190 THE TRANSFORM] '.I!. 



C,. Imaginary secondary current equivalent to 



iron losses. 



E., Secondary induced voltage. 



E., r Secondary terminal voltage. 



C m Magnetising current. 



F Flux in core. 



Tracing of Curves of Primary and Secondary Voltage. The 

 method of determining experimentally the wave form of the 

 voltage of an alternator (see page 85) may be extended to 

 the determination of the wave form of primary and secondary 

 voltage of an alternator, either on open circuit, or when loaded. 



The rotating contact must be driven synchronously by 

 the generator supplying the current ; the portion of the 

 circuit which is connected through the contact to the volt- 

 meter can be chosen at will. Thus the primary terminals 

 of a transformer supplied by the alternator may be con- 

 nected through the rotating contact to the voltmeter, and 

 a curve of primary voltage obtained by moving the contact 

 brush into a series of positions. Simultaneous readings 

 may be taken on the secondary winding by throwing over the 

 voltmeter connections to the secondary terminals for each 

 position of the contact. The two curves of primary and 

 secondary volts may then be traced on the same sheet of 

 squared paper. Similar curves for a transformer loaded 

 non-inductively and inductively should be obtained by the 

 student. 



General Note to Chapter VI. In all the discussion given 

 in this chapter, the wave form of current and voltage has been 

 assumed to be sinusoidal. In the case of transformer work, 

 this is never accurately true, on account of the variation 

 in permeability of the core corresponding to the varying 

 magnetising currents. It has been thought to be advisable, 

 in order to obtain simplicity, not to go into the question 

 of distortion of wave forms, but to refer the student 

 who wishes to study the question more completely to the 

 more mathematical treatises on the subject. The results 

 obtained as described are in most cases sufficiently accurate 

 for commercial purposes. 



