VFD Voltage
VFD Voltage
(OP)
We have a design with 12 motors each 3.3 kV (power ratings from 300 Kw to 1000 Kw) 9 motors have VSD drives the other 3 have soft start.
Incoming power supply is 11 kV. My question is why do we not transform the incoming supply to 3.3 kV instead of having one 3.3 kV transformer on each drive (12 No 11/3.3 kV transformers in total) ?
Incoming power supply is 11 kV. My question is why do we not transform the incoming supply to 3.3 kV instead of having one 3.3 kV transformer on each drive (12 No 11/3.3 kV transformers in total) ?





RE: VFD Voltage
I recall that old drives used to all require transformers.
Keith Cress
kcress - http://www.flaminsystems.com
RE: VFD Voltage
RE: VFD Voltage
RE: VFD Voltage
The lower fault available currents may have allowed the selection of less expensive 3.3 kV equipment and less stringent Arc Flash requirements.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: VFD Voltage
1) You need to step down the voltage.
2) You need to mitigate harmonics created by the VFDs (assuming these are VSI drives).
3) You need some galvanic isolation between drives for Common Mode Noise attenuation.
4) You need to limit the available fault current feeding each drive.
One large transformer ahead of all of them solves #1 only.
You don't need an individual transformer ahead of each soft starter, but it could be that they may want to some day upgrade those to VFDs as well.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington