" OF APPLIED SCIENCE. 



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BIPOLAR DIAGRAM 



157 



directions show clearly the relative angular positions of the two 

 revolving fields, being the coupling angle as before. 



Also the torque-producing mechanism (the flux represented by 

 RI, the armature ampere- turns represented by AI, and their phase 

 difference) is a little more obvious. 



In both E.M.F. and M.M.F. diagrams the line OB is in length 

 proportional to the armature current, and the angle <J> designates 

 the phase difference between armature current and impressed E.M.F. 



In the case of a normal machine, the armature resistance is small 

 as compared with the synchronous reactance X, and the constant- 

 power circles flatten out almost to straight lines (see Fig. 78). 



Example. In Fig. 77 are shown the saturation and short-circuit 

 curves of a three-phase 60 H.P. 44o-volt synchronous motor. 



The M.M.F. diagram is shown in Fig. 78 and the phase charac- 

 teristics in Fig. 79. If the abscissae of the phase characteristics, 

 determined from the E.M.F. diagram, were to be transformed from 

 E.M.F. to field current through the medium of the saturation curve, 



