THE TRANSFORMER. 



157 



inductance had been added in the primary circuit. The effect 

 of a lagging secondary current is, consequently, to produce a 

 lagging primary current, and to reduce the ratio of secondary 

 to primary voltage. An inductive secondary load produces, 

 therefore, similar results to the magnetic leakage just discussed. 

 Efficiency Tests of a Transformer, The most direct 

 method of measuring the efficiency of a transformer is to 

 measure the power supplied by one wattmeter, and the power 

 given out by a second wattmeter. The ratio of the two 

 quantities measured, then gives the efficiency, since 



-nee output 



Efficiency = , i 



input 



If the load on the secondary circuit is non-inductive, 

 readings on a voltmeter and ammeter will be sufficient to give 

 the output, since there will be no phase difference in the 

 circuit, and consequently watts output = volts x amperes. 



The properties of the transformer are in general more 

 easily studied when the load is non-inductive, and conse- 

 quently tests of efficiency are nearly always made on non- 

 inductive loads. Transformers are not generally tested on 

 inductive loads except to determine whether they are suitable 

 for working under certain given conditions, or in accordance 

 with a specification. 



EXPERIMENT XXIX. EFFICIENCY TEST OF A TRANS- 

 FORMER ON NON-INDUCTIVE LOAD. 



DIAGRAM OF CONNECTIONS. 



S 2 



FIG. 72. 



M,,l 

 I, II 

 R 



V, 

 V, 



Source of alternating current. 

 Primary and secondary windings of transformer. 

 Variable non-inductive resistance for altering load . 

 Voltmeter for reading primary voltage. 

 Voltmeter for reading secondary voltage. 

 Ammeter for reading primary current. 



