: THE SYNCHRONOUS CONVERTER 369 



four parts. T/I/.S scctionalizing switch should be open when Parting 

 from thr alternating-current side. 



If there be a switch short-circuiting the series field, this should 

 be opened, as otherwise the currents generated in tin- scries field 

 by the transformer action of the armature will cause undue heat- 

 ing. If there be a series-field shunt or diverter, this should be 



- I for the same reason. 



The rotating field produced by the armature n//x the armature 

 conductors, Fig. 335, just as 

 if the armature were rotat- 

 ing and cutting the flux of a 

 stationary field, as in the 

 direct-current generator. 

 This field induces voltages 

 in the armature coils. Some 

 of these coils are short- 

 circuited by the brush 



-parking results under 

 the brushes, even though 

 then' is no direct-current 

 load. This sparging may 

 not be severe, as the rotat- 

 ing field is Comparatively Fl0 ' 336 - Connections of shunt field and 



hunt field-splitting switch. 



k m the inter polar 



- where the brushes are, because of the high reluctance of 



the air path at these points. However, if intrrpnles are used, 



tin- reluctance of the interpolar space is reduced very materially 

 so that sparkinir beoomefi -< vere. Consequently, brush-raising 

 devices are usually installed on interpole machines, to lift the 

 bru-he< on starting and >o eliminate this sparking. One brush 

 in a ! bru^h-holder and one bru-h in a negative bru-h- 



Imlder are usually left on the commutator to supply the field 

 xcitation. In order to reduce the sparking caused by thoe 

 two bru-hes short -circuitng armature coil> in which electromotive 



- arc induced by the rotating field, these brushes are nt'ten 



<O that the time oi < irciiiting is reduced t<> a 



minimum. ( '<.n\ i at reduced volt 'lined 



from tap- nn tl , rt ing 



compensators are used at times in the units of smaller si 



Field-Reversing 

 Switch 



