IEC Just Published IEC TR 61850-7-5 ED1 - Modelling Concepts

IEC TC 57 just Published Draft IEC TR 61850-7-5 ED1 - IEC 61850 Modelling Concepts

(57/2253/DTR - 33 pages) - voting closes 2020-09-11

Excerpt from the introduction:

"The standard IEC 61850 provides a very broad range of data models covering as much as possible all application functions in the range of power utility automation. The modelling both in the domains and between the domains show differences which may impact the interoperability. Therefore, some informative guideline is helpful to reach a common approach in application function modelling. A lot of basic functionality is based on the concept of IEC 61850 and, therefore, the same for all application domains. As result, a basic cross-domain part as Technical Report is useful. Domain specific issues are addressed in the Technical Reports 7-5xx (e.g. IEC TR 61850-7-500 for substation automation)."

IEC 61850 Control Model – What is the function of SelectWithValue?

Somebody asked the other day these good questions:

“I tried to understand what “select with value”  or SelectWithValue (SelVal) means, but without success.

What I did understand is it is used for   Select before operate with enhanced security.

Question: What is the purpose of SelectWithValue ?  What is the difference between normal Select and SelecWithValue?”

… questions that have some hidden answer in IEC 61850-7-2 …

You have to look at the service parameters exchanged with the SelectWithValue service request (which is part of the IEC 61850-7-2 control model) – see figure:

The use of the various parameters is this (excerpt, example):

ctlVal (e.g. OPEN) could be used to check against the interlocking information (Logical Node CILO). If opening is not allowed, the server could already at this stage return saying: opening is not allowed.

The ctlNum could be used to guarantee a sequence … further:

With the T a server could figure out that the SelectWithValue is too old to be processed …

I guess this gives a good understanding of the general objective.

In the case of Select, you don’t have these.

When to use Operate Service and when SetDataValues?

The IEC 61850-7-2 abstract services Operate and SetDataValues are both mapped to MMS Write in IEC 61850-8-1. So, what makes a MMS Write service an Operate or a SetDataValues?

The two services and the mapping are sketched here:

The first mapping is showing the Operate service (as part of the control model):

The Operate service is used in conjunction with the control model (defining state machines, select-before-operate, time-activated control,…). Control service models require a special information model: controllable Common Data Classes, e.g., SPC – Controllable Single Point. The model comprises attributes defined by the CDC and the service parameter ctlVal: these are shown in the MMS Variable as a structure “Oper” with the components: ctlVal, origin, ctlNum, T, Test, Check. These have to written at MMS level. These are always required for Operate even if you need just ctlVal !!

The settable DataObjects require the MMS Write as shown in the following figure:

In IEC 61850-7-3 it is defined exactly which services are to be used for the various attributes in the Common Data Classes. Example for controllable DataObjects:

 
Note that the FC=CO is defined in 8-1 !

Note also that client user interfaces (like the IEDScout) may use different service names than 7-2 or MMS.