6-B] MEASUREMENT OF POWER. 239 



connected to different points on this resistance. The load re- 

 sistance itself can be thus utilized. 



The experiment might be extended to using 3 wattmeters on 

 a 3-wire system, 4 wattmeters on a 4-wire system, etc., but this 

 seems hardly necessary. The method of n wattmeters, n I 

 wattmeters and two wattmeters may, in this way, be experi- 

 mentally verified. 



50. Two-phase Power Factor. From one phase, 'A, of a 

 2-phase supply draw a single-phase load. Take measurements 

 with a voltmeter, ammeter and wattmeter and determine the 

 power factor by the " cosine method," 14. 



Transfer the voltmeter and potential coil of the wattmeter 

 to the other phase, B, and determine the power factor by the 

 "sine method," 13, and by the "tangent method," 12. 



51. Three-phase Power and Power Factor. With a 3-phase 

 balanced load supplied from a 3-phase circuit, take two readings 

 of a wattmeter connected as in Fig. 7. Determine the total 

 power ; calculate the power factor by the tangent formula, 28, 

 and by the ratio of wattmeter reading, Fig. 3. 



52. Transfer the potential coil of the wattmeter to the third 

 phase, so as to read the "quadrature" volt-amperes; take the 

 necessary readings of the wattmeter, voltmeter and ammeter, and 

 determine power factor by the " sine method," 43. 



APPENDIX I. 



MISCELLANEOUS NOTES. 



53. General Proof. In any system, with any number of con- 

 ductors a, b, c, etc., let the instantaneous values of the currents in 

 these conductors be * , t* 6 , i c , etc. Designate by e a , e b , e c , etc., the 

 instantaneous values of the potentials of the several conductors. The 

 currents and electromotive forces may vary in any manner what- 

 soever. There is no limitation as to the arrangement or method of 

 connection of the generator and receiver circuits. 



