Quantity of conducting material required is less: The quantity of conducting material required for an autotransformer having same rating as that of an ordinary two-winding transformer is only (1 – K) times, that is, quantity of conducting material required for autotransformer = (1 – K) quantity of conducting material required for an ordinary two-winding transformer. Thus, the cost of autotransformer is less as compared to two-winding transformer of the same rating.
Quantity of magnetic material required is less: During designing, the window dimensions are decided from the consideration of insulation and conductor material. For an autotransformer, a reduction in conductor material means lower window area and, therefore, smaller core length is needed. It shows that for the same core area, the weight of autotransformer core is less. Hence, there is further saving in core material. Thus, autotransformer is more economical than a two-winding transformer when K approaches to unity.
Operate at higher efficiency: Owing to the reduction in conductor and core materials, the ohmic losses in conductor and the core loss are lowered. Consequently, an autotransformer has higher efficiency than a two-winding transformer of the same rating.
Operate at better voltage regulation: Reduction in the conductor material means lower value of ohmic resistance. A part of the winding being common, leakage flux or the leakage reactance is less. In other words, an autotransformer has lower value of leakage impedance, and hence, autotransformer has lower value of leakage impedance and has better voltage regulation than a two-winding transformer of the same output.
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