Making IEC 61850 Fit for the Future

Author:Christoph Brunner, it4power, Switzerland

Interoperability is one of the key goals of IEC 61850. As IEC 61850 is more than just communication, that means interoperability as well has to go beyond communication level. IEC 61850 extended with the substation configuration language and the engineering process described in part 6 the scope of standardization, but in edition 1 of IEC 61850, the focus was on communication interoperability. Only with the experience of the first IEC 61850 projects it was possible to learn what was needed to achieve a level of interoperability at the engineering that improves efficiency.
Based on that experience, and the testing sessions in 2013 and 2015, the experts worked hard to extend the specifications in part 6 to make the efficient engineering in a multi-vendor system - a reality. The result is in the draft Ed 2.1 of IEC 61850-6 which has been circulated as CDV earlier this year.

With IEC 61850 standard making progress and being revised, we will see in the future more systems with a need to combine devices that conform to different versions of the standard. While vendors typically will support their old products many years after they have stopped selling them, there may be situations where a system will need to integrate devices supporting different versions of the standard (“Mixed systems”.) So the standard needs to describe how this shall be done. Thus, it is important to not only look at the aspects of communication, but at the aspects of engineering as well. In a mixed configuration, there may be devices conforming to different versions, but there may be engineering tools exchanging files conformed to different versions of the standard. And the files from the engineering tools describe the data model which may as well be based on different versions.

To smoothly support mixed version configurations, not only backwards compatibility is needed; in some cases forward compatibility is required as well. To support that, part 6 introduced in Ed 2 the concept of must understand/may ignore. This concept basically means, that everything in an SCL file that is unknown to a tool (like a new element that was introduced in a later version of the standard) may be safely ignored by the tool, unless it is flagged as “must understan." Since this feature was not yet available in Edition 1, interoperability between tools of Ed 1 to Ed 2 needs to be treated different than interoperability between Ed 2 and future tools.

Another element to be considered is, that devices and tools built in the future shall not need to know the whole history of IEC 61850. So somebody that develops an IEC 61850 product in 20 years when maybe Ed 4 of the standard is valid, shall not need to build in the product a support of Ed 1, 2 and 3 as well. The Ed 4 products shall be able not only to coexist, but as well to cooperate with all kind of older products inherently. To achieve this, some care needs to be taken while developing the new versions of the standard and when developing products. To support this, in Ed 2.1 we will add an Annex to each part of the standard, that discusses compatibility issues between versions as a guideline both for standard designers, as well as for product developers.
Still - in some cases we may not be able to follow these rules from a standard design perspective, otherwise improvement would never be possible. For these cases the standard will explicitly list them in the Annex. They are a set of exceptions for backwards compatibility with older versions of the standard, which need to be considered in the design of a product according to the latest version. Finally, as an Annex to part 6, there will be detailed descriptions, explaining the SCL based engineering process with mixed version systems and describing the requirements on the engineering tools. And this is done for both Ed1 / Ed 2 systems as well as for Ed 2 / future systems.

When realizing mixed systems, it needs to be understood that newer features can only be used between products supporting that newer version of the standard. Also, compatibility aspects need to be considered in the design. As an example, a GOOSE message that is sent from a new device to both old and new devices shall only include DOs that already existed in the old version. If it needs to exchange newer DOs with newer devices as well, this shall be put in a different GOOSE message. This requires that the devices provide enough flexibility with regard to configurability and support enough control blocks.

Now what about Ed 2 and Ed 2.1? Here, the situation is different. Ed 2.1 from a standard perspective is an amendment. Once approved, Ed 2 will not exist anymore; conformance testing will be done based on Ed 2.1. This is like with Ed 1 and TISSUES. Conformance testing was done based on the latest version of the approved TISSUES. It means, that an upgrade of products has to be possible.
So, once Ed 2.1 is released - what is expected for the major parts during the second half of 2017 - we not only will have significant improvements of engineering interoperability and efficiency; we will also have the framework to be able to build mixed systems in an interoperable way.  


Christoph Brunner is the President of his own independent consulting company it4power LLC based in Switzerland. He has over 25 years of experience with knowledge across several areas within the Utility Industry and of technologies from the Automation Industry. He has worked as a project manager at ABB Switzerland Ltd in the area of Power Technology Products in Zurich / Switzerland where he was responsible for the process close communication architecture of the automation system. He is Convener of WG 10 of the IEC TC57 and is a member of WG 17, 18 and 19 of IEC TC57. He is senior member of IEEE-PES and IEEE-SA. He is an IEEE Fellow and he is active in several working groups of the IEEE-PSRC and a member of the PSRC main committee and the subcommittee H. He is international advisor to the board of the UCA international users group. 

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