The basics of IEC 61850
IEC 61850 is much more than a protocol. The general scope of the standard is designed to support the communication of all functions being performed in a substation. Its main goal is interoperability and this is the ability for IEDs from one or different manufacturers to exchange information and use the information for their own functions.
Providing data transfer is normally a one-way procedure with data flowing from a simple sender to a highly sophisticated receiver, which interprets complex data. This is very often a human being that can read and understand the data with the help of a comprehensive background.
An example is the master-slave communication commonly used in the past, like the information interface of protection devices according to IEC 60870-5-103.
Interoperability as provided by IEC 61850 is much more than simple data transfer, but provides for information exchange between two or more devices of similar intelligence.
The receiver has to understand not only the structure of the data (syntax), but also its meaning; i.e., the semantics based on the data attributes received in a communication.
The standard separates the functionality represented by the data model and the related communication services from the communication implementation (stack).
This makes the standard future-oriented, taking into consideration that the development in communications technology is moving quicker than the development of the functionality in the field of substation automation including protection.
The data model of the standard is an object-oriented one, grouping the data into the smallest possible sets referring to the smallest possible functions to be implemented independently.
These smallest possible data groups or functions are named Logical Nodes (LN). The Logical Nodes and all data and attributes contained are named according to a standardized semantic, which is mandatory. The data model uses terminology familiar to any power system engineer.
In addition, this part contains a device model, which describes the function allocation as well as the properties of each physical device. Clear rules facilitate extensions in applications.
The integration of third party equipment is facilitated and the use of a common language (SCL) avoids ambiguities. Each IEC 61850-compliant IED may be configured using its dedicated tool.
This allows a system integrator to use understandable data from all devices (independently of the supplier) to build a complete system and to assure data consistency.
The information according to SCL may be stored together with the system documentation and re-used in any maintenance situation as well as in case of evolving tools or changing responsibilities for system maintenance, if the system is compliant with IEC 61850.
Engineering data stored as SCL files can be reused, e.g., in case of extensions (additional bays) or refurbishment.
The performance and safety requirements dedicated to substation automation are considered.
The data model and the communication stack are linked by means of standardized mapping, which is the only item to be adapted in case changes in communication technology are implemented. This has no impact on the functions and databases in the system.
Station control and monitoring are the basic tasks of a substation automation system. This comprises:
- Local operation of the switchgear and other medium-/ high-voltage equipment
- Acquisition of switchgear information and power system measurements
- Handling of events and alarms.
This application is related to human operation of the station. The data communication for this application is directed vertically; i.e., from station control level down to bay level (commands of any kind from the operators place) or reverse (binary indications like breakers or isolators position, measured values from instrument transformers and other sensors, events, alarms).
This vertical communication (bay – station) is based on a client-server concept using reporting, command and file transfer services.
Impact of IEC 61850 on the control system structure
Introducing IEC 61850 for integration of electrical systems leads to simplified system structures. The Ethernet based IEC 61850 station bus replaces hardwired and serial cabling for process communication. Besides the process communication, Ethernet allows time synchronization, file transfer and engineering tool access on one physical cable.
Figure 4 and Figure 5 show two possible steps for introducing IEC 61850.
The communication between electronic devices (horizontal communication) remains hardwired.
IEC 61850 is designed to support horizontal communication. In that case, hardwiring between electronic devices (e.g., for interlocking) and communication between electronic devices and the process automation controllers (e.g., turbine control) as shown in Figure 5 are Ethernet-based as well.
Example – Generator protection using ABB’s REG670
Modern generator and generator transformer protection systems based on IEC 61850 offer simplification, connectivity and harmonization towards partial or full integration with the power plant automation and control system.
When it comes to native implementation of the IEC 61850 model, ABB has the IED 670, which is a control and protection platform fully designed for IEC 61850.
The REG 670 as part of this platform already has the ingredients to provide perfect support for IEC 61850 engineering, configuration, testing and commissioning services.
On hardware with Ethernet technology, it is ready to provide single, independent or redundant communication links for various purposes. All data from configuration to process and disturbance data will be transferred and presented according to IEC 61850 logical node definitions/attributes.
The ABB PCM 600 IED tool manager supports the user, not only for configuration and engineering purposes but also provides testing and monitoring features.
For larger applications the transformer protection can be moved to a RET 670 as shown in Figure 7 below.
One REG 670 as main 1 and another one as main 2 protection already protects the complete generator block including the generator transformer. It already has an in-built IEC 61850 interface to the plant control system.
All necessary data, like events, alarms, analog information and disturbance data in Comtrade format can be accessed in System 800xA (see Figure 8).
For visualization and monitoring of REG 670 data, all System 800xA display capabilities, such as freely configurable graphics, faceplates, alarm & event lists are available.
Furthermore, data can be stored in the System 800xA history database for later analysis.
Figure 9 shows the integration of the unit protection to System 800xA. The protection systems consist of two autonomous channels. Ethernet-based IEC 61850 links connect the IEDs to the 800xA control network and the System 800xA server.
A routing device separates the System 800xA control network and the IEC 61850 station bus for save operation.
The consistent vertical integration from the IED up to the enterpise-system level allows the implementation of cost efficient maintenance strategies.
Maintenance relevant information generated by the RET 670 / REG 670 self-diagnosis can be automatically transformed to a maintenance message and transferred to the CMMS (maintenance management system).
Digital substation system integration (VIDEO)
Hardware is only as useful as the software used to manage it. ABB’s range of software tools offer unparalleled ease of use and utility to make deployment, operation and maintenance of protection systems as simple, and safe, as possible.
Source: Future power plant control – Integrating process & substation automation into one system by ABB