Power measurement composition in SCL

To have an insight into how P and Q measurements are composed exactly (from what U measurement and from what I measurement), so that we have a full understanding what the P and Q measurements exactly mean (switch state) so that we make our decisions on loading and overloading the grid on trustful data instead of assumptions

Link power measurement data to its input current/voltage measurement

Whether this is possible depends on how you structure your data model - and if the vendors support it. The most common situation is having three-phase measurements in the logical node MMXU. This has several data object for power measurement, such as

Both the underlying common data classes WYE and MV do not have any attributes that hold a reference to the input values.

There is no way in the function itself.

HOWEVER, MMXU also allows you to add in the data objects A and PPV|PhV . So if you have the current, voltage and power measurement per phase, you have already a connection by convention. This is not something I have seen very often, though in vendor IED I would say is would be uncommon.

You can make this link by putting current/voltage and power measurement in one logical node MMXU

Link power measurement to topological measurement inputs

The basic idea here would be to have the logical nodes be referenced in topological structure, and this would allow modeling the composition.

This route, as well, depends on the design of the data model, or which logical node do you use to map the measurement in IED - MMXU or MMXN. The “problem“ is the limitation in SCL is that the element LNode must be unique within the substation section. !So it can be linked once and only once!

This limitation makes is a bit hard for the logical node MMXU exclusively.

Possible, but requires MMXN logical nodes to be used in combination with MMXU logical nodes.

Link through communication mappings

Another ways to model the composition of inputs to a power measurement would be through the ExtRef element. This one is used to describe digital input of a SampledValue, GOOSE and Report information. The nice thing is that this input element can be allocated at any logical node in the receiving IED. You then could think of a scenario where a logical node MMXU with the data object as above representing power measurement also holds ExtRef(s) element pointing to the sampled value streams received from the process.

This mapping can only be done in a digital substation setup where measurement is connected through sampled value streams to the bay device doing the measurement.