Hey Waq,

GTAW typically is always CC (Constant Current)

Quite often with automated or mechanized GTAW the arc length (distance from tip of tungsten to work) is controlled by an adaptive feedback system that is governed by arc voltage... AVC (automatic voltage control).  As the electrode encounters changes in distance the Z-Axis will move up and down.  The machine is set to provide a specified amount of axis movement as the voltage feedback changes.

If you used CV power the amperage would vary as the arc length changed, this would probably not be favorable for any GTAW operation.

I think a good question would be, what advantage would CV be able to provide?