248 



ARMATURE CONSTRUCTION 



Figs. 285 and 286 are instances of the preferable design for 

 armature slots in which wedges 'are dispensed with. The use of 

 wooden wedges is at present coming to be restricted to the 

 external stators of induction motors with open slots, for in this 

 case, use cannot, of course, be made of binding wires. Fig. 287 

 gives an instance of such a slot. 



Mica and micanite should only be employed for slot linings 

 in high-voltage machines. Pertinax and micarta and presspahn- 

 mica are all good alternatives in suitable cases. 



Insu/xC-ion I M/c* 

 d Co Horn Fibre. 



03mm 

 Emire, Clobh- 4 laers 0/78 mm 



B-rc 

 DCC 



V^rn/s k Q'i>5 



3' J?5 mm 

 3-55 mm 



FIG. 285. Section through Slot of Wire-wound Continuous-current Armature. 



For materials to be employed in binding the conductors together 

 in groups, and for the wrapping for armature bars, one or more of 

 the materials given in the following list may be employed : 



Cotton tape (sometimes known as "jaconet" tape, and 



generally 0*13 mm. thick). 

 Varnished cambric. 



Manilla paper, impregnated with insulating varnish. 

 Oiled unbleached cotton. 

 Mica paper. 



From this variety a suitable choice will ensure good results if 

 care is used in the preparation and application. A few examples 

 from practice will be of service. 



