152 



THE TRANSFORMEE. 



EXPERIMENT XXVIII. DETERMINATION OF COPPER 

 LOSSES IN A TRANSFORMER. 



DIAGRAM OF CONNECTIONS. 



fj, M 2 



I, II 



W 



A 



S 



Source of alternating current. 



Transformer windings. 



Wattmeter. 



Ammeter. 



Switch. . 



Instructions. Connect either primary or secondary wind- 

 ing of the transformer to the source of alternating current 

 through a switch, inserting a wattmeter to measure the power 

 supplied. Connect an ammeter directly to the terminals of 

 the other winding. 



Arrangements must be made for varying the voltage 

 supplied to the transformer, which throughout the experiment 

 will receive only a few volts. The variation may be accom- 

 plished either by varying the excitation of the alternator 

 supplying the current, or by a resistance in series with the 

 transformer winding. 



Commencing with only a volt or two, gradually increase 

 the applied voltage until the current read on the ammeter 

 is the full-load current of the winding to which the ammeter 

 is connected. For each value of the voltage applied take 

 readings on the wattmeter and ammeter. 



On account of the very low induction used, the losses due 

 to magnetisation of the iron may usually be neglected, and the 

 wattmeter reading may then be taken to be equal to the power 

 lost in the resistance of the windings. If it is found that the 

 wattmeter gives a reading when the secondary circuit 

 is open, then this reading should in each case be subtracted 

 from the reading taken with the circuit closed for the same 

 applied voltage. The power supplied to the transformer on 

 open circuit has already been discussed and shown to be 

 due to the iron losses. 



