Thread: Convert from Phase-to-Phase to Phase-to-Neutral for a 3-Phase 3-Wire unbalanced syst

1. Junior Member
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Apr 2017
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Convert from Phase-to-Phase to Phase-to-Neutral for a 3-Phase 3-Wire unbalanced syst

Hi all,

As the title suggests I am trying to understand what is involved in converting from P-P to P-n values.
More specifically I am trying to understand what the process for doing this is, if I had the raw waveform data from two VTs (assuming middle phase is grounded).
i.e Is there a simple vector math I can perform on each measured sample?
Or maybe a more complex trigonometric(/phasor diagram) based solution to get from P-P to P-n.

Please state assumption made and remember its a 3-phase, 3-wire unbalanced solidly ground system.

I also trying to understand what functions other than power metering (eg protection?) I could perform on the obtained signals/variables.

If you have links, manuals, or books to point me to that would be great.

Thanks
Alex

2. Junior Member
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Correction:

*(assuming middle phase input into meter is grounded).

3. gar
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190208-0950 EST

I believe your question is about measurement of three phase power or energy with two single phase watt or watt-hour meters. Your post title did not seem to imply this, but text and drawing did. No wire needs to be earthed or called ground for this measurement.

.

4. you want a ph-n voltage on a system with no n?
why?

5. Junior Member
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Apr 2017
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Apologies for not replying earlier.
I didn't see any notifications in my inbox.

I am trying to understand the wiring diagram and internal (software) operation of a power meter for three phase, 3-wire systems.
My understanding is that while 3-ph, 3-wire (11kV, solidly ground system) do not have a neutral, the transducers (delta-wye) that step down the voltages are in fact grounded and measuring with respect to ground.
Does this not make the inputs into the power meter (/ADC) phase-to-ground?
My best guess then, is that the power meter will then internally convert the phase-to-ground to phase-to-phase? Which is why I mention the p-n to p-p conversion.

Also trying to understand the difference between Aaron method for measuring power using two power meters as gar mentioned above AND a similar but different method where a wye-wye VT has secondary L2 grounded while having a second set of secondary VTs connected as open delta. For example in power generation like one mentioned here:

Thanks and regards
Alex

6. Originally Posted by Ingenieur
you want a ph-n voltage on a system with no n?
why?
A curious question indeed.

7. Senior Member
Join Date
Nov 2007
Posts
835
Originally Posted by Besoeker
A curious question indeed.
Maybe something went awfully wrong when typing things!

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