POWER MEASUREMENT 



339 



Four-wire Three-phase System. The power will be given by 

 the sum of the readings of three wattmeters connected between 

 the leads 1, 2, 3 and the neutral point. Fig. 202 shows another 

 arrangement which also conforms to BlondePs theorem. 



FIG. 202. Connections for power measurement in a four-wire 

 three-phase circuit. 



p = 



but 013 = 014 ~\~ 043 

 "23 = 024 + 043 



so 



p = (vis + 034)1 1 + (023 + 034)12 + 034( - ii ~ it - 



1 /7 1 /r i /r 



= v l3 iidt + - t;,,^ + - 

 i Jo 1 Jo *Jo 



p = - 



(34) 



which is the sum of the readings of the three wattmeters. The 

 theorem shows that the power 1 in any four-wire combination of 

 loads may be measured by three wattmeters. 



References 



1. "Compensating Wattmeters," A. L. ELLIS, Trans. American Institute 

 of Electrical Engineers, vol. 31, 1912, p. 1579. 



2. "On the Theory of Alternating Current Wattmeters," C. V DRYSDALE, 

 The Electrician, vol. 46, 1900-1901, p. 774. " Wattmeter Correcting 

 Factors," C. V. DRYSDALE, The Electrician, vol. 55, 1905, p. 429, p. 556, 

 p. 676. "The Theory of the Dynamometer Wattmeter," C. V. DRYSDALE, 

 Journal Institution of Electrical Engineers, vol. 44, 1910, p. 255. 



3. "The Compensated Two-Circuit Electrodynamometer," Edward B. 

 ROSA, Bulletin of the Bureau of Standards, vol. 3, 1907, p. 43. "Compen- 



