Choosing 208 V motor or 480 v motor 2

[jor1492]

Hello all,
My motor requiered a power of 29.5 H.P., the voltage in the facility is 208 V 3phase but I am thinking that a motor like this is better a 480 V supply.
I want to know the advantages or disadvantages of choosing a 208 V motor or a 480V motor for a new service, besides the sizes of the wires. Both motors are 3 phases.
Please give me your advices and thanks in advance.

 

[itsmoked]

For starters (no pun intended) do you HAVE 480V in the facility? If you already do then definitely consider using a 30HP 460V motor as it will divorce the starting surge from your 'house' loads somewhat. The wiring will certainly cost much less and be easier to perform. It may have better starting ability too. Have you seen the price difference between the two voltages? Much different?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jor1492]

Thanks itsmoked by the answer.

The facility is 208 V.
The prices between the two voltajes is the same.

What you think about this?
is better get the 460 V equipment and adjust the facility or get the equipment in 208 V? obviously considering other things like efficiency, economic part, etc.

 

[itsmoked]

That's a hard one. It could be very expensive to have 480V brought in. Likely, at least $5k, then monthly 'availability' charges. 480V brings the whole arc-flash PITA front and center too. Your utility has to hang more hardware which they can take absurdly long times to do.

On the other-hand you're going to be adding another 100 Amps of demand to your 208V system which could trigger a new service entrance... sheesh. Going larger is often nowhere near the utility issue though. If they need a bigger transformer they just swap one in which is nothing like a second service - hassle wise.

I think you need to first do a simple economic study. Get quotes for both system possibilities and if they're fairly close proceed to check the hassle and time factors with your local power company. Toss in the odds of needing another 30hp motor or more power for further 'expansion' or the odds of further expansion resulting in moving the facility elsewhere anyway.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Ignoring the economics for the moment, the reality is it is easier to handle voltage than current.

Muthu

http://www.edison.co.in

 

[jraef]

Keith makes great points, but left something out with regard to the "changing the entire plant" option. Right now if you have 208V, most likely everything in your distribution system is rated for 208V (250V max). So if you go to a 480V service, you have to start over from scratch. Most of the wire is likely 600V rated, but your panel boards, motor controls, almost everything else will need to be changed. Then on top of that, assuming you have office and lighting loads that are 120V, you STILL will need to service those loads, which means buying a new transformer to get from the new 480V service to 120/208V.

So your REAL choices are:
1) stick with a 208V motor because you have 208V. Understand there will be essentially NO savings in energy cost by going with 480V vs 208V, kW = kW.
2) buy a transformer to step up your 208V to 480V just for that one motor.
3) change your service to 480V, then buy a new 208V transformers to feed your existing loads.

Option 2 means you now live with the losses in that transformer in addition to the normal losses in the motor whenever that load is running. #2 will end up costing you more in the long run than #1 and gains you nothing in return.

Option 3 means having to live with new transformer losses for all of your EXISTING 120/208V loads, and still getting nothing in return. That would likely cost you more in the long run that option 2!

Just get the 208V motor and move on with life.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[waross]

I would not consider a 480 Volt motor at 30 HP in a facility that is serviced by 208 Volts.
The cost to install 480 Volts will be exorbitant.
Phone a local contractor for a ballpark price to install the smallest available 480 Volt service.
If starting the 30 HP motor is an issue, use a VFD to start it. Still a lot cheaper.
Even if you go Direct On Line starting, consider purchasing an inverter rated motor. It will keep your options open in the event that you are forced to upgrade to a VFD later.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jor1492]

Thanks all, your comments and advices were so usefull.