THE TRANSFORMER. 



131 



Instructions. Connect the primary of the transformer 

 to a source of alternating current. 



Connect the secondary to a variable non-inductive 

 resistance in series with an ammeter and a switch. 



Connect voltmeters to the terminals of the primary and 

 secondary windings. 



Beginning with open secondary circuit, read primary 

 and secondary voltage. Then close the switch, and repeat 

 the readings for increasing values of secondary current. 

 The primary voltage and frequency should be maintained 

 constant throughout the experiment. It is most important 

 to remember that it is no use to determine the drop in the 

 transformer windings until they have attained their normal 

 working temperature. It will therefore be necessary to run 

 a large transformer for several hours before taking readings 

 in order to make them correspond with working conditions. 

 Small transformers will arrive at steady temperatures much 

 sooner. It is usually convenient to make the regulation 

 test during, or after, the trial run in the case of a new trains - 

 former. 



Tabulate the results under headings, as follows : 



REGULATION TEST OF A TRANSFORMER. 



Transformer No Type 



Output kw cycles per second. 



Ratio of transformation to . . . . volts. 



. , Number of primary windings 



~ Number of secondary windings 

 F 02 = no-load secondary voltage. 



No-load primary voltage. 

 No-load secondary voltage- 



At no-load the ratio of primary to secondary volts will be 

 practically equal to the ratio of the number of the windings. 



If no loss occurred in the transformer this would, there- 

 fore, be the ratio of transformation at all loads. The difference 

 between this theoretical value of the secondary voltage and 

 the actual value is termed the " drop " of the transformer. 



