POWER MEASUREMENT 



337 



It is not necessary that the neutral be accessible, for by the 

 theorem one has only to connect the potential coils at some 

 common point, as 0' in Fig. 200. 



FIG. 200. Connections for three-phase power measurements with 

 artificial neutral. 



As previously shown 



p .. - 1 r 



rri I 

 \J 'J 



but 



so 



+ 



?' ' 2 



1 C T 

 = rr\ (! 



-* Jo 



i r 71 



= - vu' 



^ Jo 



4- 

 ^ 



I FT j f*T 



m I io't"i* + - I 0M*ictt 

 ^ Jo i Jo 



sum of wattmeter readings. 



1 C T 



*Vtt + - (w 80 ' + 

 J Jo 



i r r i C T 



I v 30 'i 3 dt + - I 

 J J Jo 



i / 



ictt + 



^ Jo 



(32) 



No assumptions are made as to the resistances of the potential 

 circuits of the wattmeters. 



If the load is balanced, the readings on all three instruments 

 will be the same; this leads to the use of the F-box for the 

 measurement of balanced three-phase loads. 



22 



