Testing Generator Sizing Calculator - Need Help Testing

[jar546]

I think this one is good and self explanatory unless there was something lost in translation when i put it on the server. Check it out and let me know.

Generator Sizing Calculator | The Building Code Forum

 

[chris kennedy]

It doesn't take into consideration motor starting current.(LRA)

 

[Gregg Harris]

would that not be the input kva?

 

[chris kennedy]

I recently wired a piece of industrial equipment with a 350hp motor and a 50hp motor.
So that's 465A or 386 kVa. I'm currently running this off a 500 kw generator. No problem right?

My 500 kw generator workes out to 602A. Now here is why motors are of concern.

The 350 HP motor is on a soft starter. It draws 1604A for 10 seconds before soft start bypass engages and the motor draws 401A.
Generators have to have the "balls" to start these kinds of loads.

 

[jar546]

The 350 HP motor is on a soft starter. It draws 1604A for 10 seconds before soft start bypass engages and the motor draws 401A.
Generators have to have the "balls" to start these kinds of loads.

I think that is a conversation to have with the generator manufacturer based on that fact. Sizing a generator is rather straightforward until you have an issue like this. It sounds to me like this motor should be on a VFD to reduce the inrush current and not just a soft start. Or, you can adjust that soft start. That is too much current for a motor with a soft start.

 

[jar546]

OK. Some changes made to the calculator for informational purposes.

 

[Gregg Harris]

I think that is a conversation to have with the generator manufacturer based on that fact. Sizing a generator is rather straightforward until you have an issue like this. It sounds to me like this motor should be on a VFD to reduce the inrush current and not just a soft start. Or, you can adjust that soft start. That is too much current for a motor with a soft start.

I would agree VFD makes for a better choice considering the size.