Smart substations that are capable of responding to real-time events form a critical component of smart grids. Automation technology adds intelligence to the substation by incorporating communication devices with controls and analytics. While communication is managed by routers, protocol converters and gateways, intelligent electronic devices (IEDs) are used to control, analyse and monitor process parameters, as well as provide system protection. Communication networks comprise lower-level data links, as well as physical layer and multiple application layer protocols. The addition of automation devices makes the substation architecture and technology landscape highly complex. As a result, standards and protocols are developed to help define the architecture of substation automation communication systems.
Communication protocols determine the manner in which information flows between devices including control stations and IEDs. There are over 50 communication protocols available for legacy substation automation systems. Various legacy communication protocols including Modbus, Ethernet internet protocol (IP), DNP3 and IEC 60870-5-104 have been used at the utility level for substation automation systems. However, these protocols have several limitations as many of them are vendor specified, have serial interface, low bandwidth, limited network devices and can be implemented only till the bay level and station level. The architecture has limited capability to fit corporate communication technology and expand networks. Utilities also face the issue of interoperability between IEDs supplied by different vendors during the expansion of an existing electric substation.
As a result, substation vendors are moving away from a serial-based to Ethernet-based IEC 61850 client/server communication standard. This standard supports interoperability between devices, applications and functions through standardised data models and information exchange, and can be applied at the process level. In the case of IEC 61850, the application model and communication stack remain independent, implying that applications can be modified without changing the communication stack.
IEC 61850 standard
The IEC 61850 standard is a reference architecture for electric power systems, which simplifies the substation automation procedure, optimises device selection, increases efficiency and allows flexible configuration of communication networks. It is a part of the International Electrotechnical Commission’s (IEC) Technical Committee 57, set up during the mid-1990s. The final component of the 10-part IEC 61850 was declared as an international standard in 2005.
Under IEC 61850, the primary process objects as well as protection and control functionalities at the substation are modelled into different standard logical nodes, which can be grouped under different logical devices. There are logical nodes for data/functions related to the logical and physical device. Further, there are various schemes for reporting data from the server through a server-client relationship, which could be activated based on predefined trigger conditions. Generic substation events are defined for quick transfer of data for a peer-to-peer communication mode. This is further subdivided into generic object-oriented substation event (GOOSE) and generic substation status event (GSSE).
IEC 61850 defines setting group control blocks, thereby enabling the user to switch to any active group as per the requirement. Schemes are also defined to handle the transfer of sampled values using sample value control blocks. IEC 61850 supports various command types, which include “direct” and “select before operate” commands with normal and enhanced securities. In addition, the standard defines the substation configuration language (SCL) for storage of configured data of the substation in a specific format.
The standard defines abstract data models, which can be mapped to a number of protocols, including manufacturing message specification, GOOSE, sampled measured values (SMVs) and web services. These protocols can run over transmission control protocol (TCP)/IP networks or the local area network using high speed switched Ethernet for protective relaying.
In the case of lower-layer protocols, IEC 61850-based communication is typically implemented over TCP/IP and Ethernet networks. However, for some IEC 61850 functions, user datagram protocol might be used. The process bus function and GOOSE run directly over Ethernet.
IEC 61850 also lists the environmental requirements for substation conditions. These pertain to supply voltage, electromagnetic interference, temperature, humidity, barometric pressure, pollution, and corrosion. These standards are required as communication devices have to be protected from harsh environmental conditions such as electric and magnetic fields and energy power surges created by substation equipment.
IEC 61850 provides an object-oriented solution designed to support the implementation and maintenance of substation automation applications. It is a comprehensive standard for all communication functions and provides substantially more features and benefits as compared to the traditional supervisory control and data acquisition (SCADA) protocol.
The standard provides for a non-proprietary technology with supports devices from multiple vendors. It also provides interoperability between devices, applications and functions through standardised data models and information exchange. It further provides the flexible configuration of communication networks, which simplifies the automation architecture, optimises device selection for certain applications and increases efficiency.
A unique feature of IEC 61850 as compared to other standards is that it defines how data is represented but does not define what function or data is available in any particular type of IED. Suppliers can implement any functional feature by providing a description in the SCL file.
Further, IEC 61850 supports high speed peer-to-peer messaging using the GOOSE and GSSE definitions designed to support system protection applications. It also supports a process bus that minimises substation wiring requirements by converting status and analog inputs to digital information.
Significantly, the standard can be used over many different protocols. The object-oriented data representation in the form of standard naming conventions, structures and formats provided by IEC 61850 makes it easier for third-party applications to access information from IEDs sourced from multiple vendors. The abstract communication service interface (ACSI) as defined by the standard is independent of the communication protocols, making it possible for applications and databases to remain unchanged despite changes in the protocols. These measures reduce the effort of application design engineers as well as allows auto-configuration of some portions of interfaces and applications.
Substation automation is becoming increasingly important as the complexity of the grid increases with growing generation and demand, and with the increased peniteration of intermittent renewable energy sources in order to coordinate, control and protect the infrastructure. Recent developments in communication standards and protocols for substation automation present significant opportunities for utilities to improve their operations.
IEC 61850 provides multiple benefits associated with the abstract model, independent protocol, standardised object names, self-describing devices, a wide range of high-level services and SCL. These features allow inter-device operability and implementation of new capabilities; eliminate procurement ambiguity; and lower costs associated with installation, commissioning, migration, integration and extension.
IEC 61850 is designed to future-proof networks in order to meet the evolving needs of utilities as it allows applications to be modified and extended without changing the communication stack. It also allows devices from different manufacturers to be combined into the network infrastructure, building long-term network flexibility and expansion.
Given the multiple advantages, utilities across the world have already started implementing IEC 61850. While its implementation gains momentum, other technologies and standards continue to evolve. For instance, the DNP3 protocol has evolved to incorporate self-description capability of IEC 61850. In addition, initiatives are being taken to extend IEC 61850 automation functionalities to areas beyond substations, such as in wind energy generators, hydropower plants and distributed energy resources. Meanwhile, regardless of the standards, it is extremely important for utilities to understand the quality and interoperability of the technology devices.