POLYPHASE SYSTEMS 



87 



Th<> power-factor of the delta-system is the same as that fora 

 Y-eyBtem, 



P - F - = = cos - (33) 



where /' is tho total power of the system, and E and / are the 

 line voltaic and line current respectively. 



The denominator, \/3 El, equation (33), gives the volt-amperes 

 of t he three-phase system. The kilovolt-amperes of a three-phase 

 system are given by 



METHODS OF MEASURING POWER IN THREE-PHASE SYSTEM 



47. Three-wattmeter Method. Let (1), (2) and (3), Fig. 86 

 (a), bo the three coils of either a Y-connected alternator or of a 



H6. The 3- wattmeter method of measuring 3-phuse power. 



Y-ennnerted load. If the neutral of the Y is accessible, it is 

 possible to measure the power of each phase by connecting the 

 cunvnt-coil of n wattmeter in wriM with the phase and by con- 

 nertinLr tl, ( . wattmeter |)otential-coil across the phase, as shown 

 in \'\. sr. (a), 'I'heivfnn- ,11',, ]i*o and H', measure the pnwer 

 in loads 1, 2, and 3 respectively, regardless of power-factor, 



6 of balanre, etc. 

 The total power 



p = Wi + W* + Wt 

 If the loads are balanced, 



w l = w , - Wi 



