150 



THE TRANSFORMER. 



Connect a wattmeter to this circuit so as to read the power 

 supplied. Connect a voltmeter to the terminals of the same 

 winding. Supply to the transformer current of different 

 frequencies, commencing with the lowest periodicity, for 

 which satisfactory readings can be taken, taking care that 

 the induction produced in the transformer remains constant. 

 This can be most simply insured by adjusting the voltage 

 in each case to the value of the first reading, increased in the 



V 

 proportion of the frequency. Thus the quantity should 



71^ 



be kept constant where n = frequency and V = voltage. 



Take readings on the wattmeter and ammeter after 

 adjusting the voltage to the value required to correspond to 

 each value of the frequency. The readings should be 

 entered in tabular form, and two curves plotted with 

 frequency measured horizontally, and wattmeter readings 

 and current vertically. A tangent drawn to the curve of 

 watts at its lowest point and passing through zero divides 

 the losses according to their causes as already explained. 



Results should be entered as in the following example. 



SEPARATION OF IRON LOSSES IN A TRANSFORMER. 



Transformer No Type 



Output .... kw cycles per second. 



Ratio o f transformation . . volts to ... volts. 



The curve shown in Fig. 68 gives the results obtained from an 

 experiment carried out not on a transformer, but on a choking 

 coil. The coil was chosen in preference to a transformer, 

 as it was found that owing to the larger currents taken, and 

 the less perfect lamination of the magnetic circuit, much 

 more marked variations in the power could be obtained 

 than with the transformers which were available. When 



