45kw generator 480v 3 phase hookup

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delfadelfa

Member
Location
Cincinnati, OH
I'm bidding a job installing a 480v 3 phase 45kw generator for a warehouse UPS battery backup system. The UPS batteries only last 30 minutes so they want a backup for the backup. It will only be feeding one 200amp 208-120volt panel which is fed by a 12.5 kva transformer. The transformer sits on the warehouse floor by the panel and is fed by a 480volt overhead buss which is about 30 feet up. I'm planning on removing the feed to the transformer and installing it on the line side of a 100 amp 3 phase transfer switch. And then refeeding the transformer on the load side of the ATF. Then run about 200 feet of EMT to the generator, one run for the feed and one for the control wires. The generator has an 80 amp 3 phase breaker so I'm wanting to run #1 copper for the feed. I've installed a lot of 8 to 20KW generators for residential homes but never one this big and 3 phase. So my question is, do you see any problem with the way I'm planning on doing this install?
 

ron

Senior Member
Did you size the generator?
Are the loads in the 200A panel pretty low?
The 12.5kVA XFMR has a primary rating of 15A, so does the 200A panel serve other stuff too?
How big is the UPS (kVA)?
Be sure you get a good quality gen with a quality solid state voltage regulator, as the UPS needs to recognize the incoming sin wave as "good" or it will not be able to stay off battery.
 

delfadelfa

Member
Location
Cincinnati, OH
Ron - In our bid we are using 45KW Generac generator but are giving an option for a 48KW which runs at lower RPMs and less natural gas consumption. The loads in the panel are very low. A couple of 3 phase 20 amp garage door openers, 10 - 120 volt warehouse receptacles which are used in the mail room for computers, copies, label makers, shrink wrap machine, no big loads. More than half of the panel is empty but the owner's did mention adding a lighting circuit that will control a row of high bay fluorescent lights in the warehouse. I don't know too much about transformer loads, are you saying that I should add 15 amps for the transformer load when I am sizing the generator? I will have to relocate the UPS circuit from another panel which is about 100 feet away and is on a 90 amp 208V breaker, which will be the largest load I will have to add to the generator panel. Thanks

jeremysterling - Generac does offer a remote annunciator Model 8848-0. I will add that as an option in my bid. Thanks
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I'd like some clarification.

You have a 200A 208/120V panel, however the supply to that panel is a 12.5KVA transformer. That is not a standard transformer size, and would only be capable of supplying 34A. Do you have the correct transformer size?

Next, you describe this transformer as the only load on a 45KVA generator. Why such an oversized generator for the load?

-Jon
 

Cold Fusion

Senior Member
Location
way north
delf -
A couple of things are not clear
... I'm planning on removing the feed to the transformer and installing it on the line side of a 100 amp 3 phase transfer switch. And then refeeding the transformer on the load side of the ATF. ...
So the transformer feeds the UPS and the UPS feeds the panel?

I'm bidding a job installing a 480v 3 phase 45kw generator for a warehouse UPS battery backup system. ... It will only be feeding one 200amp 208-120volt panel which is fed by a 12.5 kva transformer. ...
The existing xfm is 12.5kva. As Jon asked, why a 45kw gen?

delfadelfa said:
...The loads in the panel are very low. A couple of 3 phase 20 amp garage door openers, ...
This one confuses me a bit. The garge door motors are on the panel fed by the 12.5kva xfm? And are being fed by the UPS?

delfadelfa said:
... I will have to relocate the UPS circuit from another panel which is about 100 feet away and is on a 90 amp 208V breaker, which will be the largest load I will have to add to the generator panel. ...
Several things in here:
You mention a "generator panel". Is this a 480V, 3ph panel directly off of the gen?

Where do you get the 90A, 208V to feed the UPS? Are you also installing another xfm between the gen and a 208V panel?

This also sounds like there must be an existing transfer switch between the existing 200A panel and 12.5kva xfm, where the UPS can feed the existing 200A panel?

The 12.5 kva xfm, the gen feeding the xfm and also feeding a 20kw(?) 208V, 3ph UPS, a 45kw gen feeding loads handled by a 12.5kva xfm - are all puzzling.

cf
 
Ron - In our bid we are using 45KW Generac generator but are giving an option for a 48KW which runs at lower RPMs and less natural gas consumption. The loads in the panel are very low. A couple of 3 phase 20 amp garage door openers, 10 - 120 volt warehouse receptacles which are used in the mail room for computers, copies, label makers, shrink wrap machine, no big loads. More than half of the panel is empty but the owner's did mention adding a lighting circuit that will control a row of high bay fluorescent lights in the warehouse. I don't know too much about transformer loads, are you saying that I should add 15 amps for the transformer load when I am sizing the generator? I will have to relocate the UPS circuit from another panel which is about 100 feet away and is on a 90 amp 208V breaker, which will be the largest load I will have to add to the generator panel. Thanks

jeremysterling - Generac does offer a remote annunciator Model 8848-0. I will add that as an option in my bid. Thanks


It seems you went from small loads (of which I was surprised to see on a UPS), to adding the 90A UPS Panel.

You may understand exactly what you are trying to do, but I am confused...Maybe you can clarify this a little. Maybe put a list together and explain it some?????
 

delfadelfa

Member
Location
Cincinnati, OH
This is the existing setup: 480v - 3 phase overhead buss feeds a floor mounted transformer.

(( I may have misread the name plate at 12.5KVA because 12500VA divided by (208x1.732) = 34.69amps. I didn't even think about it because it's a big transformer. It may have been 125000VA but that would be 347amps. It's being fed by 1/0 copper from the 480v overhead buss. It's an old General Electric building and all of this equipment is original so I don't think they under sized it))

The transformer secondary is 2.5 inch greenfield feed with 4/0 copper feeding a 208/120v 200 amp main breaker panel.
Nothing in this existing panel is on the UPS system.
I am not adding a panel only a ATS and generator.
--------------------------------------------------------------------
This is what I'm bidding on:
Cut primary feed to transformer at floor level.
Insert a 480v - 3 phase - 100 amp ATS - Line side from overhead buss - load side feeding transformer.
Add wiring from a 45KW - 480v - 3 phase generator (about 200 feet away) to ATS by the transformer.
Remove UPS 90amp - 208V - single phase - circuit from another panel (about 100 feet away) and run it to the existing panel that will be fed by the generator.
 

catchtwentytwo

Senior Member
Did you size the generator?
Are the loads in the 200A panel pretty low?
The 12.5kVA XFMR has a primary rating of 15A, so does the 200A panel serve other stuff too?
How big is the UPS (kVA)?
Be sure you get a good quality gen with a quality solid state voltage regulator, as the UPS needs to recognize the incoming sin wave as "good" or it will not be able to stay off battery.

Ron is right, it is very important that the UPS and generator interact well, a quality voltage regulator and correct gen sizing are a must. Remember, the UPS will draw more current after being on battery during the recharge cycle.

What does the UPS manufacturer recommend?
 

Cold Fusion

Senior Member
Location
way north
This is the existing setup: 480v - 3 phase overhead buss feeds a floor mounted transformer.

(( I may have misread the name plate at 12.5KVA because 12500VA divided by (208x1.732) = 34.69amps. I didn't even think about it because it's a big transformer. It may have been 125000VA but that would be 347amps. It's being fed by 1/0 copper from the 480v overhead buss. It's an old General Electric building and all of this equipment is original so I don't think they under sized it))

The transformer secondary is 2.5 inch greenfield feed with 4/0 copper feeding a 208/120v 200 amp main breaker panel.
Nothing in this existing panel is on the UPS system.
I am not adding a panel only a ATS and generator.
....
Ahhh - that is a lot less puzzling

cf
 

Cold Fusion

Senior Member
Location
way north
...Remove UPS 90amp - 208V - single phase - circuit from another panel (about 100 feet away) and run it to the existing panel that will be fed by the generator. ...

...The loads in the panel are very low. A couple of 3 phase 20 amp garage door openers, 10 - 120 volt warehouse receptacles which are used in the mail room for computers, copies, label makers, shrink wrap machine, ...

I'd probably want to do a load study. You are adding a significant load - the UPS. The gen is only good for 125A @ 208V.

And, of course there is the issue of the gen being an SDS and needing a 4W transfer switch.

cf
 

delfadelfa

Member
Location
Cincinnati, OH
The generator will be 480v and will be feeding the 3 wire primary on the 480v transformer. So, does this mean if the neutral is not switched in a transfer switch it's not considered a seperately derived system?
 

RUWired

Senior Member
Location
Pa.
Not seeing the whole picture. If the Generator and transfer switch are feeding the transformer directly, the neutral conductor from the gen set is of no use.It would not matter if the neutral is switched or not, because it is not needed. IMO the gen set would be set up as a SDS and only the EGC should be ran to the transfer switch and transformer.

Rick
 

Cold Fusion

Senior Member
Location
way north
Not seeing the whole picture. If the Generator and transfer switch are feeding the transformer directly, the neutral conductor from the gen set is of no use.It would not matter if the neutral is switched or not, because it is not needed. IMO the gen set would be set up as a SDS and only the EGC should be ran to the transfer switch and transformer.

Rick
Looking back at my posts, I was sufficiently cryptic I didn't even understand what I was trying to say.:-?

See if this sounds better:
If the plant 480V system is grounded Y and is bonded at the main switchgear, and you use a 3W transfer switch to the gen:
Then the gen neutral needs to be connected to the plant neutral, and the gen frame is connected to the plant grounding system, and no neutral/ground bonding jumper at the gen. For this case the gen is not an SDS.

Even though not used, the gen neutral must be connected. Otherwise, when running under the gen a ground fault will not get back to the gen neutral and trip a CB.

cf
 
Last edited:

Cold Fusion

Senior Member
Location
way north
If the plant 480V system isn't grounded Y, but something different like corner grounded delta - then one would definitely not use the gen neutral.

cf
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
(( I may have misread the name plate at 12.5KVA because 12500VA divided by (208x1.732) = 34.69amps. I didn't even think about it because it's a big transformer. It may have been 125000VA but that would be 347amps. It's being fed by 1/0 copper from the 480v overhead buss. It's an old General Electric building and all of this equipment is original so I don't think they under sized it))
Maybe you did misread it, a standard transformer size is 112.5kVA.
Many times, old designers liked to run their transformers at 50% loading.
 

benaround

Senior Member
Location
Arizona
Anyone else feel this gen. is too small for the load ? 45000/480/1.73= 54 amps, gen.

supply. I mean just the 112.5KVA transformer @ 480vac side =135 fla., I think a good load

calc. needs to be done if it hasn't been done already. jmo.
 
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