In the current MMXN logical node,
the Current (Amp) and Voltage (Vol) is defined as a MV (no angle).
This is correct for most measurement mode where the angle is
meaningless since a reference for this angle doesn't exist.
The issue is when we want to model a single phase Synchrophasor
(C37.118). In a 3-Phase system (MMXU), we simply set the reference of
the angle (angRef) to "Synchrophasor", in MMXN we cannot do so since
the DO type is defined as a MV.
Proposal
Change the DO type of the Current (Amp) and Voltage (Vol) in MMXN to
CMV to allow using the logical node for synchrophasors.
Discussion
Created
Status
I would like to clarify that MMXU IS used as the data source for synchrophasors publication as per IEC61850-90-5. So is is just a logical extension that MMXN would be the single phase version of it.
Regarding the RSYN use case, I agree that nobody has expressed this functionality this way in the IEC61850-7-500 TR, but there is no reason why you would not be able to use it that way. In this TR, the received TCTR/TVTR will in fact be converted to a synchrophasor locally and then used for the RSYN. Having them already available just simplify the process. Anyway this is another discussion.
Instead of discussing this use case, I would prefer to give another use case, which is the distribution application. In distribution application, many applications are single phase based, and the synchrophasor application is no exception. Some PMUs already allow single phase application while some are specifically targeting this use case: https://tcipg.org/sites/default/files/papers/2014_Q1_SDQ2.pdf
Hope that this use case is clearer.
01 May 17
Not Applicable
In the use case about RSYN has got a mistake: It isn't true that RSYN uses the synchrophasor values of MMXU. The sources of values are the LN TVTR. (see part TR 61850-7-500)
MMXU and MMXN shall be used mainly for operational purposes, not for synchrocheck/synchronizing.
25 Apr 17
Not Applicable
To answer Bruce question, the synchrophasor angle is time referenced. (AngRef = Synchrophasor, 4.2 from IEEE C37.118)
In short, it is referenced to a virtual nominal frequency cosine synchronised with the UTC time base. This allow comparing a signal angle with any other synchrophasor values elsewhere on the grid.
A simple single phase application of synchrophasor is a RSYN LN which use synchrophasor referenced MMXN values to compute synchronisation between 2 signal.
In this application, the RSYN LN only need to receive and analyse the synchrophasor referenced angle of MMXN node from each side to figure out if the phase of those 2 signals is synchronised.
Hope this simple use case clarify the need.
29 Mar 17
Not Applicable
No change is needed. The problem statement is unclear. What is the "angle" for a single-phase measurement? Maybe it is "absolute angle" but it could also be "angle volt-amp". The first case is covered by MMXU because you need to know the specific phase for absolute angle. The second case is covered by MMXN.PwrFact.
24 Mar 17
Not Applicable
I agree that MMXU could be used for this purpose, but the MMXN LN is specified as the LN to used for single-phase application.
One of the reason for this is that we doesn't always know or care which phase we monitor.
A second reason is that, even if we know the phase, and use MMXU, we would need 6 version of LN objects to represent it correctly: (WYE with PhsA, PhsB, PhsC, DEL with phsAB, phsBC and phsCA). Then if we want matching harmonics and metering LNs this become an implementation nightmare.
Non-phase-related version (single phase) LNs (MMXN,MHAN,MMTN) address single-phase application perfectly.
The only issue is that synchrophasor referenced angles where probably never considered when defining the MMXN logical node, That is perfectly understandable. But I think that a solution using MMXN is the best and the cleanest solution to address this application.
23 Mar 17
Not Applicable
For this purpose you can also use MMXU.
At first, the WYE CDC allows to contain one, two or three phases - if this is demanded by a specific application. At second, even if all three phases are available in the MMXU, you can choose which one you want to transfer to a client application. Naturally, if you make single phase comparisons, you need to transfer the same phase from everywhere.
23 Mar 17
Not Applicable
MMXN is mainly used in application where a single phase reading is used. So a typical use case of this is simply in any synchrophasors application using a single phase. Many devices publishing synchrophasors allow to use a single phase input and compute frequency and synchrophasor on this input. This function logically map to MMXN in IEC61850.
Another solution could be to add 2 additional DO named cAmp and cVol of type CMV.
Since the complex values are only required for synchrophasors application, this solution would avoid any eventual interop issues.
22 Mar 17
Not Applicable
In the next revision of part 7-4 the voltage and amps of MMXN are described as "Non-phase-related AC rms current/voltage". See IEC document 57_1645e_INF_61850-7-4-v21.
So the right CDC will be MV. CDC of Amp and Vol cannot be changed.
The use case for LN MMXN and synchrophasors is not clear.