This Variac construction looks like a conventional 3 ph transformer as can be seen in the picture. The
spatiality of this lies in winding Cu strip of appropriate cross section edgewise. This reduces the length of the column to 1/4 as compared to winding widthwise thus making it compact. This column is then polished & roller carbons are made to make contact with winding for current collection. Due to circular column construction, a Double Carbon assembly can be provided giving two outputs 1800 out of phase (or as it is known + and - type).
Then this type of variac can give +/- type output with carbon assembly moving in opposite directions (up/down). For large current ratings these columns can be
paralleled. Also being in three phase construction it can be used for higher Currents in delta (p)
This finds application mainly in Plating rectifiers, high voltage Testing Equipments, high power automatic voltage
regulation (Servo Stabilisers)