Loading a generator, KVA vs KW

[mark32]

Hey guys,

I know someone will shed light on this in short order, but here goes. I am tasked to perform a monthly load test on a standby generator. The specs are as follows: 850 KVA, 680 KW, 480 VAC, PF .8

During the test, the readout on the Generator's screen shows the load varying between 240 and 250 amps. On a subsequent screen, it shows the load being supplied is approximately 30% of the gen's capacity, which is good because my employer wants the gen loaded to a min of 30%. However, when I fill out the paperwork for the test, it states a load of 307 amps is 30% of the gen's capacity, hmm. So it appears the person who wrote up the test sheet is using KVA to derive the 307a figure (850kva/480/1.732 = 1022 amps*.3 = 307 amps), but the generator is using KW to derive it's % figure (680kw/480/1.732 = 818 amps*.3 = 245.4 amps) So, which formula would you say is the correct one to be used here?

 

[d0nut]

The correct requirement is 30% of the nameplate kW rating for diesel generators or loading that maintains the minimum exhaust temperatures as recommended by the manufacturer. The requirement comes from NFPA 110.

 

[mark32]

Thank you sir,

Yes, I was required to take exhaust temps as well. So, the paperwork's figure is incorrect, I will make the appropriate corrections. Thanks d0nut!

 

[winnie]

If your employer wants the _alternator_ tested to 30% of its capacity, then the paperwork is correct. Remember that the customer gets to request whatever they want to request, as long as the specification is on the back of a large enough check.

I suspect that @d0nut is correct and that what your employer actually wants is to meet the NFPA requirements, and that the paperwork is not correct. But when you have such a discrepancy, it pays to double check your understanding rather than guessing what your customer/employer wants and getting it wrong.

-Jonathan

 

[mark32]

Thank you Jonathan for your input. I'm actually running a number of generators for this building, and I've come across other paperwork discrepancies as well. So, it wouldn't surprise me that the author of the document in question got this wrong. I'll discuss it with my supervisor and let him discuss the issue with the guy who put these checklists together. Thanks!