480v high leg motor issue

[journeyman0217]

It is a delta-delta transformer and has no center tap according to posted nameplate. there are voltage adjustment taps on the high voltage side. If OP is having low voltage issues the tap being used could possibly come into play. Being reverse fed situation he probably should use one of the mid range taps though.

It is tapped to #4 468v...getting 472v on the meter

 

[ptonsparky]

I dont believe it does. So if no winding is bonded to ground, in theory what should my voltages be to ground on the 480 side?

They could be about anything from 0 to 480.

 

[ptonsparky]

It is tapped to #4 468v...getting 472v on the meter

Close enough. Are all three phase to phase the same?

My issue with the back feeding of a transformer would be with a delta wye, not yours.

 

[journeyman0217]

Close enough. Are all three phase to phase the same?

My issue with the back feeding of a transformer would be with a delta wye, not yours.

yes getting 472 on all three phases

 

[ptonsparky]

What are the primary voltages? L-L and L-G
Primary Amperages? Each line.

Is the motor the only load on that transformer?

 

[jim dungar]

I dont believe it does. So if no winding is bonded to ground, in theory what should my voltages be to ground on the 480 side?

When troubleshooting it is best to make, and provide, all of the possible voltage measurements.
L1-L2
L2-L3
L3-L1
L1-N
L2-N
L3-N
L1-G
L2-G
L3-G
N-G

 

[MD Automation]

I know its not referencing a center tap, but what is the dotted line coming off of H1 and X1 referencing?

As Kwired mentioned above... it's a phasing symbol, which shows the phase shift (if any) between the primary and secondary windings.

In a typical delta to wye it shows the 30 degree shift inherent in that type of transformer.

In your delta to delta, it indicates there is no phase shift.

 

[jim dungar]

Is this transformer designed for reverse feed of step up?
It appears to be step down.

Notice the label only says HV and LV. If reference feed was prohibited it would use terms like primary and secondary. Sorgel always had application notes on backfeeding their transformers.

My guess is the transformer is almost 50 years old.

 

[jim dungar]

In your delta to delta, it indicates there is no phase shift.

Yep.
These same phasing dashes are used with delta-wye connections, although they are commonly misinterpreted to be 'grounding' provisions.

 

[ptonsparky]

Notice the label only says HV and LV. If reference feed was prohibited it would use terms like primary and secondary. Sorgel always had application notes on backfeeding their transformers.

My guess is the transformer is almost 50 years old.

Figured that out, eventually.
I couldn't find it online for a a spec sheet.

 

[winnie]

I'm trying to understand it...wouldn't the secondary induced voltage have the same effect as the primary? Wouldnt my voltage on the 480 side be (L1-G 240, L2-G 416, L3-G240)?

Nope. The voltage to ground relation of the primary does nothing to the secondary. Since you have a secondary that doesn't have a center point tap, your choices are to corner ground the secondary or leave it ungrounded.