×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to size a UPS for 60 hp, 480 3 ph motor?

How to size a UPS for 60 hp, 480 3 ph motor?

How to size a UPS for 60 hp, 480 3 ph motor?

(OP)
Been asked to determine a budget cost to provide a UPS feed motor as listed above.  Never sized a unit of this size before so not sure where to start.  Any suggestions / thoughts would be nice.

RE: How to size a UPS for 60 hp, 480 3 ph motor?

If the motor is the only load, you will have to ensure that the UPS can handle the starting inrush current. Most static UPS will have trouble with that. Either they will go to bypass (the will treat this as overcurrent) or simply go down.

You need to get the UPS manufacturer's recommendation. At minimum consider a solit state reduced voltage starter or a VFD, this will help a great deal to keep the UPS size within limits.

RE: How to size a UPS for 60 hp, 480 3 ph motor?

(OP)
Should have stated that already have a VFD on the motor.  This UPS is needed to keep the motor running during loss of utility power till the back-up generator is on-line.  Since the generator should be on-line in a couple of minutes, the UPS would be sized for to keep the motor running for 5 minutes at full load.

RE: How to size a UPS for 60 hp, 480 3 ph motor?

60 hp is roughly 60 kVA.  So it probably needs to be at least that big.  On a VFD, something on the order of 100 kVA should work.  But that's a big UPS.  If you really only need to bridge the gap until the generator start, you might be able to work into the overload range of the UPS and get by with something smaller.  

I'd talk it over with two or three UPS vendors.  And write your spec to explain **precisely** what the UPS is required to do.  Try to shift as much of the risk to the supplier as possible.  If you just order a UPS and it doesn't work, it will be your problem.  If you write a performance spec, the UPS supplier will be responsible for making it work.  

RE: How to size a UPS for 60 hp, 480 3 ph motor?

For this one motor by itself why not build a battery bank to directly feed the VFD DC buss. Just figure out the amount of kWH draw or Ah  required and put together a battery bank with the necessary capacity. You can fuse and diode isolate it from the buss so it just takes over from the AC if the AC drops below a certain voltage.

You also need to backup any controls so the motor doesn't get stopped by the start input when the power goes out.

RE: How to size a UPS for 60 hp, 480 3 ph motor?

VFD manufacturers often include some power outage ride-thru features in standard drives. Some drives will decelerate when power is lost and continue to operate on energy recovered by decelerating the load inertia. When the power returns, many drives can restart automatically regardless of the coasting speed of the motor.

Some manufacturers may be able to supply a battery back-up system as described by LionelHutz above.

Third part accessory suppliers may also be able to supply a battery back-up system. One is http://www.bonitron.com/. There may be others.

RE: How to size a UPS for 60 hp, 480 3 ph motor?

I think Hutz's suggestion is by far the cheapest! I would go for that myself and a small standard UPS for any required controls.

If it's a VFD you could possibly set back the motor's speed 10% or so to extend the battery run.

100A @ 600V
(100)6V batteries deep cycles.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: How to size a UPS for 60 hp, 480 3 ph motor?

Is this the only load in facilitty that require UPS power?

RE: How to size a UPS for 60 hp, 480 3 ph motor?

(OP)
This is not the only UPS load but would be our first motor to be operated under / after a UPS.
All great suggestions - just wish it would be a standard option from a drive manufacture.  

RE: How to size a UPS for 60 hp, 480 3 ph motor?

"Standard options" means engineering and associated documentation costs, so to VFD manufacturers they consist of things that get requested over and over where it makes sense to engineer them once and offer them to the customer base. In my 25+ years of working with VFDs, this is exactly the second time I have heard someone ask for this. That's not to say it can't be done, I'm just explaining why it will never likely be a "standard option".

I once came up with engineering on a list of options available for a VFD manufacturer using a lot of the custom projects I had worked on prior to coming to work for them. They offered them and nobody bought a single one, mostly because their version needed to be slightly different than mine anyway, which made it an engineered special anyway.

http:/www.jraef.com
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

RE: How to size a UPS for 60 hp, 480 3 ph motor?

If this is to be connected to an existing UPS is already large enough to take care of other loads, and this motor is not a big part of the total UPS capacity, a motor with VFD should not be a problem.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources