272 



ELECTRICAL ENGINEERING 



of the impressed e.m.f. and inversely proportional to the number 

 of pairs of poles; it is 



n = =^-r.p.s (260) 



P P 



This is the speed at which the motor operates and it is constant 

 independent of the impressed e.m.f. of the field excitation and of 

 the load. 



Direction of Revolving Field and Torque 



Current in Phase 1 



<D\ 







Two-pole, two-phase synchronous motor. 



163. Vector Diagrams. If an alternating e.m.f. E is im- 

 pressed on the terminals of a synchronous motor of resistance r 

 and synchronous reactance XQ and a current / flows in the armature, 

 the phase relation of the current and the impressed e.m.f. depends 

 on the field excitation. In Fig. 250 



OE = E = impressed e.m.f., which remains constant. 



01 = I = armature current in phase with E. 



OEi = EI = Ir = e.m.f. consumed by the resistance of the 



armature, in phase with /. 



OEi" = E" = jlx = e.m.f. consumed by the synchronous 

 reactance of the armature, 90 degrees ahead 

 of/. 



