'<S-A] GENERAL STUDY. 203 



shrink to the delivered voltages, OA' and OB' ; the drop due to 

 resistance in lines A and B is in phase with the currents /A and 

 7 B . There is the same phase difference (90 ) between the deliv- 

 ered voltages as between the supply voltages. 



For the second case (Fig. 9), the line drop in the common 

 conductor is in phase with /, and it is seen that, on account of 

 this drop, the phase angle between the delivered voltages is 

 greater than between the supply voltages. This, also, is true in 

 Fig. 10. This lack of symmetry in delivered voltages is one dis- 

 advantage of the 3-wire system ; see 3. 



15. These diagrams illustrate the topographic or mesh 

 method for representing electromotive forces. The direction 

 assigned to any line depends upon the sense in which it is taken. 

 Resistance drop consumed by resistance is in phase with cur- 

 rent; resistance drop produced by a resistance is opposite to the 

 current, as discussed in Exp. 4-A. It is taken in this latter sense 

 in applying the mesh principle, Law (i) of Appendix I. that 

 the electromotive forces around any mesh have a vector sum of 

 zero and can be represented as a closed polygon. Thus, in 

 Fig. 10, proceeding around the mesh OAA'O', we have the fol- 

 lowing electromotive forces: OA produced by the generator; 

 A A' produced by resistance in line A and opposite to /A; A'O f 

 the counter electromotive force produced by the load (the elec- 

 tromotive force delivered to the load being O'A') ; O'O pro- 

 duced by resistance in the common line O and opposite to 7. 

 The line drop for a single-phase circuit can be similarly repre- 

 sented. 



With inductance in the lines, besides the resistance drop just 

 discussed, there is a reactance drop at right angles to the cur- 

 rent ; this reactance drop is 90 ahead of the current when con- 

 sidered as consumed by reactance, and 90 behind the current 

 when considered as produced by reactance. (See i8a and Fig. 

 2, Exp. 4-A, and Figs. 3, 4 and 5, Exp. 3-6.) 



16. The line drop diagram, Fig. 10, is true for any 3-wire 



