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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.

IEC 61850 integration with the power plant automation, control and protection system
IEC 61850 integration with the power plant automation, control and protection system (photo credit: Ertugrul Saglam via Linkedin)

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.

Interoperability does not mean interchangeability, but it is a prerequisite for it. Interchangeability without impacting the system behaviour would require devices of identical functionality. This would imply the standardization of functions, which is outside the scope of IEC 61850, as it would hinder further development of functions for substation automation.

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.

IEC 61850 modelling of hardware and functions
Figure 1 – IEC 61850 modelling of hardware and functions

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.

However, all these IED-tools have to be compliant with IEC 61850. This means that the reading, handling, and writing of configuration files has to be according to the Substation Configuration description Language (SCL) of IEC 61850 as regards the standardized data model, the data access (services) and all communication connections.

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.

Substation Configuration description Language (SCL) describing all aspects of the electrical system
Figure 2 – Substation Configuration description Language (SCL) describing all aspects of the electrical system

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 communication procedures are described by the seven-layer ISO/OSI model, called stack. The selected stack is MMS (Manufacturing Message Specification) over TCP/IP and Ethernet as used in mainstream communication technology. It is the use of mainstream means that allows benefiting from the fast advancing communication technology.

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.

IEC 61850 communication model
Figure 3 – IEC 61850 communication model

Station control and monitoring are the basic tasks of a substation automation system. This comprises:

  1. Local operation of the switchgear and other medium-/ high-voltage equipment
  2. Acquisition of switchgear information and power system measurements
  3. 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.

Figure 4 represents a configuration replacing serial protocols by IEC 61850 for vertical communication; that is, for the communication between electronic devices and the control system.

The communication between electronic devices (horizontal communication) remains hardwired.

Integrated system based on IEC 61850 vertical communication
Figure 4 – Integrated system based on IEC 61850 vertical communication

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.

Integrated system based on IEC 61850 vertical and horizontal communication
Figure 5 – Integrated system based on IEC 61850 vertical and horizontal communication


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.

IEC 61850 does not define the content of an algorithm to protect a generator, motor or transformer, but the very deep implementation of the IEC 61850 model into the device architecture brings the best benefits to the user. This is not only in respect to communication, but also when it comes to data consistency throughout the whole power plant.

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.

ABB IED REG670 generator protection relay
Figure 6 – ABB IED REG670 generator protection relay

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 example, the REG 670 already incorporates the IEC 61850 definitions in the user documentation as the following example of a pre-configured package shows. Such a configuration is intended to be used for hydro-, gas- and pump-storage applications.

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).

REG 670 predefined package for hydro-, gas- and pump-storage applications
Figure 7 – REG 670 predefined package for hydro-, gas- and pump-storage applications

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.

ABB's 800xA System
Figure 8 – ABB’s 800xA System, the industry’s most intuitive system interface, provides a consistent method for accessing enterprise-wide data and for interacting with multiple applications from any connected workstation in the plant or office.

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.

RET 670 and REG 670 integration to ABB's System 800xA
Figure 9 – RET 670 and REG 670 integration to ABB’s System 800xA

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

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Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

6 Comments


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