Sizing a Generator for Industrial Facility.

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alphaX

Member
Hello, would appreciate if anyone can suggest where I should look at while sizing a generator set for an industrial facility. We have a meter connected accross the main breaker and it reads both appaent and real power. So should I size the Gen set according to the Peak apparant power or the peak real power. The meter is currently reading the peak apparant power as 700 and the peak real power as 615 over the last three months.
Thanks,
AlphaX.
 

dahualin

Senior Member
Alphax,

First, is this generator for emergency circuit or for power back-up?
Second, do the load calculation, treat the generator as a power service.
Third, If you know any local generator dealer/representative, talk to them and tell them the total load you calculated. They shall be able to size the generator for you with their software.
 

bsh

Senior Member
generator sizing

generator sizing

Most of the major gen manufacturer's have on-line sizing calculators. These take into account the staging of the equipment if it all doesn't need to start at once. Some include options for motor starting based on across-the-line, wye-delta, VFD, etc. Look at the Caterpillar, Kohler, Generac websites.
 

alphaX

Member
Thanks for the replies. It is a back up generator in case utility power fails for the whole facility. The whole facility with Three phase load equipments, HVAC systems, Offices and everything pulls 700 peak apparent power and 615 peak real power according to the SQG microligic Metering device Connected in the MAIN section of the switchgear. From the ATS it will go directly to the main switchgear. I thought I would look at the apparent power which is the power supplied by the utility. Would appreciate any feedbacks.
Alphax.
 

coulter

Senior Member
I would recommend a copy of IEEE 446 Emergency and Standby Power Systems for Industrial and Commercial Applications. The standard is 12 years old, but the principles are still good.

The peak power and pf are definitely important. However, another issue is starting large motor loads. I don't know if your peak reading meters are true peak, or a billing type 15 minute sliding scale. If 15 min sliding scale, then you are not seeing a true picture of the motor starting. One mfg suggests .5hp/kw.

Humm, I just made the assumption your load was lagging pf. Maybe it's not - if leading yu really need to let the gen mfg know. Most gensets don't deal with leading pf.

Don't forget to add the gen hotel loads. External cooling fans, building heat and lights, fuel pumps.

I tend not to load gensets up past 80% plus any needed capacity for motor starting.

Don't forget you will need a fuel tank. 500kW continuous is 800gallons/day. Since you are looking at a gen, which is not UPS, this tells me your outages are frequent, long, and expensive. Do a risk analysis before you buy a little (<5000G) tank

I don't tend to trust on-line calculators. The first priority of these calculators is to sell machinery. I figure they are about as truthful as a car salesman.

From what you have told us, a rough guess is a 1000kW unit, maybe $2,000,000. That's a serious enough project I would get some specialized help.

carl
 

alphaX

Member
Carl thanks for the input. The peak meter readings are true peak. The only thing I am worried about is the Apparant vs real power peaks over the three months periods that the SQD micrologic meter is showing. For a 615 real power peak load isn't a 1000KW a bit bigger. I was thinking of a 750KW set and that's where the apparant power peak issue came in.
AlphaX.
 

coulter

Senior Member
Maybe 750kW is enough, don't know - Here is where the analyze part starts.

Your power factor is ~.87 (apparent power)/(real power) = pf

And if it is lagging you are ok. Most gens are rated for .8pf lagging. So a 750kW is good for 937kVA.

But you are still looking at $1.5M. You really need a little closer engineering support.

carl
 

dbuckley

Senior Member
A very real issue is the size of the largest step load(s) compared to the overall genset engine rating. If the step load is relatively too big it'll underspeed the genset, whereupon the genset control will stop the set. Game over.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
No offense AlphaX, but if you are needing to ask these questions, you are already in over your head.

Your options: Hire an engineer knowledgeable in this area, or get a manufacturer on board, they are usually more then willing to help you figure it all out.
 

adavey

Senior Member
Location
New York
I would recommend adding 25% to the peak demand for sizing your genset (for future expansion). Also, the ATS should be installed after your Main Switch. Do you plan to use a 3-pole or 4-pole ATS ???????
 

alphaX

Member
Thanks much for everyone's input. "Adavey" what is the advantage of having the ATS after the main Switch? Also would appreciate if you could expand on the 3pole Vs 4pole ATS. I was planning for a 3 pole ATS.I thought you get a 3 pole ATS if you are under 1000KW.
Alphax.
 

alphaX

Member
Thanks a lot for the reference link, Adavey. Yes I will be using a service entrance rated ATS. Again is there a problem to put the ATS before the MAIN SWITCH?
AlphaX.
 
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