A Smart Grid is an electrical grid that uses information & communications technology to gather and act on information. According to the European Technology Platform, a Smart Grid is an electricity network that can intelligently integrate the actions of all users connected to it – generators, consumers and those that do both ‘Prosumers’ – in order to efficiently deliver sustainable, economic and secure electricity supplies. According to the US Department of Energy, the smart grid is self-healing grid, enables active participation of consumers, operates resiliently against attack and natural disasters, accommodates all generation and storage options, enables introduction of new products, services and markets, optimizes asset utilization and operates efficiently, and provides reliable and high quality power for the digital economy. Smart grid combines advanced telecommunications and information technology applications with ‘smart’ appliances to enhance energy efficiency on the electricity power grid as shown in Fig. 1. Power system or smart grid automation includes processes and technologies associated with the generation, transmission, distribution and utilization that generate electricity, transmit and distributes it for end user applications and needs. Grid automation can be further classified into generation automation, transmission automation & substation automation/distribution automation blocks making it more decentralized in order to focus more on corresponding sector applications and meet its own challenges. More details about each automation block are explained in further sections. Initially when every vendor used to have their own proprietary technologies for automating the systems were non-interoperable & hence need for standards & standardization has evolved.
Fig. 1: Smart Grid Framework
Smart Grid Automation
Automating a power system or grid can bring substantial benefits to the operators and end-users by improving system reliability, planning, design, efficiency and response to various failure modes that may occur during day-to-day operations, which matches with some of the smart grid objectives. The availability of technology for automation has grown significantly over the past few years. Several challenges led to the birth of power system automation of which system growth, availability, reliability, engineering, planning expectations and most importantly smart grids are the key ones. As the system growth continues and expectations rise due to the tremendous growth of industrial and commercial consumers, it will demand even further automation of the system. As automation research engineers, we realize that the counterweight to implement technology on automation is the high cost which includes design, installation, equipment and maintenance. To accomplish this deciding the communications protocol and interoperability between various nodes plays a vital role. Hence there is a need of standardized automation systems which can communicate and operate on a standard protocol and design framework. Grid automation across the network can be further classified as combination of generation, transmission, substation and distribution automation blocks.
Many power system networks have adapted available technology for various benefits, apart from these hardware and software technology requirements for building automation, the other major consideration in developing automation network is ongoing need for human operators to continue in maintaining and extending the automation network, as per requirements and operations listed in Tables 1 & 2, into the future as once the benefits of automations are realized by the execution side of power system or grid, there will be a demand to automate the entire existing system and any new devices added in the future, to be a smarter grid.
Smart Grid Automation Standardization
Smart grid objectives can be realized to a greater extent by grid automation, but major benefit of incorporating these automation technologies can only be realized by automation along with standardization. List of IEC standards relevant to smart grid automation as in Fig. 2 are-
- IEC 62270 – Power plant Automation
- IEC 61158 – Foundation Field Bus Automation
- IEC 61499 – Distributed Control & Automation
- IEC 62357 – Power system control and communications
- IEC 62351 – Power system security analysis
- IEC 61970 – Energy Management Systems
- IEC 61850 – Substation/Distribution Automation
- IEC 61968 – Distribution Management Systems
- IEC 61334 – DA power line communications
- IEC 62056 – Energy Metering Automation
Fig. 2: Smart Grid Automation Standards
Smart Grid Automation and Standardization Analysis
In this section we shall broadly review various recent trends in Power System Automation for each of the individual automation blocks as shown in Fig. 3 (generation, transmission, substation & distribution) that helps in meeting some of the smart gird objectives.
Fig. 3: Grid Automation Network View
Generation Automation and Standardization
The automation controller (IEC 62270) in the Instrumentation & Control panel of power plant is a major component. Since the generation and demand should match for better operation of the grid and since it is not possible to store excess power or generate instantly more power, these controllers played a key role in automation for a fail-safe mode of operation in which the following functions are controlled automatically; Stress on turbine during startup & shutdown, Grid synchronization, Controlling the loading of turbine and generator, frequency stabilization to avoid penalties, managing plant load requirements apart from external load, Prevention of overloading of turbine & compressor unit, Protection and control against faults and possible failure modes. Embedded systems platform forms heart of control systems. Use of advanced communication technologies in a highly integrated control environment has drastically improved the performance of control systems.
The distributed platform (IEC 61499) as realized by incorporating various logical control nodes (LCN) which computes their own algorithms without the need of any central node for functioning, offers wide variety of flexibility in plant control and automation. These algorithms are realized by a set of equations governing the operation of a specific logical node. After its successful implementation and operation in substation automation, IEC 61850 standards have been attracted by generation automation engineers to realize protection, control and automation functions in a power plant. IEC 61850 GOOSE messaging and necessary logic programming on protective relay IEDs has resulted in higher performance with more data to monitor and troubleshoot the issues in real time. Such applications of configurable GOOSE messages are, to reserve interlocking or reverse blocking, breaker failure protection, high voltage direct transfer trip and load shed/transfer, while the traditional advantages of GOOSE such as reducing the amount of copper wire and relays necessary for protection is well acknowledged. Also, custom defined object oriented models of IEC 61850 helped in realizing various logical node operations.
Later, Foundation field buses (IEC 61158) being the digital serial two-way communication system for plant or factory automation after successful implementation in the process industries has attracted power plant engineers to use it. Its targeted applications based on regulatory control offer discrete control & automation. With the advent of advanced software technologies, it seems that web based control mechanisms are well suitable for automation environments like SCADA to certain extent like monitoring functionality but the need to provide direct access to automation system parameters will set limitations. These advanced software based HMI’s helps in viewing the exact field conditions by means of animations, 3D visualization and different coloring schemes for differentiating different types of faults for the critical plant equipment.
Transmission Automation & Standardization
As the power systems becoming large and exhibiting increasingly complex nature, there is a need for advanced measurement technology, tools, data analytics and operational infrastructure that facilitates the better automation, control and management of complex power system. Such system is called as Wide Area measurement System (WAMS) which uses advanced satellite based time synchronization technology for complete monitoring, protection and control of the power system. Though Energy Management Systems (IEC 61970) and SCADA (IEC 62357) were available predominantly from quiet long time performing operations like state estimation, optimal power flow, security analysis, contingency analysis, stability analysis etc. The present trend in automation in this area are automatically scheduling inter-area power exchange, computing online power transactions, handling deregulated and restructured power system operations, allocating costs to various generating participants, monitoring system security against possible physical and cyber-attacks, wide area stability analysis, state estimation based on WAMS, optimal bus load shedding based on critical bus synchronism lost etc. Security assessment, shown in Fig. 4, through WAMS is an important outcome of Smart Grid automation as it helps in performing real time operation and decision making. The power electronic based systems offering control of AC transmission parameters for enhancing stability and increasing power transfer capability were traditionally based on series and shunt compensation devices. FACTS has now become much more robust in control due to the accurate and timely measurement of reference parameters. Communication has been added to these FACTS devices which made it interoperable with remote control operations based on WAMS. The present trend in automation is to automatically control transient stability of the line, damping of the system, voltage stability, sub-synchronous resonance, short-circuit current levels, integration of wind power generation to the grid & terminal performance of HVDC converter using the FACTS based device.
Fig. 4: Security assessment using WAMS data (Source: CRIEPI)
Today’s Energy Management Systems and SCADA systems are predominantly based on Local Area Network (LAN) and Wide Area Network (WAN) communications. Multivendor protection, control and monitoring IEDs integrated with various control centers or gateways at substation carry information to a central control center. Hence methods for information security to assure privacy of data and information, integrity of data and commands from control centers and authentication of the source of receiving data and commands play a critical role (IEC 62351). In the present trend, automated security systems that complement the existing SCADA system, performs the intruder detection for possible physical & cyber-attacks based on a set of protocols and executes data integrity based algorithms using the knowledge of power system components, control actions to differentiate authentic and false trip commands due to malware. Cyber Security indeed is required for all automation blocks.
Substation Automation & Standardization
Earlier when protection devices were based on electro-mechanical technology with hard-wired communication they offered some limitations in terms of speed and operation. They were slowly replaced with micro-controller based devices which increased the speed of operation. With the advent of advanced micro-controllers today the diversification and complexity of functions required by automation becomes a strong trend of evolution. IEC 61850 standard for substation automation has totally revolutionized the power delivery industry since its introduction in 2005 time frame. The major breakthrough happened with the realization of “Interoperability” between multi-vendor IEDs. 61850 also offer easier configuration, standardized logical nodes and functions for every equipment, high-speed Ethernet communications on station bus, and peer-peer communications called GOOSE, enhanced security controls, predefined XML file formats etc. Initially IEC 61850 Substation automation was focused on operations and control within a substation, later the same has been extended to feeder automation by a virtual extension of SAS having built-in intelligence in IED along with high speed communications and controls (Fig. 5) Feeder automation can be realized in a centralized or decentralized approach based on number of feeders covered.
Fig. 5: IEC 61850 based SA system
The automation and control of the current electric power systems based on the SCADA model though provides adequate reliability and speed of operation it does not offer flexibility in terms of open access to information. Due to the intrinsic distributed nature of power systems, multi-agents based technology can provide greater autonomy for each component in power system. In present trend, agents play key and distinct roles in monitoring and control, communication by means of messages, information retrieval through mobile based agents travelling over the network and interaction between agents for specific tasks.
The substation secondary equipment such as sensors, transducers etc, measures various analog parameters like voltage, current, temperature and transfers to main relay using hard-wired cables. When it comes to replacement and maintenance of substation secondary equipment’s, it may impact the overall substation availability because of complex wiring and relay obsolescence. To overcome this problem IEC 61850 has introduced process bus which is similar to field bus in generation plant, where in a standardized Ethernet bus is used to provide interfaces to primary equipment. A merging unit (MU) collects all the data from field sensors in a synchronized manner, digitizes the signals and transfers the sample values automatically on high speed Ethernet or process bus (1Gbps) to the subscribed primary equipment’s. This helps in reducing maintenance cost and time for re-configurations. IEEE 1588 precision time protocol (PTP) over SNTP made even 20ms time period wave analysis possible today and multiple IEDs to look at same zone using these accurate time measurements increasing reliability of protection.
Distribution Automation & Standardization
While there is an overlap between the substation and distribution automation, based on IEC 61850 the main aims of the distribution automation system being Supervisory Control and Data Acquisition (SCADA), Volt & Var Control (VVC), Fault Location (FL), Feeder Reconfiguration (FR) (Self-Healing), FLISR (Fault Location, Isolation, and Service Restoration), which is a hybrid of FL and FR. It is far possible to realize automation without communication which offers remote monitoring and control of the distribution system. Though there are only one TCP based protocol being used for communications from generation to substation automation, however distribution automation is being realized on a wide variety of communication types like PLC (IEC 61334), Ethernet, RS 485, wireless, 3G, CDMA, WI-Max, Zigbee, GPRS, GSM etc, the reason being distribution closer to end users who use these communications often in day-to-day life. The AMI systems, usually collect data from various smart meters in the field in an automated manner using DLMS/COSEM (IEC 62056) standard specification and transfer it to a central location called Meter Data Management System (MDMS). AMI network offers low-bandwidth two-way communication links between meters & back office.
Fig. 6: Distribution Automation and AMI
With the evolution of a variety of energy resources like solar, wind etc, apart from regularly used natural resources for power generation led to the formation of Micro-Grids, which can operate in synchronization with grid or in an isolated mode during an outage of the grid, supplying power to local load in a distributed manner to fill the supply and demand gap during peak loading conditions on the grid. When the micro-grid is operating in islanding mode and when the demand increases beyond its supply, it may lead to grid collapse; hence automation of micro-grid environment is a key for smart grid.
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