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Diesel engine for genset

Diesel engine for genset

Diesel engine for genset

I am give a task to build power unit. I have engine rated for 74 HP and alternator is rated for 75 KW. Can someone help me to determine how to calculate engine sizing I need for alternator rating? What will exactly happen if I use 55 kw rated diesel engine to run 75 kw rated alternator? Does it mean at Max engine RPM, I will not have rated output from alternator?


RE: Diesel engine for genset

In a nutshell, yes.
The alternator is able to support a load that the engine cannot; if this is attempted, speed will drop and a breaker will open and/or the engine will stall.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

RE: Diesel engine for genset

There is no problem with doing that as the alternator will run cool and be able to supply low power-factor loads easily. You would, however, need to limit the alternator output. I'd suggest you name plate it to what the engine can actually supply reliably and then you enforce that with the appropriate circuit breaker which is a needed item anyway.

You can figure out the actual available power by assembling it all then instrumenting the engine to see any pertinent quantities like exhaust temperature, oil temperature, and water temperature then loading the generator with 80% of the engine rating.

Run at that point until thermal equilibrium is reached then add a few more kw load. ~2kW? Wait for stability again. Do this up to 95% of the engine rating. Do not bother exceeding the engine rating as even thermal equilibrium doesn't mean the piston rods and crank are capable of exceeding the design output.

Keep in mind that the auxiliary engine loads often are not included in the engine's ratings. Things like the engine alternator, water pump, and any cooling fans. Also keep in mind that the alternator output doesn't include its own excitation power. Hence you want to start down around 75~80% which may be all you get.

Keith Cress
kcress - http://www.flaminsystems.com

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