The operating principle of autotransformer is same as the normal transformer. But, the construction of autotransformer is different compared to the Conventional transformer.
|Parameter||Two Winding Transformer||Autotransformer|
|1||Separate Winding||Primary and secondary windings are separate.||A part of winding is common between primary and secondary.|
|2||Movable contact||No movable contact||There is a movable contact.|
|3||Type||It can operate as step up or step down.||It can work as step up as well as step down.|
|4||Copper saving||None||Copper saving takes place.|
|5||Possibility of getting a variable secondary voltage||–||Yes|
|6||Electrical isolation||Yes, there is electrical isolation between primary and secondary.||No electrical isolation between primary and secondary.|
|9||Losses in the winding||High||Low|
|12||Applications||Mains transformer, power supply, welding, isolation transformer.||Variac, starting of ac motors, dimmer stat.|
|15||Winding Material||More winding material required compared to autotransformer||Less material required|
|16||Leakage flux and resistance||High||Low|
|18||Excitation Current||Large current is needed||Small current is needed|
|19||Output Voltage||Constant (if tapping is not provided)||Variable|
Advantages of Autotransformer over Conventional Transformer
Autotransformer is better in some terms compared to the normal transformer. Here, listed some advantages of autotransformer over conventional transformer.
- The copper required for the autotransformer is very less compared to the copper required for normal two winding transformer.
- The size of Autotransformer is small. Therefore, the cost of the entire device is less compared to the normal transformer.
- It requires less copper. So, the loss in winding (copper loss) is less. So, transformer losses are less and it increase the efficiency of transformer.
- Voltage regulation of autotransformer is better than the conventional transformer.
Disadvantages of Autotransformer
Here below lists shows the disadvantages of autotransformer over conventional transformer.
- There is no electrical isolation between the primary and secondary winding. This is very dangerous for high voltage transformers.
- Due to any reason if the secondary winding is short circuited, a large amount of current will flow on the secondary side because it possesses low impedance.
- Here, on single winding divided in two parts, if the common part of winding (CB) breaks, the transformer action is lost and full primary voltage appears across the secondary.
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