154 



THE MAGNETIC CIRCUIT 



[ART. 49 



B 



dilations it is advisable to use at least 0.30. When a synchronous 

 motor is working near the limit of its overload capacity, the influ- 

 ence of the distorting ampere-turns is particularly important, and 

 in estimating the overload capacity of a synchronous motor it is 

 better to be on the safe side and to take the value of the numerical 

 coefficient in eq. (81) somewhat higher than 0.30. The value of 

 this coefficient varies within wider limits than that of the corre- 

 sponding coefficient 

 in formula (79) ; 

 but, fortunately, it 

 affects the perform- 

 ance to a lesser de- 

 gree (see Art. 51). 



49. TheBlondel 

 Performance Dia- 

 gram of a Syn- 

 chronous Machine 

 with Salient Poles. 

 Having replaced the 

 actual armature 

 reaction by two 

 m.m.fs. M d and M t 

 (Fig. 39) the elec- 

 tromagnetic rela- 

 tions in the machine 

 become those indi- 

 cated in Figs. 40 and 

 41. Fig. 40 refers 

 to a generator and 

 is analogous to Fig. 

 37; Fig. 41 refers 

 to a motor and is 

 analogous to Fig. 



38. The polygon OABD, which represents the relation between 

 the terminal and the induced voltages, is the same as before, but 

 the induced voltage E is now considered as a resultant of the 

 voltages E n and E t induced by the real and the fictitious poles 

 respectively. 1 In the generator the fictitious poles lag behind 



1 The subscript n stands for net, to agree with the m.m.f. M n used later 

 on; the subscript t stands for transverse. 



FIG. 40. Tho performance diagram of a synchro- 

 nous generator, with salient poles. 



