98 



ARMATURE CONSTRUCTION 



the slots ; and secondly, the fixing of the end rings which short- 

 circuit the bars at each end of the core. So far as the securing of 

 the bars in the slots is concerned, this is easily accomplished by 

 packing them tightly with a layer of some suitable insulating 

 material such as red fibre or leatheroid. 



The method of fixing the end rings depends somewhat on the 

 shape of the section of the conductors. Below are given several 



FIG. 105. Squirrel Cage Rotor. Lancashire Dynamo Co. 



good types of construction for both round bars and bars of rect- 

 angular section. In modern designs there is a tendency to 

 increase the total amount of copper on the rotor for various 

 reasons in connection with the design and performance of the 

 motor, into a discussion of which we have no occasion to enter 

 now. In such designs the total cross section of each bar becomes 

 larger and larger, and it is necessary to use slots having a radial 

 depth great compared with their width, in order to get room for 

 the required amount of copper on the periphery. 



In cases where a round bar, and, consequently, a circular slot, 



