IEC 61850 - What does Free allocation of the Logical Nodes mean?

Often people ask the question: Where should I allocate a specific function (and the corresponding Logical Node) in the hierarchy of: process, bay, substation, regional control center, central control center? 

In the following you will find some description from the Standard IEC 61850-5, a paper from 2001, a question I received the other day, my own brief answer to that question, and two answers from two good friends: Andrea Bonetti (Megger) and Joachim Lange (Solvay).

IEC 61850-5 (Communication requirements for functions and device models; Ed 2022) describes that the allocation is free to allow different architectures and levels were a function (respective a corresponding LN) can be allocated (means implemented).

Excerpt of Clause 9.2.1 Free allocation of Logical Nodes

"The free (arbitrary) allocation of functions or Logical Nodes respectively is not restricted to the common level structure."

The following excerpt of clause 10.1 Need for a formal system description is one of the crucial clauses in the whole standard series IEC 61850:

"Where the data is coming from (sending Logical Node) and is going to (receiving Logical Node), i.e. the static structure of the communication system, has to be engineered or negotiated during the set-up phase of the system. All functions in the IEDs have to know what data to send when and what data they need from functions in other IEDs to be able to fulfill their functions. To control the free allocation of functions respectively Logical Nodes and to create interoperable systems, a strong formal device and system description for communication engineering shall be provided. Such a description (System Configuration description Language) is defined in Part 6 of this standard (IEC 61850-6). This formal description shall also support the data exchange between different tools if applicable."

Be aware that the Logical Nodes are to be understood as a wrapper around a function. In most cases the function as such is behind the facade of the Logical Node. One exception is the Logical Node class FSCH (Schedule). The definition of FSCH contains a well defined state machine that is part of the function of a scheduler.

An old paper from the year 2001 may help you to understand the approach of IEC 61850

The Impact of the coming Standard IEC61850 on the Life-cycle of Open Communication Systems in Substations

By Lars Andersson, Klaus-Peter Brand, Wolfgang Wimmer; ABB Power Automation Ltd., Switzerland

Excerpt from the paper:

1. Free allocation of functions [KHS: and therefore free allocation of Logical Nodes]
2. Extension rules to support new functionality
3. Separation of communication from application issues in a well defined manner
4. Description of the station from the application communication point of view.

Click HERE for the paper published in the year 2001.

Question:

Hi Karlheinz,
I’m a system engineer with a question on IEC 61850 in substation automation.
In a ring with all IEDs and two RTUs, are the RTUs only SCADA gateways, or can they also host SAS control logic (e.g., with a T500’s basic logic capability)?
Should a SAS operate autonomously from SCADA or higher-level PLCs, and if so, should the IEC 61850 RTUs implement control logic for outage restoration, load shedding, etc., to ensure autonomy?

Answer from Karlheinz Schwarz

Dear xx,
Thanks for contacting me.
IEC 61850 is independent from centralized or decentralized approach. It depends on the philosophy of the utility how to architect the system. Functions could be in the multi-functional IED (Relay), bay controller, substation controller, SCADA, control center, ...
IEC 61850 may be used to run schedules in control IED right behind the electrical connecting point of a home, factory, ... using the LN FSCH - Scheduling.
In Germany we have the so-called FNN Steuerbox that uses schedules for limiting the power usage ...
Hope that helps.

Answer from Andrea Bonetti

IEC 61850 does not prescribe where control logic must be located (read it as the famous sentence "free allocation of the Logical Nodes").
The decision is up to the system designer and the utility’s operational requirements. If autonomy of the HV ring is desired, logic may be placed in RTUs, bay controllers, or other IEDs so that the system operates without SCADA. Any such requirement would come from utility or regulatory specifications, not from the IEC 61850 standard.

There is no IEC 61850 requirement that mandates where control logic must be located — whether in RTUs, IEDs, or higher-level systems.
IEC 61850 specifies how devices exchange information and how to engineer all of that (SCL engineering), not where the logic resides.
Whether the HV ring is autonomous is purely a system design choice defined by the utility’s operational philosophy, national regulations, or internal standards — not by IEC 61850 itself.
If autonomy is required (e.g., for outage restoration or load shedding without SCADA), the designer can choose to implement logic in RTUs, bay controllers, or other IEDs so they can function without higher-level supervision.
Obviously it depends also on the voltage level. Usually, higher voltage level –> less integration. Lower voltage level à more integration.
But there are exceptions to this rule like always.

Answer from Joachim Lange

In case of classical terminals, neither the terminal number nor the terminal function is defined in any standard. Personally, in case of CFC implication I use UDx baycontrol blocks, defining „my signals“ and a group with the  "GOOSE exchange" signals
- in case of blocking signals like in double busbar structures I do this as well, because I use busbar selective reverse blocking in dependance of position information,
- this means that disconnector positions enables/disables the blocking transmission to its circuit breaker protection.
It is even useful to avoid that a send out blocking signals triggers during test a not involved feeder.
Some grid companies use f.e. blocking signal in combination with breaker failure. This means when signal is not reset in time they trigger the breaker failure protection.
So the CFC function is really case wise.
We have in our house in the UD1 group all signals which are used for bay supervision.
Philosophy: I decentralise load shedding and automation functions into the bay control level ( discrete frequency / voltage levels with hysteresis).
Such bay controller measures autonomously its conditions.
I provide from above (Scada) the enabling/ disabling signals or mode selections ( power level ) or setpoint correction signals.
The advantage is that a single device failure may not impact a hole system.

Note that Andrea Bonetti (Megger), Joachim Lange (Solvay), Dr. Ghada Elbez (KIT), and I will conduct a comprehensive training starting 09.-13. March 2026 Karlsruhe (Germany) and 21.-25. September 2026 Karlsruhe (Germany).
We will provide the details in the next weeks. Stay tuned.

Here are the logos for that training:

How To Bring Plant Engineers To The Table When Cyber Issues Are Discussed?

In my career as electrical and IT engineer I have experienced that engineers are quite often not invited to discuss the measures and plans for critical infrastructure protection with IT personnel.

It is completely different compared to the world of electric power system protection - I mean the applications of protection relays. Protection engineers are (in my understanding) the most crucial engineers. They are very important for the reliable delivery of electric power. Protection engineers are likely to attend any meeting when it comes to the reliability of the power flows. Protection engineers know what to do ... software people may help to implement the "what" and the IT personnel may help to solve the communication issues ... but the crucial parts are dominated by protection engineers!

Mr. Vytautas Butrimas, a globally well known engineer involved in cyber security of control systems has briefly discussed the "Berlin wall" between IT personnel and plant engineers.  

Click HERE for the four page paper written by Mr. Butrimas.

Either of the groups involved believes that his or her group is the center of universe. There is little communication between the IT personnel and the engineers. 

There are so many semipermeable walls between, e.g., politicians, company lawyers, economists, IT experts, and plant engineers. There is usually no way that experts from any layer are allowed to talk to the experts from the other layers. In the end: Each layer feels independent of the other layers ... which leads to what we see these days ... and may be even more in the future. Have you heard of a discussion between a power protection engineer and a lawyer or even a medical doctor?

It would help medical doctors to understand the basics of electric power system reliability ... and so on. Because medical doctors (and all other people of a society) depend 100% on available power.

So in the end: (Electrical) Engineers should be honored by the society ... the problem may be that the engineers are not wearing white coats but wear safety boots, safety helmets, goggles,  protective gloves, ... a single doctor may harm a few people ... a protection engineer may harm millions of people during a blackout caused by a misconfiguration of protection equipment.

IEEE PES published Report on "Centralized Substation Protection and Control"

The IEEE Power System Relaying Committee has published a very comprehensive report worth to be read by power system engineers dealing with substation protection and automation (partlywith focus on the  North American market):

Centralized Substation Protection and Control IEEE PES
Power System Relaying Committee Report of Working Group K15
of the Substation Protection Subcommittee
(2015-12)

Excerpt of the Introduction:
"The power grid is now more dynamic than ever before and newer tools are increasingly developed to manage the grid better. Renewable energy sources are changing power system characteristics at a time when utilities are also focusing on improving customer service and resiliency of the grid, by using advanced monitoring and control technologies....
In addition, communication technologies are advancing and related international standards are maturing to be deployed in substation environment. ... the IEEE Power System Relaying Committee has formed a working group to prepare a report describing and analyzing the state-of-the-art technologies for centralized protection and control (CPC) within a substation...
This report starts by reviewing the advancements in substation protection and control technology. Next the report describes CPC and reviews its history. Then the report reviews some of the existing
technologies that can support CPC.
Finally the report concludes that CPC technology, when appropriately applied, significantly improves the reliability of protection and control systems and the power grid at an affordable cost - with enhanced applications capability and maintainability for both hardware replacement an software upgrade."

Click HERE for the full report [pdf, 80 pages, 4.4 MB]

The report gives inside views of the challenges in managing future power systems. Power systems are very complex - and will become more complex in the near future. In addition to the fact that "utilities are also focusing on improving customer service and resiliency of the grid" the utilities are quite often focusing on increasing their shareholder values ... and outsourcing many tasks. In the German "vdi nachrichten" (a very famous weekly German technical newspaper) I read yesterday an interesting statement of the new president of the BDEW (Bundesverbandes der Energie- und Wasserwirtschaft):

Translated: " ... Unfortunately the industry invests too little in view of the challenges in research and development. The German Pharmaceutical industry employs 40,000 humans in R&D laboratories.
In the energy industry there are not such research and development mechanisms. That is not because of the fact that our industry is come to a hold and does not see challenges. It is financially no more able to implement comparable research activities. We have no more enterprises, which can do that. Everyone knows nevertheless around the difficult situation of many large energy enterprises. Also normal public distribution utilities cannot advance innovative developments in the storage area."

Original: " ... Leider investiert die Branche angesichts der Herausforderungen zu wenig in Forschung und Entwicklung. Die deutsche Pharmaindustrie beschäftigt 40 000 Menschen in F- und E-Laboren.
In der Energiewirtschaft gibt es solche Forschungs- und Entwicklungseinrichtungen nicht. Das liegt nicht daran, dass unsere Branche verstockt ist und Herausforderungen nicht sieht. Sie ist finanziell nicht mehr zu vergleichbaren Forschungsleistungen in der Lage. Wir haben keine Unternehmen mehr, die das können. Jeder weiß doch um die schwierige Lage vieler großer Energieunternehmen. Auch normale Stadtwerke können bahnbrechende Entwicklungen im Speicherbereich nicht voranzutreiben."

Vendors, too, are struggling with similar challenges. We need more universities to compensate these situations. When it comes to the definition and application of information exchange systems in power or energy systems, we could be quite happy that we have the well accepted standards IEC 61968/70 (CIM), IEC 60870-5-104, DNP3, IEC 61850, IEC 61400-25, ICCP/TASE.2 (IEC 60870-6), ...

The Aging Workforce in the Electric Power domain

The Electric Power Utility domain is looking for many electrical power engineers all over. One example can be found by searching the simplyhired.com:

Click HERE for a search on power system engineer

The search results in 38,329 hits for the U.S. allone !!
Some 6.000 hits are related to protection, 800 to SCADA, and 55 to IEC 61850, 12 to DNP3.

Click HERE for a search on electrical engineer

The search results in 86,596 hits for the U.S.
72 are related to IEC 61850 and 20 to DNP3.

Power systems require skilled and experienced engineers. How to become an experiences and skilled engineer? By education, training, learning-by-doing, …

During the year 2011 a lot more electric power engineers and IT experts have received one or the other education and training with regard to IEC 61850.

I see a lot more of interest on the radar screen for 2012.

Have you ever thought about to get a training that build up your skills in the application of IEC 61850 and related standards? Note that in many of the open positions you can read something like: experience in relevant protocols and interfaces (IEC 61850, IEC 60870-x, DNP, etc.).

Many people still expect that IEC 61850 is a protocol. It is definitely much more than a protocol.

Click HERE to see some differences.