The Role of Modern Substation Automation Systems in Smart Grid Evolution
Written by Ahmed Altaher
Modern substation automation systems (SAS) play a vital role in modernization of power grids. These systems benefit from stable evolutions of standards such as the IEC 61850 and its parts. Technical Committee 57 (TC57) of the International Electro-technical Commission (IEC) has released this standard to enforce interoperability between substation devices, e.g. Intelligent Electronic Devices (IEDs), and to enable abstraction of communication services . It provides vertical and horizontal communications between devices and equipment in three levels: station, bay and process (Fig. 1).
Figure 1. The hierarchy of a substation system with IEC 61850 in three levels
Advantages of Modern SAS
The IEC 61850 standard enables many features such as interoperability, seamless communication networks, object-oriented design, systematic factory and site acceptance testing. IEDs manufacturers add several functions to use these features and to exchange data with upper levels, e.g. station level. Clearly, the standard adopts many Information and Communications Technology (ICT) principles to improve SAS functionalities at station, bay and process levels. Hence, modern SAS features bring smartness to substations to allow data collection and processing in real-time, and to enable flexible design of protection schemes. The digital exchange of data, between substation devices and equipment through Ethernet networks, enables bay level devices to make decisions in real-time, while processing of the collected data shall provide useful information for station control room, control centers and the other grid parts.
The software based intelligent devices with object modeling can deliver high reliable functionalities for technicians and engineering in every phase of the substation life cycle. For instance, at the design phase, engineers can use objects to build protection and measurement functions through object-oriented applications. These objects can represent bay (e.g. protection relay status), process and switchyard equipment (e.g. circuit breaker status). Additionally, contents of non-centralized human machine interface (HMI) screens can be designed with flexible usage of these objects (Fig. 2).
Figure 2. Design of HMI interfacing by using logical nodes within intelligent electronic devices and merging units
The figure shows some logical nodes for switching, control and measurement functions. Table 1 illustrates these logical nodes, i.e. used in many devices in the figure. The concept of object modeling provides flexibility for designing and implementing many functionalities inside SAS intelligent devices.
Table 1. Logical Nodes that are used within many devices such as IEDs and MUs
Benefits for the Smart Grid
The smart grid can use SAS features to rapidly deploy several services and functions in transmission and distribution networks and control centers. One function can be to protect a network of connected renewable energy resources. Hence, the grid becomes scalable with these new SAS functionalities. The following points highlight most important benefits for the smart grid evolution:
Availability of Massive Data for Measurement and Metering
With modern SAS systems, availability of digital measurement and metering helps to provide precise information about the grid status when these parameters are collected in regional or national level. Availability of substations status data can also help to connect or disconnect any resource of energy according to demand-response scheme. Sampled Values (SV) service carries analogue measurements values in digital form and SV can transmit digital instrumentation measurements embedded into multicast Ethernet frames, such as current and voltage to SAS devices. A good example for this communication service is to send data with a certain sample rate, e.g. 80 samples/cycle in 50 or 60 Hz cycle. According to the standard, protection, automation and coordination must respect time-critical constraints to enhance reliability, e.g. precise time synchronization of this sampling mechanism in order to avoid safety issues .
Availability of Data for Maintenance
The maintenance of the grid shall benefit from modern substations data as the later forms an important source of failure data. For instance, the IEC 61850 object models provide datasets that contain status of equipment at many levels in the substation. Generic Object-Oriented Substation Events (GOOSE), defined within the IEC61850 part 7-1, are high-speed messages to deliver status and event changes. GOOSE datasets are embedded into Ethernet frames that have priority tagging capability to improve time-critical priority demands. These messages can be routed outside the substation to provide useful information for maintenance planning and follow-ups. These datasets help to schedule preventive maintenance policies and to extend the life of grid assets (e.g. transformers and capacitors). Another important datasets are the communication network and interfaces status that can help to diagnose failures and distinguish between cyber and physical ones. Testing can be achieved with these datasets as well as automatic diagnostics shall help reveal hidden failures .
Estimation of the Overall Grid Status
Regionally collected data from modern smart substations, through the routed messages (routed GOOSE and SV), can help to manage protection and control strategies in real time with large power grids. The overall state of the grid therefore can be estimated before appearance of reliability issues, such as cascaded failure or blackouts. In addition, grid expansion can be planned seamlessly using status data from SAS.
Digital Information for Reliable Power Service
The digital sampling-related parts, of the IEC 61850 standard, provide recommended sampling rates in order to draw a useful shape of the grid. These samples represent frequency, current and voltage quantities that are used to determine status and metering values. With additional data from generators, power plants and renewable resources and other DER (Distributed Energy Resources), control centers can automatically provide detailed information about the grid. Reliability of the electrical power service therefore can be monitored in real-time.
Modern SAS are smarter with software enabled devices, digital sampling and seamless communication networks. These systems provide useful information for the smart grid applications and components. The information includes measurements for metering, protection and wide control applications. Dependable design and use of these systems shall guarantee reliability, including safety and security. Reliable SAS contributes to the overall smart grid reliability. Hence, the role of modern SAS is crucial for the evolution of the smart grid applications
- IEC TR 61850-1:2013 Communication networks and systems for power utility automation - Part 1: Introduction and overview, IEC Geneva, 2013
- A. Altaher, H. Madi, & A. Khashkusha. Real-Time safety: Analyzing coordination time for networked automation systems. In 2021 IEEE 1st International Maghreb Meeting of the Conference on Sciences and Techniques of Automatic Control and Computer Engineering MI-STA, pp. 393-397. IEEE. 2021.
- A. Altaher, H. Madi, & A. Khomsi. Reliability Investigation of Digital Substation Networks Design Using FMEA Technique. International Conference on Technical Sciences (ICST2019). Vol. 6. 2019.
This article edited by Jose Medina