1 16 SINGLE-PHASE CURRENTS. [Exp. 



Admittance is the reciprocal of impedance; but conductance is 

 not the reciprocal of resistance (as with direct currents), nor is 

 susceptance the reciprocal of reactance. 



43. Pozver. It is seen that the expression for true power, 

 El cos 0, may be written in two ways: 



W = EcosOX I (resolving electromotive force); 

 or, 



WIcos6XE (resolving current). 



44. Resolving the electromotive force into components, we 

 have: True power is equal to the product of current (/) and 

 the component of electromotive force (E cos 6) which is in phase 

 with the current. 



45. Resolving the current into components, we have: True 

 power is equal to the product of the impressed electromotive 

 force (E) and the component of current (IcosO) which is in 

 phase with the electromotive force. 



46. Calculation of L and X by Wattmeter Method. React- 

 ance is by definition (40) equal to the quadrature electromotive 

 force, Ex, divided by current. 



Referring to Fig. 7, the reactance and inductance of the coil 

 R 2 L 2 are computed as follows: 



L 2 a> = X 2 = CA -=- 1, ohms ; 

 L 2 = X 2 -T- <o = X 2 -T- 2vn, henries. 



By this method, X 2 and L 2 are determined by measurements 

 of E, I and W , and are independent of the measured value of R 2 . 

 (See 47 and 49.) Note also that R 2 = OC~I=IV ^-1\ 

 and that tan = X 2 ~ R 2 . 



47. Calculation of L and X by Impedance Method. By the 

 impedance method, L 2 depends upon E, I and the measured value 

 of R 2 , and is independent of the wattmeter reading. The cal- 

 culations are made as follows: 



Impedance (ohms) Z 2 =E-^7. 



Reactance (ohms) = X 2 = \/Z 2 2 R 2 *. 



