Generators running a machine shop?

[fastline]

I work in this space so I got tasked or rather asked about this. The reason I'm here asking is I want to hear any possible concerns or downsides here such as frequency regulation, regenerative drive backfeed, etc. Really anything that could possibly be a concern.

For info, most machines with any HP over 10 would be VFD but if you guys don't know CNC land, we accelerate FAST! Less than 1sec and constantly. I can't say I would know how to exactly size a generator to ensure solid operation, but also knowing that oversizing, especially with diesel is a big no-no.

But on that subject, I don't know if diesel or LP would give better frequency regulation? Hopefully enough mass to grunt through?

And for sizing, probably 2-3 machines for now with est very full load of 75kw. So probably targeting a 60-100kw generator. Keep in mind these machines can reduce loads and the goal was set to sort of see how much can be run, and consider upgrading to bigger later.

 

[synchro]

Since generators typically present a higher source impedance than a POCO supply of similar kVA capability, nonlinear load currents may develop relatively higher harmonic voltages when on a generator. Delta-wye drive isolation transformers on VFDs, for example, could help block harmonic currents if there are other loads that are sensitive to voltage harmonics.

 

[DBill64]

Is this in a place completely devoid of any power, or do you just not have a 3-phase service? If you have a fairly decently sized single phase service, you could also look into perhaps utilizing rotary phase converters? North American Phase Converter makes a 100 Amp model, and American Rotary has a similar offering. You could either do individual smaller units for each machine, or try to go large and cover multiple units with a single converter. They claim these are pretty good for CNC.

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[JoeStillman]

The generator manufacturers provide sizing software that allows you to evaluate all kinds of motor loads like ATL, Y-Δ, 6-pulse or 12-pulse CT/VT VFDs. I have used the Cummins one for years, but there's also MTU, Rehlko and Generac. Your local sales rep will hook you up or even run it for you.