480V, 3PH, UPS with 4 hours backup battery

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wsbeih

Member
Location
USA
I need to design a high reliability power back up for 4x 20HP motors (480v, 3PH) each for a critical application.

ATS with GEN is not an option. The client requested to design a UPS that can supply these motors and that can endure 4 hours during a power outage.

Anyone came across such an application? I have attached the the one-line for the system. But I need help with specifying such a UPS with backup batteries for this application.

Thank you for your input in advance.
 

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JFletcher

Senior Member
Location
Williamsburg, VA
I found a UPS that can supply 60 kilowatts for 18 minutes... $72,000... you would need 13 of those. I didn't check the voltage or if they were three phase, but if that is in the ballpark, you're looking at roughly a million dollars.
 
publicgood

publicgood

Senior Member
Location
WI, USA
Design has several challenges. First, in-rush of motors. You’ll want to size based on starting of 6X. Is one starting or all. If all, you could be at a 500kVA UPS. Next, 4 hrs battery. In both VRLA and LIB, you be looking at 8-30 cabinets for that type of runtime - no worth it. Buy a generator.
 
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swaneesr

Member
Location
Centerville
480V, 3PH, UPS with 4 hours backup battery

When faced with a similar situation in both the US and Asia, we installed a backup generator and ATS. I am not sure why this is not an option for your application. I have done this four times with success, two each US and Singapore.

Also for my application, a UPS on the control voltage is provided to keep the control system alive. This gives the process operators time to shut down the process in an orderly fashion if normal power is not restored. Critical systems get UPS power. Three types of control power. UPS backed, non-UPS, and Utility power.

4 hours is a long time to be on battery backup at that required draw. Laws of physics are hard to ignore. I am just wondering if the design criteria can be modified/reconsidered.







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Jraef

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
You can use VFDs set up for DC input and feed them from the battery system, then have a charging system floating the battery bank continuously. The VFDs will eliminate any inrush current issues. If all 4 motors run continuously at the same time, you could use one VFD sized for the aggreagate currents.

You would need a battery bank and charger to support 80HP for 4 hours at roughly 660VDC (the minimum DC bus voltage needed to support 460V output), which will not be cheap, but it will likely be cheaper than a bunch of pointless double conversion UPS systems capable of handling the inrush.
 
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swaneesr

Member
Location
Centerville
480V, 3PH, UPS with 4 hours backup battery

Jraef said:
You can use VFDs set up for DC input and feed them from the battery system, then have a charging system floating the battery bank continuously. The VFDs will eliminate any inrush current issues. If all 4 motors run continuously at the same time, you could use one VFD sized for the aggreagate currents.

You would need a battery bank and charger to support 80HP for 4 hours at roughly 660VDC (the minimum DC bus voltage needed to support 460V output), which will not be cheap, but it will likely be cheaper than a bunch of pointless double conversion UPS systems capable of handling the inrush.
Click to expand...

You are of course correct that a drive installation off a common DC bus can be installed. We commonly do this in web line applications where some of the motors are generating and shedding power back onto the bus. It also works well in fan applications since you can shed power back to the bus, this allows you to be more aggressive in control tuning. Slowing down more quickly can be done if you can shed power to the bus instead of dissipating over a braking resistor.

In the end, it will require a large amount of energy storage to meet the OPs customer requirement and that is going to cost money.

4x20HP @ 4 hours. Those are tough numbers to deal with.




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cpickett

Senior Member
Location
Western Maryland
Occupation
Electrical Engineer
Bare minimum numbers:

4 * 20HP = 60kW
4 hrs runtime * 60kW = 240kWh

From internet searches 12V deep cycle batteries are around 100Ah capacity

12V * 100Ah = 1.2kWh

Would need 200 12V batteries bare minimum. Realistically probably double that for conversion losses and to cover battery capacity decrease over the life of the batteries. So 400 batteries plus racking, wiring, fusing etc certainly won't be cheap but depending on what it's backing up might not be out of the question. Of course maintenance costs will not be cheap either.
 
Besoeker

Besoeker

Senior Member
Location
UK
cpickett said:
Bare minimum numbers:

4 * 20HP = 60kW
4 hrs runtime * 60kW = 240kWh

From internet searches 12V deep cycle batteries are around 100Ah capacity

12V * 100Ah = 1.2kWh

Would need 200 12V batteries bare minimum. Realistically probably double that for conversion losses and to cover battery capacity decrease over the life of the batteries. So 400 batteries plus racking, wiring, fusing etc certainly won't be cheap but depending on what it's backing up might not be out of the question. Of course maintenance costs will not be cheap either.
Click to expand...
And weighing close to 7 tonnes. And costing maybe about $25k
 
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swaneesr

Member
Location
Centerville
Based on my past projects, I could see this being a $300k custom system not including installation, shipping, engineering, drawing package etc.

Total seems like $400k to $450k for a quick swag number.





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Jraef

Jraef

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Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I wonder how Tesla Power Wall batteries would stack up to this application? I’ve not yet been involved in pricing them, but the concept is the same. I have a customer right now who has a solar farm backed up by them, he wants to run a 250HP drive and pump motor from it, I’m only involved in the drive part of it. It might be rude to ask him what the Tesla batteries cost him, but he also may not actually know because it was a packaged installed system with the solar panels, trackers, inverters and grid tie system. Rude of not, I’m going to ask him when I get a chance.
 
Besoeker

Besoeker

Senior Member
Location
UK
publicgood said:
Understood.

Note: Due to the volume of electrolyte, by code, each battery cabinet would require thermal runaway management. That cost alone is about $10k, per cabinet.
Click to expand...
Our systems were on open frame battery racks in an air conditioned switch room. Yes, that is also a cost factor.
 
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wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Jraef said:
I wonder how Tesla Power Wall batteries would stack up to this application?
Click to expand...
Powerwall is $5,900 for 5 kW AC power and 13.5 kWh AC capacity. Currently in short supply.

Tesla Powerpack might fit the bill. Specs are 50 kW AC power and 210 kWh AC capacity per unit. I'm unclear on cost, per wikipedia it was $400/kWh 1.5 years ago.

Cheers, Wayne
 
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Ingenieur

Senior Member
Location
Earth
each motor draws ~23 A
you spec 2 items: inverter and batteries
you need ~100 A x 4 hr ~ 400 A hr, use 500
you need 1.35 x 480 or 650 vdc
using a 24 v cell ~ 28 in series at 100 ahr each
so 5 sets in parallel, 140 each 24 v 100 ahr batteries

80 kw/100 kva inverter
this is a common industrial ups
inrush should be minimal during transition
you can start the motors is sequence

https://eaton-upssystems.com/?gclid=EAIaIQobChMIz9XSnbLW2wIVCzppCh194wz-EAAYASAAEgJlvfD_BwE
 
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rlundsrud

Senior Member
Location
chicago, il, USA
Why not recommend to the customer a combination of both a genset and a UPS. The UPS would only be there for the transition from utility to generator power so it would not have to be sized for more than a couple of minutes of runtime but you would probably want to specify something in the 15-minute range. You could certainly use a UPS with less than a minute of capacity but I would think you would want it sized to handle a complete system shutdown in the event that the generator failed for some reason.

With this design the UPS handles the transition while the genset spools up and then once the genset is online the ATS would transition from the UPS to the genset. Make sure you include in your calculations whatever controls equipment is required to operate these motors. This could involve one or more computer systems, a control cabinet, Etc.
 
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