Specifying IEC 61850 Systems and/or IEDs

Whilst the trend in specifications in the late 1900's was towards "functional specifications" as abstract requirements rather than specific details, the implementation of an integrated system must deal with a significant level of detail.

It is therefore insufficient to specify a system as this:

or indeed specify IEDs as this:

IEC 61850 requires that all the functionality and detailed information that must be communicated from one function to another is specified. 

The specification therefore must deal with the engineering process requirements and SCL files used as well as the detailed Data Model of Logical Devices, Logical Nodes, Data Objects, Data Attributes and elements.

If you don't ask for it, it may not be provided even through the system and the IEDs are compliant to IEC 61850.

Or as I now say: "You have to right to expect to get what you do not specify"

Some have already noted that there is little consistency of implementation between IED vendors, e.g. products are IEC 61850 compliant.. but they are not uniform..some support 3 clients , some support 4 clients.. some support 2 clients..

Naturally - this is all good and proper implementation of the IED.

That is why you first have to understand what your system needs, THEN as a second step (not the first) buy the IEDs that meet those needs.

If you go down to Bridgestone, buy a wheel, come back and try to put it on your car you may find a problem.
The wheel might have four holes and the car have five studs, or even it might be an F1 racing car with one!!

(click to enlarge)

Or a 8mm bolt is not going to be interoperable with a 10 mm nut

All are perfectly correct in their own right.
But as a system, they have to be selected correctly to achieve operation and performance requirements.

Sounds scary? More work?

Well, remember that even with Current Transformer selection we have to choose a P class CT specification of Current Ratio, VA and Accuracy Limit Factor to suit the application, or perhaps a PL class with Turns Ratio,Excitation Current,  Kneepoint and Winding Resistance - "any CT with a nameplate" will not suffice.

The right tools - like Helinks - can make your life MUCH easier.

So, no, the Standard does not stipulate a minimum, maximum or typical no of clients-server relationships.

Hence you have to read the PICS documents that support the IED compliance.
Compliance simply means that IF they need to support (some like Merging Units in principle don't need any) a client-server relationship, it works according to the Standard.  
The PICS tells you if and how many it does support.

Remember the Standard is about giving you the tools to identify what you need and be able to identify if you are going to get them to achieve interoperability in YOUR application.
If you can get to a full understanding of Part 1 of the Standard (there is a reason to work through the Standard in sequence) you will be well prepared to use the Standard as it is intended (using a hammer as a screwdriver, or vice versa, is not a good experience), and in particular Part 1 Chapter 4, para  4:
" ..... but the purpose of the standard is neither to standardise (nor limit in any way) the functions involved in substation operation nor their allocation within the Power Utility Automation System."

It is not prescriptive, it is an enabler - you still have to do your job as an engineer to decide what you want to achieve and how you will achieve it!

Extra Notes: