Explain the working of auto-transformer and state any two advantages of it.
1 Answer
Answer :
Working of auto transformer :-It is a transformer with one winding only, part of this being common to both primary and secondary. In this transformer the primary and secondary are not electrically isolated from each other as in case with a two winding transformer. But the theory and operation are similar to that of two winding transformer. In fig a below, AC acts as the primary winding and portion BC of the same winding behaves as secondary winding and load is connected across BC. The output voltage across load is less than the input voltage connected to AC .The auto transformer behaves like a step down transformer.
In fig b below, AC acts as the secondary winding and load is connected across AC and portion BC of the same winding behaves as primary winding. The output voltage across the load will be greater than the input voltage across BC. So the auto transformer behaves like a step up transformer
Advantages :- 1. Copper required in an auto transformer is less than that of conventional two winding transformer hence it is cheaper. 2. The resistance and leakage reactance of an auto transformer is less than the corresponding two winding transformer , so its regulation is better. 3. I 2 R losses of an auto transformer are less, so the efficiency of auto transformer is higher than that of two winding transformer.