THE TRANSFOEMER. 



147 



The curves shown in Fig. 67 were obtained in this manner, 

 and show that both current and watts increase with a decrease 

 of periodicity. This is owing to the fact that the induction 

 in the transformer core must be increased at low periodicity 

 for the terminal voltage to remain constant. The magnetis- 

 ing current increases with a decrease of periodicity in 

 consequence of this. The current spent in overcoming eddy- 

 current losses in the core remains practically constant in 

 amount, since these currents are proportional to the square 

 of the periodicity and the square of the induction, and these 

 two quantities vary in an inverse ratio in the experiment. 

 The hysteresis losses, however, decrease with an increase of 

 periodicity, since they are proportional to the product of 

 periodicity and of the induction raised to the power 1-6. 

 Consequently an increase of induction will more than counter- 

 balance a proportionate decrease in periodicity. The fall 

 of power at increased periodicities is, therefore, chiefly owing 

 to a decrease in the hysteresis losses. 



Perhaps the most interesting point illustrated by the 

 curves is the decrease in both current and power brought 

 about by the higher frequency. It is easy to see from these 

 results that an increase of frequency would enable a smaller 

 core, and consequently a less expensive transformer, to 

 serve a given purpose. 



10 



43 



50 



20 30 



Periods per second. 



FIG. 67. NO-LOAD CURRKNT AND WATTS IN TRANSFORMER AT VARIOUS 



FREQUENCIES AND CONSTANT VOLTAGK. 



Upper Curve - Current. 



Lower Curve - Watts. 



