THE TRANSFORMER. 



219 



109. The autotransformer.* Consider the supply mains which 

 bring current from an alternator, and the service mains which de- 

 liver current to a customer, as shown in Fig. 183. There are 



Supply main & 



service 



b 



Supply znatft 



Fig. 183. 



three methods for establishing communication from ab to cd y as 

 follows : (a) By conductive connections, that is by connecting 

 wires from a to c and from b to d in Fig. 183, (ft) by transformer 

 connections, that is by connecting the primary of a transformer 

 to ab and the secondary to cd, and (c) by a combination of con- 

 ductive and transformer connections. Any transformer which is 

 connected up for this combination method is called an autotrans- 

 former. 



Supply main <* b 



Fig. 1 84. 



The action of the autotransformer may be brought out most 

 clearly .by considering a numerical example. Let the coils A 



* It is misleading to speak of the autotransformer inasmuch as a so-called autotrans- 

 former is exactly the same thing as an ordinary transformer, and it acts in the same 

 way. The name autotransformer refers to a scheme of connections. 



