Question generator having rating of 500kva, 450kva and 369kva yellow highlighted.

[hhsting]

Below generator cutsheet shows three different rating 500kva, 450kva, 369kva.

Plans I have show 400kw generstor. Does this mean the generator is 500kva, 450kva or 369kva? Or does that depend on fuel source?

 

[petersonra]

It means what it says. Under different conditions and fuel it has a different rating.

 

[infinity]

The power factor is .8 so a 500 kVA generator has an output rating of 400kW when used for standby with NG. LP ratings are lower.

 

[kwired]

Shouldn't rating be higher with LP than with NG?

 

[infinity]

Shouldn't rating be higher with LP than with NG?

Not according to those specifications.

For small generators run on gasoline the output is higher than NG.

 

[hhsting]

What kind of fuel is LP gas (vapors)? What is the difference between LP gas vapors and natural gas?

 

[kwired]

Not according to those specifications.

For small generators run on gasoline the output is higher than NG.

All I am seeing is specifications for LP and NG though? Switching to run on gasoline wouldn't be a simple field modification

 

[kwired]

What kind of fuel is LP gas (vapors)? What is the difference between LP gas vapors and natural gas?

Natural gas is what is typically piped in by gas utility companies, is primarily methane.

LP gas is commonly known as "propane" and is compressed and liquified and usually stored in container(s) on site rather than piped through utility lines.

 

[infinity]

All I am seeing is specifications for LP and NG though? Switching to run on gasoline wouldn't be a simple field modification

That's why I said small generators. Gasoline in no way pertains to this installation. Does using LP usually yield a higher output than NG?

 

[LarryFine]

Does using LP usually yield a higher output than NG?

Normally, yes, because Propane has a higher energy density than natural gas.

 

[synchro]

Shouldn't rating be higher with LP than with NG?

Not according to those specifications.

For small generators run on gasoline the output is higher than NG.

The generator posted by the OP is very likely turbocharged and optimized for natural gas. Natural gas has a R+M/2 octane of 120+, vs. the 104 of propane. And so to run on LP gas the boost would have to be reduced and the timing retarded, which will result in less horsepower.

Unless optimized to run on NG exclusively with a higher compression ratio and optimized spark timing, small naturally aspirated engines will produce less power on NG than gasoline. The higher octane of NG is associated with a slower burn rate, but that will actually result in less power than with gasoline if the timing is not advanced appropriately.

 

[kwired]

When you get into units of this size I would expect them to be optimized for the fuel type you want to use, I guess I can understand same engine may not produce as much power on one fuel vs another without some modifications, but why purchase a 500kVA alternator yet only connect it to a prime mover that can only produce 369? If you want to use LP why not order one with a prime mover that can produce 500 or can be optimized to run at that capacity?

 

[infinity]

All of the large generators that we install have a power factor of about 80% so the design just takes that into account when they specify the generator size. If we need 400kW they spec a 500kVA generator.

 

[kwired]

All of the large generators that we install have a power factor of about 80% so the design just takes that into account when they specify the generator size. If we need 400kW they spec a 500kVA generator.

You do that because of alternator specs, the prime mover only sees kW.

Same prime mover may have different kW output rating if fuel type is changed.

Any applicable kVAR is due to current only seen between the alternator and the load.