TRANSFORMERS 



169 



of which are connected in delta. Across one corner of 

 the delta, impedance voltage is impressed for the three 

 transformers connected in series. The current circulates 

 within the delta and is entirely independent of the sec- 

 ondary voltage. 



The two methods outlined above require only sufficient 

 power to supply the losses. 



Alternator 

 Supplying Copper 

 Losses 



To Tnree-phase Alternator 

 Supp/ytnc/ Core Loss 



Pr imary 



Fig. 51 

 Connections for Heat Run 



In arranging for the heat run, see that the alternators 

 and transformers are of sufficient capacity to carry the 

 load ; the current necessary to supply the iron losses being 

 equal to the sum of the exciting currents of the trans- 

 formers. If the transformers have several secondary 

 coils, connect them in series so that when the heat run 

 is completed no time will be lost in making connections 

 for measuring hot resistance. The alternator supplying 

 the core loss should operate at normal excitation; the 

 voltage required to supply the load current being equal 

 to the impedance voltages of the transformers. If there 

 is more than one primary, arrange to run them in series 

 if possible. If the transformer is to have a 50 per cent 

 overload test, add 5 per cent to the voltage already 

 obtained. 



