480VAC 3phse supply to a 230VAC Single Phase Motor 2

[elfman]

Hello,

I am not a EE, ME working as a controls engineer learning lots and enjoying it, but I have been stumped. I have a job - still waiting to find out if it supply is WYE or Delta 480 3 phase - don't know if that matters. Another vendor is supplying a 230VAC single phase pump motor that I have to supply power to and control. I just don't know how to hook up the motor to my 3 phase 480... I will have a transformer to supply 120VAC control power. How do I hook up this motor? I have attached the datasheet for the pump - if necessary. Thanks much in advance.

"If your parents didn't have any children, then neither will you." -Benny Hill

 

[dpc]

If you have a transformer to supply your 120 V control power, simply make it a 120/240 V system, size it adequately and use that.

There is no way to directly connect a 230 V motor to a 480 V system.

You could also purchase a dedicated step-down transformer to convert the 480 V to 240 V. Or if it is a wye system with the neutral accessible, you can use a small autotransformer to buck the 277 V single-phase voltage down to 240 V.

Or have the vendor give you a 460 V, three-phase motor.

 

[elfman]

Unfortunately, I believe that, even though I am being required to provide power to it and control it, I don't get to have any say as to what was/is approved. I do know that the pump company's cutsheets only show 230VAC motors.

"If your parents didn't have any children, then neither will you." -Benny Hill

 

[jraef]

That is roughly a 1/2HP motor, so .37kW. I would get a minimum of a 1kVA 480-240V transformer and as mentioned above, if you get one that has a 120/240V secondary it can be your control power source as well. Shouldn't be too hard to find.

But there are other important electrical protection issues to be considered, too much for us to do for you remotely like this. Have you considered getting someone qualified to do this for you? A Control Panel Builder would be able to handle this no problem.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[elfman]

Thanks dpc and jraef.

jraef - you mention electrical protection issues that need to be considered but don't mention the issues. You qualify that with there is too much to do remotely. Can you please at least list the considerations? I cannot learn, what I don't know I need to learn. No explainations, just a list of issues to be considered.

Thanks again.

Another question along this line - if I am sizing the transformer to supply a motor, do I use FLA or Startup/Locked rotor current for what the transformer needs to supply?

And again, Thanks very much...

"If your parents didn't have any children, then neither will you." -Benny Hill

 

[jraef]

You have to address primary and secondary protection of the transformer, conductor ratings, lock-out / tag-out issues, door interlocking for the two different voltages or proper conduit use, etc. etc. It's generally something that someone familiar with your local codes needs to do.

Sizing the transformer for an across-the-line starting is not an exact science in the real world, it involves the overload capabilities of the transformer, acceptable voltage drops, a number of variables. But the safe bet "rule of thumb" is to tripple the kW to get the kVA. You might be able to get by with smaller, but you won't know it won't work until AFTER you buy it and install it.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[elfman]

Thanks jraef. I think I have decided to submit my controls based on the site supplying the 230VAC. Spec doesn't require me to provide power to the pumps, just control them. See if I, with proper application of grease on the back can slide out from under that monkey!! Thanks for all the info though.

"To be or not to be, that is the question" - William Shakespeare via Hamlet

 

[jraef]

I think that's a good approach, otherwise you are accepting responsibility for things beyond your control.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[nifrabar]

Jraef,
Somewhere in this thread you mention this must be a 1/2 hp motor.
What makes you do think so?

If indeed this single phase motor is only 1/2 hp I certainly should solve this by using a transformer. Just a single coil to connect to 480V with a tap at 230V.
But... keep in mind that some authorities (like Bureau Veritas and LROS) don't except such a solution and they require a transformer with seperate prim and sec. windings.
(By the way I refer to marine authorities; on shore that might possibly be different).

HTH
-Bart