A. It is type of transformer with only one winding a portion of which is shared by both primary and secondary. Advantages: It is used where transformation ratio differs little from unity. As it contains only one winding, it uses less copper and hence cheaper. Its efficiency is more when compared with the conventional one. Its size is relatively very smaller. Voltage regulation of auto transformer is much better. Lower cost Low requirements of excitation current. Less copper is used in its design and construction In conventional transformer the voltage step up or step down value is fixed while in auto transformer, we can vary the output voltage as per out requirements and can smoothly increase or decrease its value as per our requirement.