What generator size needed to stagger start and run (2) 50HP motors?

[rrc14]

What size diesel generator would be needed to stagger start and run (2) 50HP motors? Reference uploaded motor nameplate. We have a 100kW geneator that does fine starting and running a single motor, however, when we attempt to start the second motor the motor already running quits running :?. Any general guidelines for sizing generators for electric motors?

Thanks,

 

[ptonsparky]

Try to find a different source for the control voltage. That is what was dropping out on a large motor we had to start with a generator a few years ago. We told them one start a day and leave the sucker running, loaded or not.

Best solution is a properly sized Genset.

Duh that's good, huh? Tell you to do what you already know you need to do.:slaphead:

We had a small one sized recently for a submersible well. Well mfg suggested the gen itself be sized 2 times the KVA of the motor.

 

[Dennis Alwon]

100 Kw generator should work

 

[ptonsparky]

100 Kw generator should work

Ah, but it doesn't. Time to call the mechanic for a tune up?

 

[Jraef]

Quick rule of thumb:
kW of generator = 3X the HP, if you want the VD to be less than 5% on startup. You are at 2X with one motor, so your VD is already likely more than 5% at startup, but not enough to cause your starter coil to drop out. But when you start the 2nd motor, it is. That's why using a separate control power source would likely allow that generator to work, but putting a UPS on it might work too.

If you are OK with upping the size of the genset, I would go with 150kW, because knowing that one starts with 100kW, the first motor is going to consume the first 50kW after it is running, so you will have 100kW left over and you already know that worked for you.

 

[kwired]

soft start or VFD may let you start second motor while first one is running.

 

[Jraef]

soft start or VFD may let you start second motor while first one is running.

If you already own the generator, I would go this route for sure.

 

[mayanees]

Quick rule of thumb:
kW of generator = 3X the HP, if you want the VD to be less than 5% on startup. .

.. with all due respect Jraef, I submit that the 5% number would apply to the running voltage drop (VD), which would be consistent with NEC 695.7 that allows 15% starting VD and 5% for 115% of fla - for fire pumps. I do agree with the 3X number...

 

[ptonsparky]

If you already own the generator, I would go this route for sure.

Depending on the Mfg and minor details like enclosure, line and load reactors, etc, etc, $2500 is a lot lower than I expected to see.