Reuse Transformer

[Zinsky]

I have a project where there is an existing 150kVA 480/277 to 208/120 transformer that is feeding a dimmer directly. We are removing it, so the transformer is no longer in use.

But I need to add a new 225A 208/120 panel to service the area. I was originally planning to add a new smaller transformer, but I was wondering if anything was stopping me from reusing the transformer they already have.

Safety-wise I think its fine, but I'm second guessing myself about other hidden negative effects. Efficiency losses or something else that might bleed them in the long run. Is there a down side to this plan?

 

[winnie]

Take a look at this old thread. You would need to know the core loss and load loss ratings of the existing (oversized) transformer, the same ratings for the new transformer you would consider installing, and the actual expected load (not the maximum that the panel can supply, but the actual load profile).
http://forums.mikeholt.com/showthread.php?t=138581

In general, the larger transformer will have larger 'core' losses, meaning that it will burn more energy just sitting there...but will have lower 'load losses' meaning that less will be wasted on operation.

The larger transformer will have lower impedance. It might have the same impedance rating, but the rating is relative to the output current rating of the transformer. This means higher potential short circuit current, but also has the benefit of better load voltage regulation.

So: negative effects to consider: possible higher no-load losses (balanced by the possibility of greater efficiency in operation), possible shorter service life (if the existing transformer is showing signs of aging or abuse), possible need to use higher AIC rated components (not likely at this power levels, but worth checking).

Most likely: it will save money to use the existing equipment.

-Jon

 

[templdl]

I have a project where there is an existing 150kVA 480/277 to 208/120 transformer that is feeding a dimmer directly. We are removing it, so the transformer is no longer in use.

But I need to add a new 225A 208/120 panel to service the area. I was originally planning to add a new smaller transformer, but I was wondering if anything was stopping me from reusing the transformer they already have.

Safety-wise I think its fine, but I'm second guessing myself about other hidden negative effects. Efficiency losses or something else that might bleed them in the long run. Is there a down side to this plan?

What raises a red big flag to me is that you even have a 150kva Y-Y 480/277-208/120 transformer. Is this what the nameplate shows?

 

[Jraef]

What raises a red big flag to me is that you even have a 150kva Y-Y 480/277-208/120 transformer. Is this what the nameplate shows?

Excellent point.

But Zinsky, just because you have a 480Y277V SYSTEM, doesn't mean the step-down transformer is that way. It's more likely to be a 480-208Y120V transformer where the 480V side is connected in Delta. Where that 480V comes from is irrelevant.

 

[Zinsky]

Fair points. Im sure Jraef is right with your assumption, but I'll dig out the faceplate pictures and read a bit more into it before making a decision. Thanks for the assistance.