142 



THE TRANSFORMER. 



Instructions. Connect one coil of the transformer to a 

 supply of alternating current. It will generally be found 

 advisable to choose the low-tension winding or a part of this 

 winding for the purpose, in order to get a magnetising current 

 sufficiently large to be conveniently read. Connect a low- 

 reading ammeter in series with the supply, and a wattmeter 

 to read the power supplied. Connect a voltmeter to the 

 same winding. 



Keeping the periodicity of the current constant, vary 

 the voltage at the terminals of the transformer connected 

 to the supply, from a low value upwards. This may be done, 

 either by varying the excitation of the alternator supplying 

 the transformer, or by gradually cutting out a resistance 

 inserted in series with the transformer winding. For each 

 value of the voltage take readings of the voltmeter, ammeter, 

 and wattmeter. Enter the results in tabular form as shown, 

 below. The coil supplied with current is here called the 

 " primary," although it may be intended to be used as 

 secondary under normal conditions. 



If the secondary winding is used in the experiment, the 

 value of the no-load current which would be supplied to the 

 primary when connected to the supply may be calculated 

 by dividing by the ratio of primary to secondary windings. 



DETERMINATION OF TRANSFORMER MAGNETISING 

 CURRENT AT VARIOUS VOLTAGES. 



Transformer No Type 



Output .... kw periods per second. 



Ratio of Transformation . . to . . volts. 



From the results of this experiment a curve should be 

 plotted, comparing the primary voltage with the magnetising 

 current. Usually the volts lost in the winding at no-load 



