generator size

[MBLES]

i have a customer that wants to size a generator for this epuipment. They cant get [permanent power at this time so this is best option for them per them. I am trying to help them determine the size of generator needed. The FLA is based on Table 430.250 All 3 phase 480 I am not sure how to add the 120v loads. If you guys dont mind I need a hand. They do mention PF is 70% but Im not sure where they are getting that number.and first 5 motors do have VFDs


1. 200hp 240a x 125%= 300a Largest Motor add all remaining flc
2. 200hp 240a
2a. 100hp 124a
3. 90hp 124a
4.90hp 124a
5. 50hp 65a
6. 50hp 65a
7. 40hp 52a
8. 20hp 27a
9.20hp 27a
10. 20hp 27a
11. 3hp 4.8a
total 1179 amps

not to mention

1. 2.3 hp 120v 24a
2. 5.6 hp 120v 56a
3. 5.6 hp 120v 56a
4. 5.6 hp 120v 56a

would this be added to the load at the end? they will need xfmr for 120v but just trying to figure size generator.

not to mention 120v

 

[iceworm]

You have a non-trivial application. If the gen is purchased, and you have under-sized, you're hosed. So I would be getting the onelines and all the panel schedules. This is big enough there really should be stamped drawings. Get them.

Look for non-coincident loads.
For example, the 200HP are doubled, and the 90HP, and the 50HP. If any of those are installed spares, you can delete one from the calc.

The owners speced, .7pf - believe them until shown different.

So, with what you have:
(1179A /.7 pf ) x 480 x 3^.5 = 1400KVA

For the small loads, just add the kVA, maybe add 5% for transformer losses.
Don't forget any hotel loads:

Heat
lights
office
shops​

If the plant is built, all the transformers and panels for the hotel loads should be there. If not ....

And it looks like you have a continuous/prime rated application, so recommend either get a prime rated gen, or if not, don't load past 80%

Non-prime/non-continuous
1400KVA/.8 = 1750KVA + hotel load. You are in the 2MVA range

2MVA at 480V is 6-500kcmil/phase. Consider equipment, process, and generator locations. You could be looking at 4160V generation, and stepdown transformers

Now consider off peak loading:
If the process is cyclic, as in maybe they don't run at night, you may have to spec two or three generators. A lot of generators don't like to run lightly loaded. So if the load is cyclic, you may have to shut one or two down during the lightly loaded times - Powerplant operator, paralleling gear.

There maybe air permit issues. I can't advise you on that part.

Check the economics on a rental.

You are going to need good vendors for:
Generator(s)
package assembler (gen auxiliaries, sync equipment,

Probably an engineer(s) (PE) for the electrical, and air permits if needed.

And maybe you can rent one delivered on a flatbed and connect it with dump truck load of type W.

Like I said - It is non-trivial, maybe $5Million

Good Luck. Let us know how it turns out - it is interesting.

The Worm

 

[MBLES]

let me clarify a little. Customer wants a temporary generator to operate some equipment with all these motors. The equipment is temporary for 3 or 4 months. The equipment is portable. There is no need for anything else but maybe a container that will need some general purpose 120v outlets and other 120v loads on list other than that its only going to operate the equipment. I was looking for help on how to size generator. I assumed what I posted was sufficient info for question.

 

[JFletcher]

1200 amps or so at 480 volts is on par with a smaller (10MGD) wastewater treatment plant.

You need to determine the nature of your loads, whether they are continuous, whether some of those Motors are non coincidental, such as a lead lag set up, and so on.

as the worm wrote, If all of these are on at one time, you were looking at a generator (s)in the 2 MVA range, which will be something like a 20 cylinder EMD or a pair of cat 16 cylinder generators. With the currents possible, you may very well have to generate at 4160 and step it down to 480.

I would Google something like industrial power solutions or industrial size generator rentals, and call a company that specializes in these types of rentals and installations.

 

[MBLES]

1200 amps or so at 480 volts is on par with a smaller (10MGD) wastewater treatment plant.

You need to determine the nature of your loads, whether they are continuous, whether some of those Motors are non coincidental, such as a lead lag set up, and so on.

as the worm wrote, If all of these are on at one time, you were looking at a generator (s)in the 2 MVA range, which will be something like a 20 cylinder EMD or a pair of cat 16 cylinder generators. With the currents possible, you may very well have to generate at 4160 and step it down to 480.

I would Google something like industrial power solutions or industrial size generator rentals, and call a company that specializes in these types of rentals and installations.

I understand. I am just curious why the customer provide the requirements in KWH vs the FLA on table 430.250 I did see where the customer did send the same info but in KWH to generator supplier and they specify a 1000/1250kva generator. I thought we were to use table.

 

[iceworm]

let me clarify a little. Customer wants a temporary generator to operate some equipment with all these motors. The equipment is temporary for 3 or 4 months. The equipment is portable. There is no need for anything else but maybe a container that will need some general purpose 120v outlets and other 120v loads on list other than that its only going to operate the equipment. I was looking for help on how to size generator. I assumed what I posted was sufficient info for question.

Okay - try this
snip
Following JF's post:

The owners speced, .7pf - believe them until shown different.

So, with what you have:
(1179A /.7 pf ) x 480 x 3^.5 = 1400KVA
For the small loads, just add the kVA, maybe add 5% for transformer losses.

1500KVA is tight, but possible. Part of the current you listed for each motor is reactive and is counted twice when the .7pf is used.

Consider equipment, process, and generator locations. You could be looking at 4160V generation, and stepdown transformers

Good Luck. Let us know how it turns out - it is interesting.

The Worm[/QUOTE]

 

[iceworm]

I understand. I am just curious why the customer provide the requirements in KWH vs the FLA on table 430.250 I did see where the customer did send the same info but in KWH to generator supplier and they specify a 1000/1250kva generator. I thought we were to use table.

You lost me. I didn't see any KWH numbers, just saw amps and nominal voltage. However, I don't see why you would need KWH. You do need to get the loading - and for motors that will be in amps. But you will have to translate to KVA - because generators are sized in KVA.

1250 KVA sounds small, unless it is a prime/continuous rated.

the worm

 

[topgone]

I understand. I am just curious why the customer provide the requirements in KWH vs the FLA on table 430.250 I did see where the customer did send the same info but in KWH to generator supplier and they specify a 1000/1250kva generator. I thought we were to use table.

My calcs came out the same as what your customer speci'ed (assuming the motors are started in a staged manner). Worry about the possible voltage dip when large motor starts. If the facility is sensitive to voltage flickers, please choose a bigger genny.

 

[JFletcher]

I understand. I am just curious why the customer provide the requirements in KWH vs the FLA on table 430.250 I did see where the customer did send the same info but in KWH to generator supplier and they specify a 1000/1250kva generator. I thought we were to use table.

Not sure why the customer provided kilowatt hours... I would want kVA or nameplate data for an installation like this.

Just curious, what is this installation? With its temporary nature, is this equipment going to be used for mining or treating mine waste? There's no HVAC/ventilation or site lighting load to take into consideration?

I know your first five or six largest Motors are vfd, so I'm surmising that's why you're not really having to take into account in rush, and also the rather poor power factor. The other motors, they are started across the line?

While the table is helpful, you really need to know all of the operational parameters to make a decision. The job specs your prospective client sent to the generator people may have been more detailed, or perhaps failed to include everything.

Short story, 20 some odd years ago I worked at a Wastewater Plant undergoing an upgrade. Its main power supply was a 2000 amp 480 volt service, with a single turbine generator rated at 2 megawatts. Everything worked well, except at night time, when the site lighting came on, a 156 kilowatt dead load, it caused the 250 hp vfd driven centrifuge to trip offline on under-voltage, and occasionally would also knock off an aeration blower (350hp). That was on utility power, a far stiffer supply than the generator.

The criticality of everything needing to run uninterrupted 24-7 would or should have something to do with the generator choices well. While the table is a good start, I would definitely consult engineering on a project of this magnitude.

 

[MBLES]

You lost me. I didn't see any KWH numbers, just saw amps and nominal voltage. However, I don't see why you would need KWH. You do need to get the loading - and for motors that will be in amps. But you will have to translate to KVA - because generators are sized in KVA.

1250 KVA sounds small, unless it is a prime/continuous rated.

the worm

I left out alot of information mainly because I havent seen the equipment or know the processes. I also didnt know what to make of the information share to rental company. I will meet customer tomorrow. I know its a dredging machine that will set up near ports and ship channels to move sludge and or sand. The equipment is supposed to be portable and permanent power isnt possible, well at least thats what customer is saying. That is why a generator will be needed to support the equipment. I am not able to down load because its part of an email and I am not able to share,because computer wont let me. I hope this makes sense. Each motor listed on information proivided to generator rental company is list as such

The information shared to generator rental company goes as follows for each motor listed per their HP example:

equipment? HP? soft start or vfd? Start UP Sequence ? Voltage? Phase? PF? KWH Required? Assumed Average % ? KWH Required?

watet treat 100HP VFD YES 480v 3 70% 67.2 KWH 60% 40.3 kwh


The total listed KWH once you add all motors listed is 692 KWH with 60% applied is 395 kwh( at least thats what they have written to generator rental. I am not sure what is continuous, non coincidental, back up motors or systems, and or if they all work at same time. I will find out tomorrow. I hope once I get more information so I can see if you guys can help to determine if the generator will be to small or just right for application. We will be required to wire the equipment I am just trying to establish if generator is to small or just right. I appreciate all the help so far.

 

[MBLES]

Okay - try this
snip
Following JF's post:

The owners speced, .7pf - believe them until shown different.

So, with what you have:
(1179A /.7 pf ) x 480 x 3^.5 = 1400KVA
For the small loads, just add the kVA, maybe add 5% for transformer losses.

1500KVA is tight, but possible. Part of the current you listed for each motor is reactive and is counted twice when the .7pf is used.

Consider equipment, process, and generator locations. You could be looking at 4160V generation, and stepdown transformers

Good Luck. Let us know how it turns out - it is interesting.


I understnad the reactive part but why is it counted twice when 70%PF is used?