST) has developed an interoperability analysis tool for International Electrotechnical Commission (IEC) 61850-9-2 standard-based merging units (MUs). This paper introduces a software tool that can parse IEC 61850-9-2 packet data from a packet description markup language (PDML) file and automatically analyze the interoperability of IEC 61850-9-2 sampled value (SV) messages based on the IEC 61850-9-2:2011 protocol. The interoperability analysis includes data analysis of the media access control (MAC) layer, link layer, and application layer of IEC 61850-9-2 SV messages. This tool has successfully been used to analyze nineteen sets of IEC 61850-9-2 SV messages collected from both commercial physical and simulated MUs provided by seven vendors at the 2017 Utilities Communications Architecture International User Group (UCAIug) IEC 61850 Interoperability (lOP) Testing and Plugfest event.

In this chapter, we will adopt the analog erasure model to describe the communication channel present inside a control loop. This model, also referred to as the packet erasure or packet loss model, can be described as follows [8]. The channel operates in discrete time steps. At every time step, the channel accepts as input a finite dimensional real vector r(k). The value of the output of the channel y(k) is chosen according to an erasure process. At every time step, the erasure process assumes either the value T or the value R. If the value at time k is T , y(k + 1) = r(k) and a successful transmission is said to have occurred. Otherwise, y(k + 1) = φ and an erasure event, or a packet loss, is said to have occurred at time k. The symbol φ denotes that the receiver does not receive any data; however, the receiver is aware that an erasure event has occurred at that time. Note that we have assumed that the channel introduces a constant delay of one time step. The analog erasure model aims to capture the data loss effect due to a communication channel. Due to effects such as interference and fading in wireless channels, congestion in shared networks, or even overload and interrupts at a micro-controller, various parts of a control loop between the sensor and controller, or the controller and actuator, may exhibit information loss. By considering the idealization in which every successful transmission results in the communication of a real vector of a bounded dimension, such situations can be modeled using an analog erasure representation. While an analog erasure model has an infinite capacity in an information theoretic sense, it is often a useful representation for the cases when the communication protocols allow for large data packets to be transmitted at every time step. For instance, the minimum size of an ethernet data packet is 72 bytes. This is much more space for carrying information than usually required inside a control loop. If the data packets allow for transmission of control and sensing data to a high fidelity, the quantization effects are often ignored and an analog erasure model adopted. Various descriptions of the erasure process are possible. The following two models are the most popular:

The fast real-time application message is an object-oriented substation event—GOOSE (Generic Object Oriented Substation Event). It mainly works on the process layers and bay layers of digital substation. GOOSE intelligent substation communication network can realize the key function of the overall intelligent sub- station functions. This paper will make a systematic analysis of GOOSE. At first, it will provide a detailed analy- sis of the transmission mechanism and process of GOOSE message. As certain practical operability lacks the actual application of the multicast filtering method which is applied to GOOSE message based on IEC61850 standard, this paper will summarize three message filtering methods, compare the advantages and disadvantages in topological networks of different kinds in accordance with the instantaneity of GOOSE intelligent substation communication network and draw a conclusion that the independent configuration scheme of GOOSE and SV can adapt to the requirement of times, so as to provide theoretical references for the selection of practical intelli- gent substation communication network in the future.

智能变电站在电力系统中处于重要地位，为了满足电力系统的要求，电力通信网结构不断地进行优化，大量引进通信领域新技术，使得电力通信网越来越复杂。影响变电站通信安全的因素日益增加，变电站通信网络安全这一问题变的日益复杂。本文以智能变电站的通信网络为基础，对智能变电站通信网络的发展历程进行简要介绍，分析比较几种通信技术的优缺点，针对变电站信息安全面对的威胁以及现阶段管理现状、管理制度等在实际运行中存在的问题进行深入讨论，全面研究分析了变电站面临的信息安全问题。 Intelligent Substation in the power system is an important factor. In order to meet the power system require- ments, the system constantly optimizes power communication network structures, including massive introduction of new communications technologies, making electric power communication network more complex than ever. Factors affecting the substation communication safety are increasing. Substation communication network security problems become more complex. In this paper, intelligent substation communication networks based on intelligent substation communication network development process are briefly described, and the advantages and disadvantages of several communication technologies are analyzed and compared . In the end of the article, this paper comprehensive analyzed substation informa- tion system threats, present management situation and management system in actual operation.

The main purpose of this paper is to study the communication protocol IEC61850 (Communication Networks and Systems in Substations) to develop of practical fast transmission modes in direct trip schemes, using communication functions to implement protection, control and condition monitoring functions under IEC61850 protocol to complete devices data integration in substation automation system. The way of direct trip schemes can provide fast communication speed to stable power system operation in case of suddenly events occasions. The messages interchange via GOOSE (Generic Object Oriented Substation Event) application is based on the IEC61850 communication protocol to implement fast direct trip modes. It is found that the interaction communication of direct trip schemes among various protective relays can be achieved by the IEC61850 protocol based on GOOSE application to approach system stabile operation under occasionally events.

Communication network is the infrastructure of intelligent substation in smart grid, and it plays a vital role in substation automation system (SAS). The traditional Ethernet network cannot fulfill the requirements of SAS, and these requirements consist of centralized network management and control, dynamic resource allocation flow. In this paper, Software Defined Network (SDN) is used to manage and control the communication network of SAS. Based on SDN and IEC61850, firstly, shortcoming of current SAS network management is illustrated. Then, some new features about SAS have been designed, such as realization principle, application technology, function modules and workflows of network management. Finally, simulation experiments are designed to verify network management function. The simulation results validate the effectiveness of dynamic and real-time supervision in SAS communication network.

The Distributed Coordination Function (DCF) is the fundamental access method defined in the IEEE 802.11 Standard for Wireless Local Area Networks (WLANs). With this standard, the Access Point (AP) and the mobile stations consume a significant amount of energy to contend for access to the shared wireless channel. In order to improve the energy efficiency of WLANs, we investigate in this paper a simple and backwards compatible mechanism, called Bi-Directional DCF (BD-DCF), that enables bidirectional communications between wireless stations with a single channel access invocation. The key idea is to let the AP or any mobile station transmit a data packet together with the acknowledgement upon the successful reception of a data packet. This approach reduces the communication overhead, the channel contention, and better balances uplink and downlink transmission opportunities. We evaluate the performance of the proposed BD-DCF by means of computer-based simulation considering different traffic loads, degrees of traffic symmetry, data packet sizes, and data rates. The results presented in this paper show that the BD-DCF protocol can improve the energy efficiency of DCF up to 50%.

Cloud computing, which is claimed to provide plentiful storage, computational, and other resources, has become a promising platform to support resource-intensive applications. Due to the wide adoption of smart things to support domain applications and considering the delay-sensitivity of certain requests and limited network capacity compared with huge data packets to be transmitted, the quality of experience (QoE) may be hard to be satisfied when requests are solely supported by cloud computing. In this setting, edge computing has become an infrastructure to facilitate request satisfaction at the network edge. This article proposes a mechanism to optimize the collaboration of heterogeneous edge servers with certain QoE constraints. Specifically, concurrent requests, which are usually represented in terms of SQL queries, are rewritten as atomic queries, and these atomic queries are optimally assigned to edge servers through adopting an algorithm inspired by the minimum spanning tree, where QoE factors, including the delay, size of data packets, and number of operators, are considered. Evaluation results indicate that the proposed mechanism can effectively improve the QoE of requests compared with the state-of-the-art’s mechanisms.

CORBA-BASED INTEROPERATION IN SUBSTATION AUTOMATION SYSTEMS

In this paper, we describe a packet data size minimization method designed specifically for advertising and discovery in ubiquitous networks. The minimization is effective for achieving superior discovery performance characteristics such as discovery time and power consumption. The proposed method for data packet size minimization is based on indexing of advertisement text. In the method, dictionaries and indexed data are stored separately, i.e. dictionaries are stored on a server and indexed data is stored on ubiquitous wireless devices, and the same dictionaries are shared among all users. We evaluate an average packet data size and dictionary size for three indexing methods: regular indexing, category indexing and attribute indexing; and show that these methods achieve data packet sizes which are about two and three times smaller than raw data packets and zipped packet data sizes respectively. Also, we show that category indexing allows users to be less dependent on the infrastructure.

This paper compares the performance of two time-division multiplexed media access protocols designed for star-coupled wavelength-division multiplexed (WDM) photonic networks. The TDMA-C protocol is reservation based: one WDM channel is used to reserve access for data packet transmission on the remaining data channels. Control channel access arbitration is achieved through time-division multiplexing, enabling all active nodes the opportunity to transmit once every control cycle. This approach significantly reduces the long synchronization delays typical of time-division multiplexing systems since the control cycle length is proportional to the control packet size rather than the data packet size. Every node in this system has one turnable transmitter and two receivers. >