4160V Service Voltage Drop When Energizing 6000HP VFD Causes CNC Low Voltage Alarm

I’m having a problem with voltage drop on a 4160 volt service. What I have is a 4160 volt service that is feeding a 6000 hp vfd powering a tester motor. The same service supplies a 4160 to 480 volt transformer to feed other equipment in the same factory. My problem is when we energize the drive the inrush is so great that I get a low voltage alarm on my cnc equipment in the building. I’m wondering if a capacitor bank on the 480 volt side will cure my problem. 

Hi Jeff-There may be a much simpler solution.  Most VFD's have a "soft start" option.  If it's not enabled, try enabling it.  If it is enabled, try increasing the soft start ramp time.-Rick

Rick
This occurs just energizing the drive not turning the motor on. I have a vacuum breaker between the drive and the service equipment to kill the power to the drive. This breaker is set at 12,500 amps to just energize the vfd . 

My gut feeling is that something is wrong with the VFD. Having said that, you should know that my only experience with VFD's is with much smaller ones- but that high inrush just seems wrong.  Maybe some of the other guys with more experience on the really big VFD's can chime in here.Is the drive being fed with three phase power?  What's the make and model of the drive?-Rick

Rick 
The drive is 3 phase 4160 volt The drive has just been rebuilt and performance tested by Siemens it’s a Siemens drive. Siemens is also who I got the trip settings for the vacuum breaker. The drive itself is full of cells so I think those are why it has such a large inrush. The reason I say that is, when the drive hasn’t been energized for a few days it has a much larger inrush than  when we’ve been running it often.  

That's very curious.  From what I understand, the single phase input VFD's often have large electrolytic filter capacitors that can cause a significant inrush, but the 3 phase input VFD's have little, if any capacitive filtering. I think Siemens might be your best bet for answers to the problem.
Back to the original question- I don't think a capacitor bank on the 4160 volt 3-phase supply will help resolve the problem.

-Rick

UPDATE- I just found a Siemens document about VFD's , and on page 8 it says: "At first switch on the DC link capacitors are discharged, and the inrush
current must be limited, usually using a resistor which is bypassed by a
relay after a few seconds."
it is unclear whether this requirement is handled within the VFD or whether it must be an external add-on.  Probably need to ask Siemens about this.-Rick

Rick 
Siemens has been onsite probably 10 times.  They say the drive is functioning normally. I’m wondering if a capacitor bank would work on the 480 volt side to keep the voltage up when we energize the drive.  

Hi Jeff-I don't see how a capacitor bank on the AC side will help.  If everything was fed with DC, then yes, but on AC the capacitor bank will only help with VERY narrow current spikes- less than one cycle.  What are your thoughts about Siemens' comment concerning current limiting resistors? 
-Rick