Construction of single phase auto transformer: (i) It has only one winding wound on a laminated circular magnetic core. (ii) The core is made of silicon steel stampings. (iii) The two terminals of the winging are connected to the supply. (iv) A variable point on the winding is connected to a carbon brush and brush can be moved by a circular handle.
Working of single phase auto transformer:
1) The transformer which works on the principle of self-induction and gives variable output voltage is called an auto transformer. 2) The primary winding is connected to the supply and it has N1 number of turns as shown in above diagrams. 3) By moving the handle we can select N2 number of turns on the secondary. Thus the same winding can function as primary as well as secondary. 4) Hence, from the auto-transformer we can get a variable voltage by varying N2 by moving the brush with the help of handle. 5) The same transformer can be used as step-up or step down auto-transformer