Mateus

[Mateus]

On a 3 phase 208 ac system how does one leg become 105v to ground and other legs 117 to ground, and how can it be adjusted?

 

[mgookin]

Welcome to the forums!

If that's what you're getting at your service from the electric utility, I'd call them. Sounds like one of their transformers is a bit ill.

If you're getting these readings somewhere else, I'd follow it back to the source (service point) and find out where it gets out of balance.

 

[kwired]

On a 3 phase 208 ac system how does one leg become 105v to ground and other legs 117 to ground, and how can it be adjusted?

More information is needed, lets start with some of the simplest things first.

Is it loaded fairly evenly?

Do you have these or similar voltages with no load?

Is this a service voltage or a separately derived system that you have control of the transformer?

What happens with load changes?

If this is service you probably need to have POCO investigate their equipment, if your load is not causing the problem.

If this is customer owned transformer - you do need to go through some of what I previously mentioned on the primary side to make sure the supply isn't the issue, but otherwise you may have winding troubles - maybe a short from turn to turn, or maybe if it has adjustable primary "taps" they are not all connected to same level.

 

[ggunn]

On a 3 phase 208 ac system how does one leg become 105v to ground and other legs 117 to ground, and how can it be adjusted?

Do you have a solid neutral connection?

 

[templdl]

On a 3 phase 208 ac system how does one leg become 105v to ground and other legs 117 to ground, and how can it be adjusted?

Let's start here. Do you have 208v from A-B, B-C, and A-C?

 

[gar]

131213-1358 EST

Mateus:

You have very severely distorted waveforms, or your line to line voltages can not all be 208 and produce the line to neutral voltages you measured. The vectors do not correlate.

You said ground. Make sure the measurements are line to neutral, and measure all the line to line voltages as was mentioned above.

.

 

[don_resqcapt19]

If there are line to neutral loads on the system, the first thing I would be looking for would be a neutral problem, but as others have said additional voltage measurements would be helpful.
line to line
line to neutral
line to ground
neutral to ground

 

[petersonra]

On a 3 phase 208 ac system how does one leg become 105v to ground and other legs 117 to ground, and how can it be adjusted?

L-G voltages include the voltage drop on the N.

Check the L-N voltages.

 

[templdl]

What happened to Mateus? We asked a lot of questions and it seems as if he disappeared.

 

[petersonra]

That happens a lot with first time posters.

 

[JimmyElectro]

good stuff

good stuff

Thank you Senior Members, got some smart people out there, keep it up!

 

[gar]

131213-2042 EST

If all the phase angles are about 120 degrees apart, and the voltages are sine waves, then it is not possible to get the voltage readings presented in the first post. Since line-to-line voltages were not measured we have to use the assumed values of 208 V. Draw the vector diagrams.

.

 

[templdl]

That happens a lot with first time posters.

Yes, it's obvious and results is us spinning in circles when there is no interaction with the OP. Again, shooting at shadows.