218 



ELEMENTS OF ELECTRICAL ENGINEERING. 



The primary coils of several transformers may be connected in 

 series with each other as shown in Fig. 182. This arrangement, 

 which is called the series connection of transformers, is seldom 

 used. 



Transformers with divided coils. Alternators in moderately 

 small lighting plants give usually 1,100 or 2,200 volts electromo- 

 tive force, and the standard voltages for incandescent lamps are 

 1 1 o volts or 220 volts. Small transformers for lighting plants are 

 therefore usually made with two-part primary coils and two-part 



- ^ j , ^X 



IQQQQQQJ IQQQQQOJ UMoJ 



Fig. 182. 



secondary coils, so that the two parts of the primary may be con- 

 nected in series with each other for 2,200 volts or in parallel 

 with each other for 1,100 volts, and so that the two parts of the 

 secondary may be connected in series with each other for 220, 

 volts or in parallel with each other for no volts. 



In connecting the two parts of a transformer coil in parallel 

 with each other the utmost care must be taken to connect the 

 coils so that one coil does not act as a short-circuit for the other, 

 and in connecting the two parts of the primary coil of a trans- 

 former in series with each other the utmost care must be taken 

 to be sure that the two parts work together in opposing the 

 primary impressed voltage. Failure in either case to make the 

 proper connections may lead to serious damage to the transformer 

 when it is connected to the mains. 



