Vertical Roller Contact Variacs

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) type connections.
This finds application mainly in Plating rectifiers, high voltage Testing Equipments, high power automatic voltage regulation (Servo Stabilisers)

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).