1631   change in CDC for MMXU.Hz

Created: 02 May 2018

Status: Discussion (red)

Part: Part 7-4 (2010; Edition 2)

Links:

Page: 58

Clause: 5.10.12

Paragraph: DO: Hz

Category: Issue for edition 3 of this part

Issue

This Data Object is defined as having a <<MV>> CDC in -7-3 which has a Mandatory Data Attribute of <<mag>>
However frequency can be measured of individual phase voltages and should therefore really have a CDC of <<WYE>>

Proposal

Change Hz CDC to WYE

Discussion Created Status
Agree. The knowledge in which phase th frequency is measured could be important. To add this as a requirement at least for next edition. 09 Nov 18 Discussion (red)
... to add
the alternative to handle backwards compatibiliuty is to create a new DO something like <<phHz>> or such, to distinguish which type of value is being made available 		03 May 18 Discussion (red)
Frequency could be measured in an IED on all phase inputs .. in fact I saw this in an IED with Modbus mappings which prompted this TISSUE
So it is not a issue of whether the system frequency is effectively consistent across all phases because of the rotational speed of the generator ... although inverter fed systems that may not be true either. Hence knowing which phase the frequency or being able to get the frequency of each phase individually is important and hence it is necessary to change .Hz to use WYE CDC 		03 May 18 Discussion (red)
I think if we model an instance of a MMXU, we refer to a three phase system where the phases are energized e.g. by a three-phase generator. Here the frequency is normally equal in the phases, isn't it?
But right, you could calculate individual phases.
Nowadays also inverter can feed-in energy in only one phase. I don't know if they will be able to influence the frequency in one phase so much.I think there will be instantiated in each measuring point one MMXU.
But also in the draft of 61850-7-420 in the extension of MMXU the Hz is of CDC MV. So I don't see a need to change the CDC (we get backwards compatibility problems). 		03 May 18 Discussion (red)

 

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