Generator for 75 H.P. motor 2

[Lazerdog]

Hey everybody

I've got a customer who needs a generator to run a 75 H.P. electric motor at prime. The electric motor is rated 440 V, which I assume means he needs a 480 V L-L. I'm looking for a product to purchase that would reduce the size of generator that he'd need. What would you guys suggest? A soft-start or a VFD?

Can anyone link something to point me in the right direction?

Thanks

 

[waross]

I have had experience with a lot of residential installations with a lot of big air conditioning loads.
Some have Permanent Magnet Generators fitted and some don't.
My observations;
The PMG fitted sets have less voltage dip and less flickering of the lights when starting a large A/C when the size of the A/C is well within the capability of the set.
Starting larger motors, where the set is marginally sized will often drag down the frequency of the set. Once the frequency drops more that 3 to 5 Hz. on a modern Automatic Voltage Regulator, the Under Frequency Roll Off feature becomes active. The UFRO starts to drop the output voltage in proportion to the drop in frequency. Even though the PMG is supplying adequate voltage to the AVR to maintain the output voltage, the UFRO feature of the AVR is dropping the voltage to shed load and give the engine a chance to get back to speed. Most AVRs now supplied on new sets have UFRO. As well as shedding momentary overloads, AVRs with UFRO do not burn out if the generator is operated at reduced RPMs. Any one who has been around older diesel gen-sets will remember the warnings to turn off the AVR before stopping the set. Most of you will also remember changing AVRs when the operator forgot to turn off the AVR when he ran the set at low RMs for some reason.
I have found PMGs to be more useful starting smaller motors that big motors. (Relative to the size of the set.)
Once the motor starting load slows the generator more than 3 to 5 Hz. the PMG becomes less helpful.
If a generator is not powerful enough to start a motor with a standard AVR it will not be able to start it with a PMG.
That said, I spec. PMGs whenever The customer is willing to pay for them.
respectfully

 

[itsmoked]

Interesting stuff hogdawg and waross. Now I know what the UFRO does.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com