222 



ALTERNATING CURRENTS 



addition to insulating the instruments from high-voltage, they 

 step down the current in a known ratio. This enables a lower- 

 range ammeter to be used than would ordinarily be required if 

 the instrument were connected directly into the primary line. 



13,200 



Volts 



Load 



FIG. 213. Connections for a series or current transformer on a 13,200-volt 



circuit. 



The current or series transformer has a primary, usually of 

 few turns, wound on a core and connected in series with the line, 

 Fig. 213. When the primary has a large current rating, it may 

 consist of a straight conductor passing through the center of a 



Prlmnryx 



Secondary Flux 



FIG. 214. Construction of one type of current transformer. 



hollow core, as shown in Fig. 214. The secondary, consisting 

 of several turns, is wound around the laminated core. The ratio 

 of current transformation is approximately the inverse ratio of 

 turns. For example, if the primary has two turns and the sec- 



