D.  C.  COMMUTATING  MACHINES 


173 


FIG.  86. — Multiple  double  spiral  full  pitch  winding. 


FIG.  87. — Multiple  double  re-entrant  drum  full  pitch  winding. 


174     ELEMENTS  OF  ELECTRICAL  ENGINEERING 

Figs.  88  and  89.  Fig.  88  shows  a  part  of  a  series  drum  winding 
developed.  Coils  C\  and  C2,  having  corresponding  positions  under 
poles  of  equal  polarity,  are  joined  in  series.  Thus  the  end  con- 
nection ah  of  coil  Ci  connects  by  cross  connection  be  and  cd  to  the 


FIG.  88. — Series  lap  winding. 

end  connection  de  of  coil  C%.  If  the  armature  coils  consist  of  a 
single  turn  only,  as  in  Fig.  86,  and  thus  are  open  at  6  and  d}  the 
end  connection  and  the  cross  connection  can  be  combined  by 
passing  from  a  in  coil  Ci  directly  to  c  and  from  c  directly  to  e  in 


FIG.  89. — Wave  winding. 


coil  C2;  that  is,  the  circuit  abcde  is  replaced  by  ace.     This  has 
the  effect  that  the  coils  are  apparently  open  at  one  side. 

Such  a  winding  has  been  called  a  wave  winding.  Only  series 
windings  with  a  single  turn  per  coil  can  be  arranged  as  wave 
windings,  while  windings  with  several  turns  per  coil  must  neces-