158 



THE TRANSFORMER. 



A. 2 Ammeter for reading secondary current. 



W Wattmeter for reading primary input. 



C Voltmeter Switch or plug. 



S Switch for breaking secondary circuit. 



Instructions. Connect the primary of the transformer 

 to a source of current, having suitable voltage and frequency, 

 in series with an ammeter.* Connect a wattmeter in the 

 primary circuit to read the watts supplied to the winding and 

 join a voltmeter to the primary terminals. 



Connect the secondary winding to a variable non-inductive 

 load resistance in series with an ammeter and switch. Join a 

 voltmeter to the secondary terminals of the transformer. 



It is well to insert a voltmeter switch, as shown at C, 

 in the circuit of the voltmeter and volt coil of the watt- 

 meter, so that these instruments are only in the circuit 

 when their readings are being taken. Errors due to the 

 current taken by these instruments may not be negligible 

 at small loads. 



Maintain the applied voltage constant during the measure- 

 ment, and take readings of primary watts and primary and 

 secondary current and voltage, first on open circuit and then 

 with gradually increased loads. 



Tabulate the readings as in the following table : 



LOAD TEST OF A TRANSFORMER. 



Transformer No Type 



Output kw cycles per second. 



Transformation . volts to volts. 



* The primary current need not necessarily be measured if the efficiency 

 only is required. It is, however, desirable to put an ammeter in the primary 

 circuit to enable the no-load current and the power factor of the primary 

 circuit to be observed. Both these quantities are of great importance. 



