240V to 480V Equipment Feed

D

dvcraven052256

Member
Location
St. Louis, missouri
Occupation
Electrical Engineer
I am starting new post on a previous question.

In essence I need to feed a couple of motors rated 480V but I only have 240V available. I am have going back and forth with a buck-boost or using a normal 240V/3 to 480V/3 rated transformer listed for back-fed applications. My concern is the motors are controlled via a VFD and I understand the VFD my not like reverse fed xfmr.

My one line (attached) shows a step-up xfmr. reverse fed. I just don't know if this is the correct approach.

Thank you
Dan Craven
 

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  • 240-480V Equipemnt.pdf
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H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
dvcraven052256 said:
I am starting new post on a previous question.

In essence I need to feed a couple of motors rated 480V but I only have 240V available. I am have going back and forth with a buck-boost or using a normal 240V/3 to 480V/3 rated transformer listed for back-fed applications. My concern is the motors are controlled via a VFD and I understand the VFD my not like reverse fed xfmr.

My one line (attached) shows a step-up xfmr. reverse fed. I just don't know if this is the correct approach.

Thank you
Dan Craven
Click to expand...
As like Augie said, use a transformer that is designed for a wye connection. Backfeeding wye/Delta is the problem. The output is on the delta side,so it needs to be corner grounded, or a fault detector. The voltage to ground can be as high as 480. That’s what the vfd doesn’t like. With a delta/wye step up transformer, XO is bonded, so voltage to ground would be 277.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
dvcraven052256 said:
I am starting new post on a previous question.

In essence I need to feed a couple of motors rated 480V but I only have 240V available.
Click to expand...
Are the motors the only 480V load? Have you considered if the motors can be converted to 240V? when i have done it it was just a matter of changing a few connections.
 
tortuga

tortuga

Code Historian
Location
Oregon
Occupation
Electrical Design
Birken Vogt said:
It is a VFD system so he would also have to change the VFDs and who knows what else.
Click to expand...
I recently dealt with a platen press that was 480V and needed to run on 240V it was by far more economical to change the VFD as it had small motors like the one the OP is posting, I even changed the heat tubes to 240V, it still was cheaper than a 480V transformer & gear, but I had help from the manufacturer of the press.
 
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