Standard motor driven variable transformers have synchronous motors. They typically can have motors speeds of 60, 30, 15 and 5 second travel times from 0-100%. As the variable transformers gets larger then faster motor speeds are not available.
The motor driven models have three terminals (Raise (R), Lower (L) and Common (C). You drive the motor to raise the output voltage by applying 120VAC to the Raise and Common terminals. You lower the output voltage by applying 120VAC to the Lower and Common terminals. Limit switches are provided to prevent you from driving past the upper or lower limits. The motor circuit requires approximately 0.4 Amps when energized.
All motors are 120VAC 50/60Hz rated. Motors will run 20% slower when operated on 50 Hz.
Some customers use a three position switch (center OFF, spring return to center) to manually control the output of the Variac.
We have motor controls that will control motor driven variable transformers based on an analog voltage, analog current (4-20mADC), pot or communications signal from a computer.