Auto transformer, what are its use in a substation?

Auto transformers are often used in substations for step up/step down where the ratio of high to low voltage is small (less than 4). These are used because they are significantly smaller than a wye/wye, which translates into cost savings.

An Auto Transformer is a transformer with only one winding wound on a laminated core. An auto transformer is similar to a two winding transformer but differ in the way the primary and secondary winding are interrelated. A part of the winding is common to both primary and secondary sides. On load condition, a part of the load current is obtained directly from the supply and the remaining part is obtained by transformer action. An Auto transformer works as a voltage regulator.

Auto transformer is kind of electrical transformer where primary and secondary shares same common single winding. So basically it’s a one winding transformer.

It is used to compensate voltage drops by boosting supply voltage in distribution systems.

Auto transformers are often used in substations for step up/step down where the ratio of high to low voltage is small (less than 4). These are used because they are significantly smaller than a wye/wye, which translates into cost savings.