BIPOLAR DIAGRAM 



151 



the synchronous reactance, and the corresponding impedance 

 Z=\/r 2 -\-X 2 is called the synchronous impedance. The use of 

 these quantities reduces the synchronous motor or alternator to a 

 very simple basis, although at the expense of accuracy. 



It is then possible to subdivide the impressed E.M.F. E\ into 

 three components; E F) necessary to balance the counter E.M.F. Ep 

 which is due to the excitation'/' 1 considered as acting alone; Ir con- 

 sumed by resistance; and IX consumed by the synchronous react- 

 ance X: or, the synchronous impedance E.M.F, IZ may be looked 



FIG. 73. 



upon as the resultant of the impressed E.M.F. E\ and the counter 

 E.M.F. Ep. This is shown more clearly in the simplified E.M.F 

 diagram of Fig. 74, where 2 corresponds to the E F ' of Fig. 73, and 

 E=IZ. The current / will then lag behind the resultant E.M.F. E 



X 

 by an angle whose tangent is . 



The transformation from Fig. 72 to Fig. 73 consists in substituting 

 for the armature M.M.F. A, an E.M.F. E A ', which would be induced 

 in the armature by cutting the flux $ A) which in turn would be 

 produced by the M.M.F. A if acting in a magnetic circuit of the same 

 reluctance as that in which R produces <i>. 



