GENERAL STUDY. 



205 



and for clearness may be designated by the subscript D thus, 

 ED. When nothing further is specified than the voltage E of 

 a 3-phase line or machine, it is this delta or line voltage that 

 is meant. 



Measure* the star voltage E$ (called also voltage per phase 

 or phase voltage, 30) from each line to the junction 0, Fig. n. 

 Also measure the star current /s for each phase. The line cur- 

 rent is always the star current, as is evident for this case. 



Compare the measured values of ED and Es with the expres- 

 sion (which should be proved) 



ED= V3 s. 



20. Compute the power for each resistance. This is obvi- 

 ously, as in a single-phase circuit, equal to the product of volts X 

 amperes (for a non-inductive load), 

 i. e., the product of star voltage and 

 star current (Es/s) for each phase. For 

 an inductive load in which the current 

 lags by an angle 0, as in Fig. 12, the 

 power for each star circuit is E$ /s cos 0. 

 When ES, /s and 6 are the same for each 

 phase, we can multiply the power for 

 each phase by 3 to obtain the total 

 power ; thus, 



.ft- 



Total power = 3^5/5 cos 0. 



FIG. 12. Currents and 

 voltages in a star-con- 

 nected 3-phase circuit, 

 radial method of represen- 

 tation. 



But 



hence 



s = D -f- V3; 



Total power = \/^E D /s cos 



* (i9a). If the neutral point of the supply is available, measure the 

 voltage between it and O, and test with a telephone as described in Appen- 

 dix II., 44. This can be done either in connection with the present test 

 or later in connection with Appendix II. 



