136 



THE TRANSFORMER. 



After connecting to the supply, note the reading of the 

 voltmeter with the switch $, open. If the transformers arc 

 exactly similar, this will be zero. 



Close the switch, and gradually increase the load on the 

 transformer A, until the maximum load contemplated is 

 reached. For each value of the load read the voltmeter. 

 The voltage applied to the transformers should be maintained 

 constant, although a small variation will not affect the results, 

 since the voltage of both transformers will vary together. 



The readings should be tabulated and plotted in the form 

 of a curve, load current being measured horizontally and 

 voltage drop vertically. 



The curve shown in Fig. 63 shows results obtained in this 

 way on a 1 kw. transformer having a ratio of transformation 



20 

 18 

 16 

 14 



i 12 



o 



3 10 

 o 



23456789 



Amperes Load. 

 FIG. 63. VOLTAGE DROP IN TRANSFORMER. 



10 11 



12 



of 100 to 50 volts. In accordance with the formula given on 

 page 130 for the copper losses in a transformer, the drop is 

 seen to be proportional to the load. In the present case 

 the drop due to magnetic leakage was very small, but in all 

 cases the loss of voltage due to this cause would be approxi- 

 mately proportional to the load, and the curve showing the 

 voltage drop would be practically a straight line. This is 



