THE TRANSFORMER. 221 



to the receiving circuit in the first case, or 9 kilowatts in the 

 second case. This illustrates the most important feature of the 

 autotransformer when the supply voltage is to be only slightly 

 raised or lowered, namely, that a small transformer suffices for 

 the delivery of a large amount of power, and of course the losses 

 of power are less than would be involved in a large transformer 

 used in the ordinary way. 



The action of the autotransformer in altering the supply volt- 

 age is most clearly represented as shown in Figs. 185 and 186;* 



Supply main 



Fig. 186. 



Fig. 185 represents auto-step-up transformation, and Fig. 186 

 represents auto-step-down transformation. In each of these 

 figures the two coils A and B are related to each other as 

 parts of one continuous winding, and the voltage of the whole 

 winding (A and B together) is to the voltage of any given 

 part of it as the whole number of turns is to the number of turns 

 in the given part. 



110. The arrangement of transf orjie^ } &L polyphase systems. 



( Without changing-^the number ^T/ff^^) Step-up and step- 

 down transformation*" in polyphaskpsy stems is &<66napfo^ied T in 

 general, by using an independent-transformer for each phase, that 



1 $ra*irfo 



lo sulsv iBoharru/n noraraoo 



transformer as an autotransformer. 



