Fig. 1,758.—Field construction of Crocker-Wheeler induction motor with magnetic bridge. Steel bridges are inserted in the grooves where the coils are placed, to protect them from dirt and mechanical injury and at the same time provide a path for the magnetic flux which has a more uniform reluctance, thereby insuring a better distribution of the flux in the air gap and at the same time retaining open slot construction from which the coils can be readily removed.
Ques. What is the general character of the field winding?
Ans. The field core slots contain a distributed winding of substantially the same character as the armature winding of a revolving field polyphase alternator.
Ques. Are the poles formed in the usual way?
Ans. They are produced by properly connecting the groups of coils and not by windings concentrated at certain points on salient or separately projecting masses of iron, as in direct current machines.
Ques. How are the coils grouped?
Ans. Three phase windings are usually Y connected.
Fig. 1,759.—Western Electric squirrel cage armature. The inductors consist of solid copper bars embedded in the slots of a laminated core, with their projecting ends securely fitted and soldered to heavy copper rings.