Variable Autotransformer

Variacs or variable auto transformer is a Continuously variable voltage transformer, having a single layer winding on a toroidal core of high grade Steel. In an autotransformer portions of the same winding act as both the primary and secondary winding. the winding has at least three taps where electrical connections are made. One end of the winding is usually connected in common to both the voltage source and the electrical load. The other end of the source and load are connected to taps along the winding. Different taps on the winding correspond to different voltages, measured from the common end.