[RE-wrenches] Large Off Grid Inverter?

[bzp]

Try a three phase soft starter. Programmable start ramp time with relay 
bypass. Not as expensive as a full blown VFD.

Frank BZP.



On 4/26/2018 9:17 AM, Dave Angelini Offgrid Solar wrote:
> Agree with Daryl here at the end. You have to solve the motor surge with
> variable frequency drive and go 3 phase. If there is a reasonable cost to
> use the grid I would not even bother with quoting an off the grid
> solution. It is what the grid is best at and batteries are the wrong way
> for this.
>
> Dave Angelini Offgrid Solar
> "we go where powerlines don't"
> http://members.sti.net/offgridsolar/
> e-mail  offgridsolar at sti.net
> text 209 813 0060
>
>> 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 <ray at solarray.com> 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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