Variacs

Variacs are special types of electrical transformers that only consist of one winding. This allows for the production of more compact & lighter transformers that outperform the usual two winding ones in terms of voltage regulation & efficiency. The single winding in Variacs acts as both the primary and secondary sides of the transformer and connects them electrically as well as magnetically. Therefore, with Variacs you get a lower leakage reactance, lower losses lower excitation current, and increased VA rating for a given size and mass.