THE TRANSFORMER 



303 



long as the secondary coil is floating free on the leak- 

 age flux. 



Characteristics of this Type of Transformer. Because 

 of the excessive leakage flux the primary of such a trans- 

 former has a rather low power factor; the value of the power 

 factor depends upon the separation of the coils, being 

 smaller, the greater the separation. The efficiency of this 

 type of transformer is somewhat lower than that of a con- 

 stant potential transformer. This is due to the construc- 

 tion; there is more iron in the core and more resistance 



100 200 300 400 500 600 700 

 Secondary Terminal Volts 



FIG. 195. Characteristic Curves of a Constant-current Transformer. 



in the coils than there would be for a constant potential 

 transformer of the same capacity. 



The characteristic curves of a constant current trans- 

 former are given in Fig. 195, in which are reproduced the 

 results of a laboratory test on a small constant current 

 transformer. Because of the low power factor and the 

 efficiency at light loads, it is customary to have several 

 taps on the secondary and to use that tap which makes the 

 transformer operate (on a given circuit) with its secondary 

 close to the primary, thereby producing a high power 

 factor. To prevent violent oscillation of the secondary 

 coil as the load varies, a dash-pot is employed which prevents 

 rapid motion of the secondary. From Fig. 195 it may be 



