you have a problem that is much bigger than I work on. But on a large
motor heavy starting loads problem, we used an extra capacitor on the DC
bus of the frequency drive. the drive on its own greatly reduced the start
surge, if the load can be started slowly. If the motor must ramp up
quickly the voltage would drop and the capacitor reduced the bump on the
line. This was a few years ago but we put a 200 HP drive on a 100 HP motor
and added the extra capacitor. Another trick on a different job was to run
a 3 phase motor with a flywheel and start this motor slowly when the motor
that had to start rapidly the running motor acts as a frequency
stabilizer and dumps it energy into the rapidly starting motor. again this
was maybe 15 years ago. these kluge solutions were applied when the
inverter could in no way handle the surge and would kick the inverter off
the line. Another solution used by Catipiller they had a unit that could
give 3000 amps 480 v0lts for I think 30 seconds running a motor as a
flywheel for UPS giving the generator set time to start. Check with
Catapiller. again another project we clutched the running motor to the
load to start the load fast and not have to face starting current. One
last comment we had a 5000 HP motor to start a very heavy load, this motor
had a hydraulic coupling that filled with oil to control the motor load.
But I think a speed drive is more practical. And there are regen drives
also.
There are some other kluges that can be applied, good luck, sorry if this
is of no value.
On Wed, Apr 25, 2018 at 2:36 PM, Ray wrote:
> Greetings Fellow Wrenches;
>
> We are consulting on a power system for a large off grid facility that is
> currently operating on a 1500 kW gen set. The loads are enormous for
> normal off grid: in the neighborhood of 600 amps continuous at 480 v 3
> phase. Surges are close to 2000 amps, but we are working on control
> programming to bring that number down substantially. That is due primarily
> to a 250 Hp motor start. (that's not a typo!). EPA and local regulations
> are dictating that the current generator be retired in the near future.
> Grid power is a possibility, but we need to offer a viable off grid option
> as well.
>
> My question to the group: does anyone have real off grid experience with
> large format battery based inverters? I've heard of some micro-grid
> systems running in Haiti on Princeton Power inverters, and Dynapower has a
> 250 kW inverter that has a "grid forming" mode. As we all know, it is
> easier to make claims in spec sheets than to deliver hard motor starting
> power in a remote location. We need proven products, with a track record
> of reliability.
>
> We are considering SMA type systems that use AC coupled PV to offset fuel
> consumption of a generator, but those seem dependent on the generator to
> maintain the stability of the micro grid during hard starting loads.
> Ideally we would want to reduce the generator run time to under 200 hrs/ yr
> and reduce its size to 500 kW. We have excellent solar resources year
> round, and the possibility of limiting operations during cloudy weather to
> meet these goals.
>
> Thanks,
>
> Ray Walters
>
> Remote Solar
>
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