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Delta - Wye Transformer Ohm Resistance Testing X1 X2 X3

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L

LaROcque

Member
Location
Phoenix AZ
Occupation
electrician
Hello,
New to the forums here and want to reach out for help.
Under a lot of pressure to get a job done, and second guessing myself.
Brand new Delta Wye transformer install.
480v Primary to 120/208 secondary.

Before I energize everything, I am testing and metering everything as there is no room for errors on this... like there ever is.
This will determine if we get future contracts, and ...anyway. Today is a Saturday, and this must be operational Monday.

Question....
when I test H1 H2 H3 to ground, I get infinite.
when I test X1 X2 X3 I get resistance.
There is no neutral on the primary, but neutral is required on the secondary Wye.
I am stressing and trying to remember if this should read any resistance to ground or if should be infinite.
Test lead to X1, other lead to ground, and get resistance.
Same for X2 and X3.

Is this normal or do I have bad windings.
Any help to refresh my memory. I am really stressing on this one and second guessing myself.
 
G

g-and-h_electric

Senior Member
Location
northern illinois
Occupation
supervising electrician
As I recall, XO is grounded, and there is no "H0". Therefore the secondary windings should show resistance to ground, and the primary should not. Sounds like you are good to go.

I know the feeling of being on a "mission critical" job, and doubting ones self..... Deep breath, take your time, and double check the schematic on the transformer ........

Hope this helped.


Howard
 
M

MD Automation

Senior Member
Location
Maryland
Occupation
Engineer
On your Wye secondary there should be an X0 terminal (the mid-point of the Wye). This is where the neutral is derived from. This XO is likely bonded to ground via a wire or strap. So any reading from a secondary winding will show a low resistance connection to ground thru that bond.

See the pic below for that ground connection on the Wye midpoint. Hopefully this helps visualize the connection from any X1, X2 or X3 to ground.

1615650933815.png
 
Last edited:
L

LaROcque

Member
Location
Phoenix AZ
Occupation
electrician
Oh man...thank you both very much.
Yes there is an X0 for sure; I should have mentioned it...sorry about that.
This is a tremendous help to ease my scrambled brain.
Thank you again.
 
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