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.