Variable Auto Transformers are made to deliver variable AC source from the constant AC foundation. They are most commonly used in schools as well as colleges. These transformers offer a controlled voltage supply. The functional advantages of the transformers are many. These are finer than the conventional double wound convertors. Variable Auto Transformers are usually more efficient. They have less copper in their construction and are known well for their cost-efficiency. Also known as variac, these are suited to adjust the AC voltage for electronic lamps and devices.