Step up transformer

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packersbay

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So i need to wire a air compressor for customer, he currently has a 240v service 3phase. The compressor is 480v 15hp 125 psi. I was looking into a step up transformer 240v to 480v. Wanted to see if you guys any suggestions on this situation and what kind of transformer will be best.
 
packersbay said:
So i need to wire a air compressor for customer, he currently has a 240v service 3phase. The compressor is 480v 15hp 125 psi. I was looking into a step up transformer 240v to 480v. Wanted to see if you guys any suggestions on this situation and what kind of transformer will be best.
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240 delta to 277/480 wye would be the best. Probably 30KVA.

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An electric motor is a rotating transformer, and many if not most 480V motors can be reconnected to operate at 240V, in the fashion of reconnecting a dual voltage transformer primary.

So the reconnection is the first thing to investigate.

If you can't reconnect the system, then the delta:wye transformer suggested by electrofelon looks like a good choice.

Jon
 
The motor is usually the easy part, the starter may be too small, and the control voltage may not adjustable. Still cheaper to change the starter than install a transformer. The next issue is wire size, if it is a long run, put the transformer at the panel if you go that route. Less voltage drop, smaller wire size would be needed.
 
My first choice would be to check and see if the motor can be reconfigured to run on 240V, my second choice would be to buy a new motor that will run on 240V. All you have to do to change the motor is match the frame and horsepower. Even if you have to buy a new starter I can't imagine it would be more expensive to change the motor than it would be to set a transformer, set a disconnect for the secondary, run a grounding electrode conductor for the secondary, and do all the wiring necessary for a transformer.
 
ActionDave said:
My first choice would be to check and see if the motor can be reconfigured to run on 240V, my second choice would be to buy a new motor that will run on 240V. All you have to do to change the motor is match the frame and horsepower. Even if you have to buy a new starter I can't imagine it would be more expensive to change the motor than it would be to set a transformer, set a disconnect for the secondary, run a grounding electrode conductor for the secondary, and do all the wiring necessary for a transformer.
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I agree. Plus there will ongoing losses through a transformer that the customer will have to pay for.
 
synchro said:
I agree. Plus there will ongoing losses through a transformer that the customer will have to pay for.
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Absolutely. That’s something people often don’t think about. Even if it’s only 2% losses through that transformer, that’s like having a 200W heat lamp running 24/7/365 in terms of not just the direct energy cost, but also the added heat into your building to where if the space is air conditioned, adds to the cost of running the A/C.

A new, energy efficient 460V motor would ultimately cost less all around (again, assuming the existing motor is not dual voltage).
 
If this is just a garden variety compressor with a standard NEMA motor and NEMA starter it seems to me to be a no brainer to just reconnect the motor for 240 volt. As a bonus, I think that 15 HP just happens to fall where you would need the same size starter for 480 or 240. Just change the OLs and the coil.
Now if this compressor is something more exotic like a screw type with a control panel and other stuff commonly found on a screw type package the maybe things could be different.
 
texie said:
If this is just a garden variety compressor with a standard NEMA motor and NEMA starter it seems to me to be a no brainer to just reconnect the motor for 240 volt. As a bonus, I think that 15 HP just happens to fall where you would need the same size starter for 480 or 240. Just change the OLs and the coil.
Now if this compressor is something more exotic like a screw type with a control panel and other stuff commonly found on a screw type package the maybe things could be different.
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Don’t forget, the starter to motor wiring also needs upsizing.

Many newer screw compressors are variable speed. The VFD would likely have to be replaced.
 
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