Advantages of an Autotransformer :-
 

1) Copper required is less.

2) The efficiency is higher as compared to two winding transformer.

3) The size and cost is less.

4) The resistance and leakage reactance is less.

5) Copper losses is less.

6) Due to less resistance and leakage reactance voltage regulations is superior.

7) A smooth and continuous variation of voltage is possible.

8) Volt-Amp rating is more as compared to two winding transformer.

Disadvantages of an Autotransformer :- 



1) Low impedance hence high short-circuit current causes short-circuit on secondary side.

2) If a section of winding common to primary and secondary is open full primary voltage appears across the secondary winding and creates danger of accident.

3) No electrical separation in primary and secondary which is risky in case of high voltage level.

4) Economical only when volt ratio is less than 2.

Application of an Autotransformer :- 
1) For safety starting a machine induction, Sinchronize motor.

2) To give a small boost to a distribution cable to compensate a volta drop.
 i.e. It is used as a booster.

3) As a furnace transformer to supply power at the require voltage.

4) It can be used to vary the voltage to load smoothly from "0" to rated Voltage.
i.e. It is used as a dimmerstat.

5) For interconnecting system which are operating roughly as the same voltage level.