What size generator?

[Hankdog1]

Need a generator to run a 165HP and 2 150HP 3 phase electric motors. Any of you guys got any ideas on the size I would need to accomplish my task?

 

[Stuart in MN]

What voltage? I assume 480vac. Are the motors started across the line, or do they have reduced voltage starters, soft starters or VFDs? Can they be started sequentially or do they all start at the same time? Are there any other loads besides the motors?

I have a Caterpillar generator sizing program on my computer at work, I can run the numbers tomorrow if you fill in the blanks above. I can tell you it's gonna be a big one.

 

[930dreamer]

A huge one, what are the electric motors powering? Sounds like 300-400 amps or more?

 

[Hankdog1]

They are hydraulic test benches and no they don't have to be started at all the same time. The monster 165HP motor is more then is needed but when your buying the stuff for next to nothing you can't complain. No soft starts or VFDs.

 

[Stuart in MN]

No soft starts or VFDs.

That's going to be the tough part...starting motors that big across the line takes a BIG generator. I'll post a reply in the morning on the size requirements.

 

[A_Pmech]

My guess is it is probably significantly cheaper to build a diesel mule if you need to use it in the field.

 

[Hankdog1]

Nope nothing in the field. The kind of work I do with rebuilding hydrastatic transmissions I have to keep everything clean. Contamination is a killer when your working with piston pumps and motors.

 

[StaggeringGoat]

Good god. You'd need at least a 400KW generator...if not more. You can't get 3 phase from the power company?

 

[Hankdog1]

Yeah I could but I don't have the kind of cash laying around to have 3 phase ran to my shop. Heck I could buy land next to a 3 phase line cheaper then I can run it.

 

[StaggeringGoat]

Do you realize how much that size of generator will cost? And the fuel?

 

[Hankdog1]

Heck I don't have to run the thing for 8 hours a day just when I'm testing a unit. Besides my line of work folks pay to have things done right. Not to mention most of the distributors do a crappy job on the rebuilds. Seen stuff that has gave out after a week in service just because some yahoo hand tightened the bolts. All kinds of bypass how the heck it ever passed testing I'll never know.

 

[ishiboo]

Need a generator to run a 165HP and 2 150HP 3 phase electric motors. Any of you guys got any ideas on the size I would need to accomplish my task?

You're looking at probably at least 200kw just to run and start the 165hp alone, figure that's about 125kw plus you'll want a good margin for starting it/etc. It'll be a big unit!

 

[Steve from Socal]

I looked into a generator to run my puny 60 HP compressor and a few 20-30HP machines, you need at bare minimum 350KW gen. If you can get natural gas I would look for a gas generator.

Steve

 

[nehog]

With that size load, consider a (used) military surplus unit. Check eBay for examples, but for a large generator, I suspect you are talking about $30K or so for something that is good.

Personally I think you'd be better off replacing those electric motors with diesel ones.

 

[Stuart in MN]

OK, I ran the numbers through two sizing programs.

Assumptions:
480vac, three phase
Diesel power
Altitude 2000 feet (that's what I found online for Cedar Bluff, VA)
Ambient temperature 85 degrees F
Load #1 165hp started across the line
Load #2 150hp started across the line
Load #3 150hp started across the line
Motors started sequentially

The Caterpillar sizing program recommends a 500kw generator
The Cummins sizing program recommends a 400kw generator
In my experience the Cat sizing program tends to be a little on the conservative side, but in any case it's best to give the loads to the generator salesperson and have them determine what you need - at least this gives you a ballpark number.

As for the price, the installed cost of a new generator will probably be in the $80,000 - $100,000 range depending on size. Used will be less expensive, of course.

A 500kw Cat generator is about 150" L x 44" W x 83" H and weighs just under 8,000 lbs. This is without an enclosure - I don't have those numbers handy but the enclosure will add several feet to the length and probably another 1,000 pounds to the weight.

If it's something you only use intermittently, it may be worth considering a rental unit instead - the generator suppliers have trailer mounted generators they can bring out for short term use.

edit: someone else mentioned using a natural gas generator - smaller than about 100kw or so a natural gas generator can be a good choice, but when they get bigger than that they're more expensive than diesels and the cost goes up exponentially; in the 400-500kw range they are a LOT more expensive than diesels.

 

[Rte66Charlie]

OK, I ran the numbers through two sizing programs.

Assumptions:
480vac, three phase
Diesel power
Altitude 2000 feet (that's what I found online for Cedar Bluff, VA)
Ambient temperature 85 degrees F
Load #1 165hp started across the line
Load #2 150hp started across the line
Load #3 150hp started across the line
Motors started sequentially

The Caterpillar sizing program recommends a 500kw generator
The Cummins sizing program recommends a 400kw generator
In my experience the Cat sizing program tends to be a little on the conservative side, but in any case it's best to give the loads to the generator salesperson and have them determine what you need - at least this gives you a ballpark number.

As for the price, the installed cost of a new generator will probably be in the $80,000 - $100,000 range depending on size. Used will be less expensive, of course.

A 500kw Cat generator is about 150" L x 44" W x 83" H and weighs just under 8,000 lbs. This is without an enclosure - I don't have those numbers handy but the enclosure will add several feet to the length and probably another 1,000 pounds to the weight.

If it's something you only use intermittently, it may be worth considering a rental unit instead - the generator suppliers have trailer mounted generators they can bring out for short term use.

edit: someone else mentioned using a natural gas generator - smaller than about 100kw or so a natural gas generator can be a good choice, but when they get bigger than that they're more expensive than diesels and the cost goes up exponentially; in the 400-500kw range they are a LOT more expensive than diesels.

THIS is why I love this place - ask any question, ANY question you want, no matter how weird or obscure or ridiculous you might think it is, and someone here will be able to help you. Thanks Ryan, this site is just frickin' amazing.

 

[ishiboo]

OK, I ran the numbers through two sizing programs.

Assumptions:
480vac, three phase
Diesel power
Altitude 2000 feet (that's what I found online for Cedar Bluff, VA)
Ambient temperature 85 degrees F
Load #1 165hp started across the line
Load #2 150hp started across the line
Load #3 150hp started across the line
Motors started sequentially

The Caterpillar sizing program recommends a 500kw generator
The Cummins sizing program recommends a 400kw generator
In my experience the Cat sizing program tends to be a little on the conservative side, but in any case it's best to give the loads to the generator salesperson and have them determine what you need - at least this gives you a ballpark number.

As for the price, the installed cost of a new generator will probably be in the $80,000 - $100,000 range depending on size. Used will be less expensive, of course.

A 500kw Cat generator is about 150" L x 44" W x 83" H and weighs just under 8,000 lbs. This is without an enclosure - I don't have those numbers handy but the enclosure will add several feet to the length and probably another 1,000 pounds to the weight.

If it's something you only use intermittently, it may be worth considering a rental unit instead - the generator suppliers have trailer mounted generators they can bring out for short term use.

edit: someone else mentioned using a natural gas generator - smaller than about 100kw or so a natural gas generator can be a good choice, but when they get bigger than that they're more expensive than diesels and the cost goes up exponentially; in the 400-500kw range they are a LOT more expensive than diesels.

Ah, I read this as only one being running at the same time, not only one started. Ooops! 400kw sounds okay if they are staggered starting, the horsepower works to to 331kw.

That's going to cost you about $100/hr just in fuel, and with the price of the generator, if you're in an area that has 3-phase it will be far less expensive to install 3-phase service if you handle the inside wiring yourself.

 

[Stuart in MN]

Hankdog will have to confirm if all three motors are running at the same time or just one - if it's just one at a time the generator can be a lot smaller.

I agree it's worth checking with the local electric utility to see if a three phase service can be installed, but it will probably need to be at least 600 amps and probably 800 amps, so it won't be cheap, either. Also, they will probably require the motors be operated with soft starters or VFDs - most utilities don't want their customers starting motors that big across the line.

 

[Dickey]

We use a 440kw generator for our server room. It is a turbocharged GM 502ci natural gas rig that runs at 1800rpm. As I recall it set us back $75k for the generator and associated switch over gear.

Edit - just realized my above was silly as ours is only a 208vac 3 phase deal.

 

[Steve from Socal]

While the up front cost of a gas generator is higher, over the long term it is far cheaper to run. If a company needs that level of power on a constant basis then the generator will also need to be sized to run in its optimum range generally 50-70% load. The fuel cost are much greater than the initial buy in over a service life of a couple of years. Spending money up front to save much more over the life of the power plant is a valid consideration, let alone the logistics of feeding a powerplant this size on a constant basis.

Steve

 

[wnstwolf]

We are in initial phase of installing a new Cat 500kw unit here at work. Capital budget is 350k not including a fuel tank as that is close by from other equipment using diesel. This includes the gen set at about 100k, panel and switch gear at 50k and the rest installation and enclosure/slab/building to put it in.

 

[rlitman]

That's going to cost you about $100/hr just in fuel, and with the price of the generator, if you're in an area that has 3-phase it will be far less expensive to install 3-phase service if you handle the inside wiring yourself.

Not necessarily. If you're only running a few hours a month, you'll be paying only for those few hours of fuel, but if you have a 3 phase service installed, just turning them all on at the same time only ONCE, could leave you with an even more staggering bill, EVERY month for the following year, just because of the "demand" charges.

 

[Steve from Socal]

Not necessarily. If you're only running a few hours a month, you'll be paying only for those few hours of fuel, but if you have a 3 phase service installed, just turning them all on at the same time only ONCE, could leave you with an even more staggering bill, EVERY month for the following year, just because of the "demand" charges.

This is exactly why I am looking at a generator, a generator aint cheap BUT, it is far less costly than a huge demand charge for infrequent use. The OP should add a bit of the use profile on the generator.

Steve

 

[Stuart in MN]

While the up front cost of a gas generator is higher, over the long term it is far cheaper to run.
Steve

Not to get off topic, but while a 500kw diesel generator is going to cost around $100k, a 500kw natural gas generator may be $200k or more...that extra $100k would pay for a lot of diesel fuel. I do agree that the overall cost including fuel needs to be considered - if the generator is run continously over a long period of time, the payback on a NG generator will be faster.

 

[rlitman]

Not to get off topic, but while a 500kw diesel generator is going to cost around $100k, a 500kw natural gas generator may be $200k or more...that extra $100k would pay for a lot of diesel fuel. I do agree that the overall cost including fuel needs to be considered - if the generator is run continously over a long period of time, the payback on a NG generator will be faster.

Perhaps, but if it's used continuously, getting power from the grid will still probably be cheaper.

 

[tdkkart]

Perspective, generators are typically 2hp per KW, so we're talking 800-1000HP here. Probably looking at 40+ gallons of fuel per hour.

 

[Hankdog1]

I just need it to run 4 or 5 hours a week. I can get by with only using one test bench at a time but trying to keep in mind that one day the work might get to the point where I have to have them all running at once to get stuff out the door. The solution might be to just go smaller for the time being and keep an eye out for a used 500 kw genny. As for getting 3 phase ran I'm looking at several miles of new lines put in. Should be able to come across a decent deal on a used generator being in coal country where they have the same problem when mining up in these rather remote hollows.

 

[Stuart in MN]

Should be able to come across a decent deal on a used generator being in coal country where they have the same problem when mining up in these rather remote hollows.

I didn't think about that...there was that show on TV last year about coal miners, and one of the things I noticed was they ran their equipment off big generators. At least that means you probably have a few generator dealers in the area.

 

[Steve from Socal]

If you could get by with a two motor scenario as worst case then you could use a 300KW generator. On ebay there are several diesel and gas powered from 2 to 30 grand.

Steve

 

[east_tn_emc]

Wouldnt it be significantly cheaper and easier to just re-power the equipment that requires the 150HP and 165HP to be powered by their own diesel engines instead of electric motors?

I would think that you could get a couple of diesel engines in that HP range much cheaper than an 800-1000HP DG set.

 

[A_Pmech]

Still seems a lot cheaper to buy a $3k diesel engine and bolt it up to your existing hydraulic pump setup. Put some wheels under it and you have a mule you can take anywhere.

 

[Hankdog1]

Still seems a lot cheaper to buy a $3k diesel engine and bolt it up to your existing hydraulic pump setup. Put some wheels under it and you have a mule you can take anywhere.

Already have one of those but the power plant is a 350 V8 gasoline engine. Used it for years testing denison IVS units for Simmons Rand continuious miners. Now looking at going after bigger business which means bigger pumps and motors. I like building new stuff as much as the next guy but the problem is time. In the process of looking to upgrade my dyno to digital too. Got another 45 HP motor I've gotta build another smaller test bench out of. Got a bunch of buddies wanting to help me out with business just gotta get the rest of my testing equipment up and running. Also gonna have to add more machineing equipment over time most of that stuff the size I need is 3 phase. Time to just **** it up that it's something I'm gonna have to do regardless.

 

[MoonRise]

Hmmm, take fuel and turn it into rotary motion (diesel engine). Take rotary motion and turn it into electrical energy (gen set connected to the diesel engine). Take electrical energy and turn it back into rotary motion (electric motors to run hydraulic test bed). Take that rotary motion and connect it to some hydraulic pumps (to run the hydraulic test bed).

Or take fuel and turn it into rotary motion (diesel engine). Take rotary motion and connect to hydraulic pump(s). Eliminate at least two 'energy conversions' and their associated efficiency losses.

If you don't have the electrical infrastructure in place to run those pretty big electric motors, then it sure seems like repowering the hydraulic pumps to use an engine instead of electric motors would be the way to go.

Your call and your choice.

[ rough rule of thumb calc: IC engine usually needs to be ~twice the 'HP' as an electric motor, because of torque curves and whatnot. So 165 hp electric motor needs ~320+ hp engine driving the gen set, that's 240 kw not counting electrical efficiency losses. Add in two 150 hp electric motors and run them all at the same time and I come up with a rough calc of 620 hp aka 465 kw on the gen set. So 400 kw seems a bit 'light' to run all three electric motors at once and 500 kw will still be pushing that gen set pretty hard to run all three electric motors at once. My rough calc for a 'rated' 500 kw electric output says the engine to spin that generator is going to be around 850+ hp shaft output (allowing an ~80% efficiency rating from rotary input to electrical output of the gen set. That's not a small engine. Well, it is smaller than a marine diesel or a PoCo power plant operation, but still pretty big. My rough calcs are in line with the above poster's calcs as well. ]

500 kw gen set on GovDeals, 1986 Cat with 1521 hrs listed, bidding is up to ~$13k right now

http://www.govdeals.com/index.cfm?fa=Main.Item&itemid=351&acctid=1524

~9000 lbs of gen set there.

Some used 500 kw Cat gen sets here (no endorsement, either for or against, etc, etc)

http://www.rockanddirt.com/search?l0=equipment&l1=CATERPILLAR&l2=500 KW&l3=generators-electric-power

~$80k - $95k

Used 1986 500 kw Cummins skid-mount gen set, ~$35k bid/price

http://www.rockanddirt.com/equipment-for-sale/CUMMINS/500 KW/invnum=34337498

Cummins 'rental' gen set, 500 kw standby and 455 kw 'prime' power (Model C500), listed as gulping fuel at 30 gph at full load and 11 gph at 1/4 load. See the Cummins Power website.

 

[Hankdog1]

Thanks guys gonna keep my eye out and put the word out what I'm looking for. Be nice if people would pay me for all the **** I've done over the years. Could just buy a new place with 3 phase and not have to worry about this step in the process.