Running 50HP 480V Motor from UPS

[rockman7892]

I have a customer that is looking for a solution for running a critical 50HP 480V motor (currently fed from MCC) for a duration of 2-3hrs in the event they loose utility power. Has anyone ever done something similar using a UPS & VFD combination (I don't think motor and UPS direct connected would cooperate together) or some other similar solution?

I've heard of this solution being used for short time temporary durations (in seconds) to bridge gap until backup gen power comes online but never have seen anything for this long of a duration? It seems like adding a backup gen for this one 50Hp motor would be overkill.

 

[waross]

UPS plus Diesel Generator.
Let the UPS carry the motor until the generator has time to run up and sync, or an orderly shutdown if the generator fails to start.
Darlington Nuclear Plant does this to keep their 10,000 HP feedwater pumps for the main steam generators on-line. I'm not sure about the shutdown procedure.

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

 

[dpc]

50 kVA (roughly) for 3 hours requires a big battery. Also, it's unlikely a UPS sized for the running load could start the motor across the line. You don't mention the starting method.

If they cannot afford any motor downtime, then Bill's suggestion should work. A standby generator makes a lot more sense if they can tolerate the brief outage.

 

[itsmoked]

Back of the napkin figuring:
$4k 50HP VFD
$49k LiFePO4 batteries.
$5k Charger
$10k Bits&Pieces
$10k Engineering
---------------------
$78k
Call it $100k
and that gets you 3 hours.

What can you get for that in generator - good for 48 hours?
If you're willing to go with a used generator?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

I think Keith may be a little generous. I once did a project for the Air Force involving keeping a 25HP air conditioning compressor running on batteries for 90 minutes. It took a 75 kVA UPS with a battery system that was huge (back in the day of lead-acid batteries) and a soft starter for the motor. That was in around 1995 and it was almost $75k back then for half the HP and half the time.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

Well that was what I'd sort of charge for it and that was for 50% more battery than the numbers demanded.

If you called up a UPS company I have no doubt they'd mark that up 2x.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[FreddyNurk]

In theory it'd be possible to hook up batteries via a VFD's DC bus, and use that as the standby capacity. It'd need a decent amount of OEM support, and some means of charging the batteries if whatever the device used isn't up to the task. I know there are at least a couple of VFD manufacturers that run active front ends and allow for a shared DC bus. I'd expect most of them would baulk at the prospect though.

In practice? I'd probably go with a larger UPS (are flywheel units still a thing?) and a diesel generator, and allow for enough time to start the generator and transfer over.

EDMS Australia

 

[itsmoked]

There are spinning-mass back-up diesel generators. They're called Rotary Diesel UPSes.

They use inertia to prevent power interruption AND to start the engine. They're pretty perplexing mechanical gizmosis. I was asked how to keep a field of CNC machines from seeing hiccups which are devastating to the CNC processes. I had a long talk with the national supplier of these RUPSes and he said, "The smallest unit starts at just about exactly one million dollars...

An example

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

I worked on one of those rotary UPS systems for supplying continuous power to the switchgear control systems of the Celilo Converter Station of the Pacific Intertie near the Bonneville Dam on the Columbia River. It was an 800HP AC induction motor connected to a flywheel and a DC generator. Besides just being the temporary source of DC during transfer to the diesel generator, it was designed to provide breaker operating power for up to 2 hours as a backup to the diesel generator, ie if station power was out for longer than their fuel supply lasted, they were assuming they could find and truck in more fuel from Portland in that 2 hours. The consequences of that converter station going off line for any length of time were very very dire. I don’t know what that entire system was worth because I only worked on the AC controller side, but it was definitely a 7 figure project.

Most engineering problems can be solved by being drawn out on the back of a big enough check...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[itsmoked]

Texas Instruments had a fab in my little edge of Silicon Valley town. Unfortunately the corner of town it was in has lots of short power interruptions. Interruptions on the order of a minute that occur ehhh once every two weeks or so. A power interruption of more than about 100ms is catastrophic to a semiconductor fab as exotic gas supplies trip off, furnaces trip off, robotics controllers have spasms, and it wipes all products in production. Some of these products have weeks long fab times. After a few of these losses TI brought in 8 diesel rotary UPSes. They were all built into semi trailers which they backed up to the facility on two sides. There were wrist-sized power cords snaking all over the place. I believe they actually kept the engines spinning and essentially opened the fuel valves on power loss.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

The big rotary UPS's by of the type made by Eurodiesel and Piller are impressive machines. One design uses two concentric rotors, one rotor spinning at double the two-pole synchronous speed which acts as the energy store.

Common in bank datacentres and trading floors, and too expensive for hospitals.