What is single-phase autotransformer?
It is a single winding transformer in which a part of the winding is common to both high-voltage and low - voltage sides
Fig: Step-down autotransformer
In the figure drawn above 'abc' is a single winding in which terminal 'a' and 'c' is the high voltage terminal and 'b' and 'c' is the low voltage terminal. The winding 'b' and 'c' is known as the common winding and winding 'a' and 'b' is known as the series winding.
A step-down transformer is a transformer in which the primary voltage is higher than the secondary voltage. Here in the above diagram voltage 'VH' is applied to full winding 'abc' and the load is connected to winding 'bc'. This arrangement is called as Step down Autotransformer.
In an autotransformer, the windings are physically connected that is why a different type of terminology is used for this transformer.
TH = Tac = number of turns in full winding 'abc'
= number of turns in hv side
TL = Tbc = number of turns of the common winding 'bc'
= number of turns of the lv side
Tab = TH-TL = number of turns of the series winding 'ab'
VH = input voltage on the hv side
VL = output voltage on the lv side
IH = input current in the hv side
IL = output current in the lv side
Current in the series winding = Iab = IH
Current in the common winding 'bc' = Icb = I
Step up autotransformer
Fig: Step-up autotransformer
The step-up transformer is shown in the above figure, and we can say that the source is connected to the winding 'bc' and load is connected with the complete winding 'abc'.
Advantages of Autotransformers
Disadvantages of Autotransformers
Applications of Autotransformers