172 



THE TRANSFORMER. 



to the other. The secondary voltages will consequently 

 be unequal also under these conditions, and a current will 

 be produced, the amount depending on the extent of the 

 out-of-balance voltage. By varying the voltage of the 

 auxiliary transformer any required current may be obtained 

 in the secondary windings. A current in the secondary 

 winding must, however, necessarily correspond to a current 

 in the primary, and consequently both transformers will 

 carry a primary current, but in opposite directions relative 

 to the supply circuit. If the auxiliary transformer assists 

 the transformer to which it is connected, the secondary of 

 this transformer will overcome the secondary of the other, 

 and its primary will take current from the mains. The 

 current in the secondary of the other transformer will be 

 the reverse of that which its primary tends to send, and 

 will consequently produce a reverse current in the primary, 

 and this transformer will supply current to the mains. If 

 the auxiliary transformer opposes the voltage of the first 

 transformer, exactly the reverse conditions will arise. In 

 either case the power supplied to the mains is nearly the 

 equivalent of the power taken from them, the difference 

 depending on the efficiency of the transformers. 



EXPERIMENT XXXII. DETERMINATION OF EFFICIENCY 

 OF A PAIR OF TRANSFORMERS BY SUMPNER'S METHOD. 



DIAGRAM OF CONNECTIONS. 



.V 



FIG. 81. 



