168 



COMMERCIAL ELECTRICAL TESTING 



of fuse wire and applying full potential to the other 

 winding of the transformer. It is just as essential that 

 the coils of a transformer operate satisfactorily in multi- 

 ple as that two transformers so operate. 



Normal Load Heat Run 



The heat test may be conducted in several ways, all 

 of which are designed to approximate as nearly as possible 

 the operating conditions of the transformers. A run 

 with actual load might be made by using water rheostats ; 



Fig. 50 

 Connections for Heat Rut 



but as this would be very expensive, some form of motor- 

 generator method should be used. Fig. 50 shows the 

 connections for testing two transformers by the motor- 

 generator method. The secondaries of both transform- 

 ers are connected in multiple and then connected to an 

 alternator which supplies the core loss and exciting cur- 

 rent. The primaries are connected in series, opposing 

 each other; if the transformers have the same ratio, 

 the voltage from A to B will be zero. 



The secondary of an auxiliary transformer D is con- 

 nected in series with the primaries of the transformers 

 in test. Alternator E connected to the primary of 

 transformer D supplies the copper losses. The same 

 method may be used for any even number of trans- 

 formers, but it is not advisable to run more than six at 

 one time. Fig. 51 shows connections for the heat run 

 on three transformers, the primaries and secondaries 



