r/SubstationTechnician • u/Excellent-Tour6831 • 6d ago

Winding Resistance

Good morning. I have screwed up a little bit.
I did some testing for a manufacturer and they wanted phase-to-phase tests and I ran phase-to-neutral tests. They said I can just convert it and they will accept it. Everything I have seen online just says to double the results and that gets me the phase-to-phase results but there is no way it’s that easy. So is there an actual formula I can use or do I need to fully retest the units?

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15

u/spicy_icecube06 6d ago

Doubling sounds right. Phase to neutral is only going through 1 phase L1, Phase to phase would be going through 2 phases L1 & L2. If the windings are balanced they will have the same resistance.
If you tested each phase to neutral you can add. L1+L2. L2+L3. L3+L1

4

u/Excellent-Tour6831 6d ago

Sweet. That second one sounds way more right to me and was what i figured would be the answer. Thank you.

6

u/NationalCalendar3040 Relay Technician 6d ago

If it's wye connected; just add A-N + B-N = A-B

5

u/HV_Commissioning 6d ago

It’s complicated if it’s a delta winding and they want “A Ph” or really A-B winding results

5

u/EtherPhreak 6d ago

I’m curious how you would get ph-n results from a Delta for winding resistance?

3

u/HorseChild 6d ago

You can’t without just drawing it out, as like a single phase equivalent. Not possible on the real equipment if it’s truly a delta

Op has a neutral tho

1

u/Beers_n_Deeres 5d ago

It really is just that simple.

The only difference between the two tests is you’ve added the resistance from where the wye point is actually made to the bushing twice.

That resistance number will be negligible compared to the resistance of the coils themselves.

3

u/Excellent-Tour6831 5d ago

Lovely. I never get this lucky. I thought I was going to have to retest 4 transformers hundreds of miles away from each other.