THE TEANSFOEMEE. 173 



M v M. 2 Source of alternating current. 



T I} T 2 Transformers to be tested. 



T s Auxiliary transformer. 



W^ Wattmeter reading power taken from line exclusive of 



power taken by primary of auxiliary trans- 

 former. 



W. 2 Wattmeter reading output of auxiliary transformer. 



V Voltmeter reading supply voltage. 



A Ammeter reading current of T r 



8 V 8 V 8 3 , Si Switches. 



R Variable resistance. 



Instructions. Connections. Connect the primary winding 

 of the auxiliary transformer to the supply mains through 

 a variable resistance and switch. The resistance should be 

 sufficient to reduce the secondary voltage of the transformer 

 to a few volts only. 



Connect one terminal of the secondary winding to one 

 supply main, and the other through the series coil of a watt- 

 meter and a switch to that winding of one of the test trans- 

 formers which is to act during the test as primary. The 

 other end of this winding of the transformer under test is to 

 be connected to the opposite supply main. 



Connect the primary* of the second test transformer 

 to the supply mains through an ammeter, and insert a switch 

 where shown in the diagram at S. 2 , so as to break the supply 

 to both test transformers independently of the auxiliary 

 transformer. 



Connect a voltmeter to measure the voltage supplied, 

 and put in two wattmeters as shown, W. 2 , to read the 

 power in the secondary winding of the auxiliary transformer, 

 and W v giving the total power supplied to the transformers 

 exclusive of that passing into the primary of the 

 auxiliary transformer. 



The secondary windings of the test transformers must 

 now be joined together through a switch. If this connection 

 is made correctly, the two primary windings will take 

 current from the supply mains, and will generate approxi- 

 mately equal voltages in their secondaries which will act in 

 opposition, each tending to send current through the other. 

 If the connections between the secondaries are the reverse, 



* Throughout the description of this experiment the winding which is 

 supplied from the mains is called the primary. 



