VFD and short circuit

[bozzah]

I'd like to know how does a VFD affect a short circuit level; two 7500hp motors (fed from 4.16kV, s/gear) are controled by VFDs. In case of the 3ph bolted fault at the gear, motors act as generators adding fault current at the bus. Having VFDs in series with motors, is there any change in fault generated at the bus (assumed motor run at full load)?

 

[davidbeach]

Considering that the motor is no longer connected to the bus, but rather is connected to the VFD you will find that it produces next to no fault current. That may be a bit different if you have a four quadrant regenerative drive, but even then the fault current will be not much more that full load current; and not for very long.