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

[charlie10]

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.

 

[rbulsara]

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.

 

[charlie10]

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.

 

[dpc]

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.

 

[LionelHutz]

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.

 

[CJCPE]

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.

 

[itsmoked]

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

 

[rbulsara]

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

 

[charlie10]

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.

 

[jraef]

"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:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[rbulsara]

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.