stand by generators

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steveng

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Texas
i have a 28 kw 480/277 3 phase standy by duty diesel generator, what maximum load in amps, can i put on my generator?:smile:

the original nameplate came as
kva 35
kw 28
volts 220/127 amps 92 3 ph
100 amp brkr

however, it was changed to 480 3ph,
what formula can i use to determine the rated load for this generator? it will be used
as stand by duty only.
 
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I would say that 28kw is the max load as you stated. The real (continuous) rating will be different more than likely. I would think some kind of nameplate or something would be on generator somewhere.
 
Probably between 150 and 200A...but not for very long :)

Seriously, this generator probably has several ratings.
1) The _continuous_ current rating of the alternator
2) The _motor starting_ current rating of the alternator, which basically uses the mechanical intertia of the system. Maintain this current for an extended period, and a breaker will trip or the engine will stall.
3) The _overload_ rating of the alternator (and prime mover), a _time limited_ rating
4) The mechanical output rating of the prime mover, which is the ultimate limit on the electrical output. This will then have different ratings depending upon class of service, for example the engine will have one rating if used 24/7 for 'prime power' and a different rating for 'emergency service'

-Jon
 
steven -

Usually 480V or 3ph generators are rated in KVA at a specified power factor, usually 0.8. However, if it is rated in kw, then you will need the specified pf.

As bb said, check the nameplate.

carl
 
I would reccomend a trip to cummins power generation, Kohler or Cat Diesel generators for a little background. Generators live by the following rules:

KW is a function of Prime Mover (the motor)
KVA is a function of apparent power (the Alternator)
To estimate what maximum amperage you can design around it is often safe to assume a .8 power factor.
This translates to 28kW/.8 or 35 kVA.
@ 480V this results in 35000/480*1.732 or roughly 42A.
As mentioned earlier, this doesn't mean you can start a 40 HP motor across line. you will peobably exceed the allowable voltage drop and frequency drop. This usualy causes protective relays to drop the motor off line. It will at least cause some serious contac chatter.
Hope this helps.
 
thanks for your help guys

thanks for your help guys

i am defering to the senior electricians, engineers hoping to glean a little wisdom from the ones who should know.;)
 
if the loads are mostly resistive / inductive, you can probably load the generator at its full capacity.

however, motor loads are a different story. the bigger the motor load, the greater the cahnces of a visible voltage sag if the motor starts when the lights are already on
 
thanks again!

thanks again!

thanks for the responses, this generator only supplys lighting, and receptacle loads. as of now , the load on the generator is approx 10 11 14,
but, we will most likely add some additional load later on.

it is on automaticlly when utility power fails.
 
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