IEC 61850 is a standard for the design of electrical substation automation and is a part of the International Electrotechnical Commission's (IEC) Technical Committee 57 (TC57) architecture for electric power systems. The IEC 61850 standard is an innovative approach to substation automation that will result in improvements in both performance and costs in protection systems and data acquisition.
The standard defines:
- The communications interfaces
- Provides a set of common object models for substation plant and functions
- Methodology of managing substation automation and field devices
- A million acronyms
Abstract data models defined are mapped to MMS (Manufacturing Message Specification) and GOOSE (Generic Object Oriented Substation Event). LANs using high speed switched Ethernet is used to run these protocols over TCP/IP networks while attaining response times below four milliseconds for protection systems. Complete storage of the configured data for the system is defined by The Substation Configuration Language (SCL).
|Introduction & Overview
|Glossary of Terms
|System & Project Management
|Communication Requirements for Functions & Device Models
|Configuration Description Language for Communication in Electrical Substations Related to IEDs
|Basic Communication Structure for Substation & Feeder Equipment
|- Principles & Models
|- Abstract Communication Service Interface(ACSI)
|- Common Data Classes (CDC)
|- Compatible logical node classes & data classes
|Specific Communication Service Mapping (SCSM)
|- Mappings to MMS(ISO/IEC 9506 – Part 1 & Part 2) & to ISO/IEC 8802-3
|Specific Communication Service Mapping (SCSM)
|- Sampled Values over Serial Unidirectional Multidrop Point-to-Point Link
|- Sampled Values over ISO/IEC 8802-3
Table. 1 Structure of the IEC 61850 Standard
Standardised data representation as Logical Nodes are used to model primary process object, protection and control functionality in the substation. The model begins with a physical device that connects to the network. A physical device (LPHD) contains one or more logical devices (LLN0). Multiple devices can connect to a single physical device to act as a gateway providing standard representation of a data concentrator. A logical device contains one or more logical nodes. A logical node is a power system function logically related to a grouping of data and associated services. The definition of Logical Nodes and common data classes related to substation application is found in Part 7.4 and 7.3 of the standard. Structure of an IEC 61850 object name: (Logical Device) / (Logical Node) $ (Functional Constraint) $ (Data) $ (Attribute). e.g. Relay1/XCBR1$ST$Loc$stVal.
The abstract data object and services are mapped onto the MMS, defined in Part 8.1. MMS is an international standard messaging system used between networked devices and/or computing applications for transferring real time process data and supervisory control information. Devices provide reporting to the higher level systems such as HMIs and Gateways.
GOOSE is grouped data sets that are transmitted within a time period of four milliseconds. This is done using a controlled model mechanism for protection relays that are based on Ethernet connection over a Local Area Network (LAN). To ensure precise transmission speed and reliability mechanisms such as GOOSE directly embedded into Ethernet data packets and works on publisher-subscriber, virtual LAN with priority tagging and enhanced retransmission mechanisms. GOOSE messaging is designed to be vendor independent.
Part 6 of the IEC 61850 standard, Configuration Description Language for Communication in Electrical Substations Related to IEDs allow the formal description of the dialect between the system automation system and the switchyard. The SCL file is based on a set of schema files defining XML tags and rules defining an object model that describes the substation structure, the IEDs, the network and the data type objects used to configure an IEC 61850 system. Data representation for substation device entities, associated functions represented as logical nodes, communication systems and capabilities can be included. A complete representation of data as SCL is to have comprehensive interoperability amongst different devices of a substation.
SCL File Extensions:
Substation Configuration Description (SCD) file: The file contains substation, communication, IED and Data type template sections describing complete substation detail. The .ssd file and different .icd files contribute in creating a .scd file.
Substation Specification Description (SSD) file: Complete specification of a substation automation system including single line diagram for the substation and its functionalities (logical nodes). The file contains substation part, Data type templates and logical node type definitions and does not require the IED section.
IED Capability Description (ICD) file: To complete the system configuration the .icd file needs to be supplied by each manufacturer. This file defines the complete capability of an IED device. The file contains a single IED section, an optional substation part which symbolises the physical entities conforming to the IED and an optional communication section.
Configured IED Description (CID) file: The .cid file can be considered as a stripped down .scd file with the communication section for a specific IED. This is the file used in the IED configuration tool to configure an IED.
Instantiated IED Description (IID) file: This .iid file is used to transfer data in a project for a specific IED from the IED configurator to the system integrator tool. The .iid file contains an IED section, the IED's communication parameters and the IED's data type templates. It can also contain a substation section with the binding of functions (logical nodes) to the single line diagram.
System Exchange Description (SED) file: The .sed file is for the exchange of data between different configurator tools of different projects and contains a subset of data from the .scd file with additional IED and SCL information.
I have been a SCADA Para Professional for over 10 years in the industry with extensive experienced in all aspects of large distributed SCADA systems. I have recently been involved in re-engineering an IEC 61850 Station Bus Substation Automation System with multi-vendor IED’s using a "Top-down Engineering approach" to "System Specification" and "Integration". Although the engineering of the signals and setting up of templates and functions for IEC 61850 is extremely complex, it simplifies system specification and integration for building a complete system. IEC 61850 cannot be approached in the same way as other legacy systems. The disadvantage of IEC 61850 for an electrical substation automation standard is the complexity of the initial research and development before implementing a complete system.
Major advantages are the descriptive strings used naming every element, standardised object names are defined to relate to the data. The object name is the object's address allowing multi-vendor interoperability, essentially plug and play. Improvements are found in both costs and performance from the perspective of equipment, integration, expansion, failed in service and commissioning when taking into account whole-life costs.
The IEC 61850 standard has been defined in collaboration with manufacturers and users to create a uniform, future-proof basis for the protection, communication and control of substations.