Transformer for cooling tower.

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darekelec

Senior Member
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nyc
A friend asked me to help him with a question.
What transformer and ocpd to use for a cooling tower that has technical info :
FLA 137A
MCA 142A
Max ocpd 150A
460V 3ø 60 Hz
Is it 112.5 or 150 kVA Y/D (corner grounded) transformer and 350 A ocpd on primary or 400?
I would go with 150 kVA

Is it common to size choose a transformer and load it 100%

Thank you in advance
 
What motors (HP) are involved ? any drives ??

112.5 appears undersized.
What is your primary voltage.
 
Looks like you're stepping up from 208 to 480, yes?
Is the transformer rated for step-up? Does it have a neutral point on the high side?
Corner grounding always raises my suspicion on things like this (like "why don't they have a neutral?). It also makes it harder to install some VFDs.

I'd go with the 150kva, too. Probably have a longer life and leaves room for expansion.
 
Without knowing the nature of the load I would not speculate on the size. I would not even consider anything other than a 208 delta primary with a 480 Y secondary to avoid a lot of other issues. Also this set up will need both primary and secondary OCP. And a GES.
 
Feeding a transformer from a 208Y connected source does not mean you need a wye-connected primary. Nor does the fact that there are no neutral loads on the secondary mean that you need a delta connected secondary. The best transformer to use would be connected delta primary, wye secondary. You can ground the neutral point of the secondary and not run any neutral cables out to the load. It's better that way for lots of reasons.
 
Primary voltage is 120/208 Y 3ø.
150 kVA seems fine.
I will consider different transformers than Y/D. Good catch. 👍
 
With a 150kva you are looking at a 500 or 600 amp primary breaker.
 
I'm not so sure a150kva is necessary. From a load standpoint, I would expect the actual current to be about 95 amps, or only about 80kva. I would look at transformer efficiency at the current level, particularly since I assume this will be a fairly steady consistent load.
 
electrofelon said:
I'm not so sure a150kva is necessary. From a load standpoint, I would expect the actual current to be about 95 amps, or only about 80kva. I would look at transformer efficiency at the current level, particularly since I assume this will be a fairly steady consistent load.
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It might come down to what transformer he can actually get in a reasonable time frame.
 
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