TRANSFORMERS 



181 



as to the proper method for measuring core loss. If the 

 neutral connection is broken (as is sometimes necessary 

 for the heat run), the secondaries may be connected 

 in delta and three-phase voltage applied. This voltage 

 is the same as the diametrical voltage, or that of each 

 phase. If the neutral can not be broken, the secondaries 

 may be connected in Y, the neutral connection forming 

 the Y point. In this case the voltage corresponding to 



V3 

 the normal voltage of the transformer will be times 



Three -pho se Voltage 



vwws 



Fig. 61 

 Connections for Parallel Run, Three-Phase 



the diametrical voltage. It should be remembered that 

 the middle set of coils should be connected so as to be 

 reversed with respect to the other two, in order to obtain 

 the proper magnetic flux in all parts of the core. 



Hold the voltage constant and take readings as in 

 impedance test. There will be a slight unbalancing of the 

 magnetizing currents due to the unequal magnetic reluc- 

 tances in the different parts of the core. For this reason 

 the alternator for core loss tests must be operated at 

 normal voltage so as to balance the three-phase voltage 

 as nearly as possible. 



Parallel Run 



The parallel run checks ratio and polarity on a three- 

 phase transformer in the same way that it does on a 

 single-phase transformer. 



