Which of the following statements is/are true in regard to auto transformers?

(i) A commonly known auto transformer, variac is used in laboratories and science labs.

(ii) An auto transformer should have small transformation when used in transmission and distribution application.

(iii) An auto transformer is used to raise the voltage in an AC feeder and is known as booster.

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  1. (i), (ii) and (iii)
  2. (i) and (iii)
  3. Only (iii)
  4. Only (i)

Answer (Detailed Solution Below)

Option 1 : (i), (ii) and (iii)
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Detailed Solution

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The correct answer is option 1.

Auto Transformer

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  • An autotransformer is a transformer with only one winding wound on a laminated core. A part of the winding is common to both primary and secondary sides.
  • The power in an autotransformer flows due to both conduction and induction phenomena.
  • An autotransformer is used as a variac in the laboratory where continuous voltage over broad ranges is required. 
  • The transformation ratio of the autotransformer is given by:  \(k={V_2\over V_1}\) which lies between 0.9 to 1 which is a small value.
  • An auto transformer can be used to increase (boost) or decrease (buck) the voltage in an AC feeder, depending on the configuration. When used to raise the voltage, it is referred to as a booster.
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