Advantages of Autotransformer :-
Low losses as compared to ordinary two winding transformer of the same rating.
It has a smaller size than an ordinary transformer of the same rating.
It requires a smaller exciting current than a 2-winding transformer of the same rating.
It required less Copper than an ordinary transformer of a similar rating.
It has better voltage regulation and operates at a higher efficiency than a 2-winding transformer of the same rating.
Limitation of Autotransformer :-
An auto transformer should not be used for interconnecting high voltage and low voltage systems.
Used only in the limited places where a slight variation of the output voltage from input voltage is required.
There is a direct connection between the primary winding and the secondary. Therefore, the output is no longer directly isolated from the input.
The short-circuit current is much larger than for the two-winding transformer of the same rating.
It is not safe for stepping down a high voltage to a low voltage. in case an open circuit develops in a common part of winding then full primary voltage appears across the load, it will dangerous to both people and equipment.