98 



PRINCIPLES OF ELECTRICAL DESIGN 



ance between the coils. This clearance need be provided only 

 in high-pressure machines, or when it is desired to improve 

 ventilation. For approximate calculations on machines up to 

 600 volts, the angle a may be calculated from the relation 



1.15s 

 Bin a = 



In practice the angle a usually lies between 35 and 40 degrees. 

 The length of the straight part AC (Fig. 33) is where BA 



COS a 



T . 



is half the coil pitch, or ~ in the case of a full-pitch winding. 



FIG. 33. End connections of armature coil. 



The portion of the end connections between the end of the 

 slot and the beginning of the straight portion AC is about % 

 in. in low-voltage machines, increasing to 1 in. in machines 

 for pressures between 500 and 1,000 volts. The allowance for 

 the loop where the coil is bent over to provide for the lower half 

 of the coil clearing the upper layer of conductors will depend 

 upon the depth of the coil-side and therefore upon the depth of 

 the slot. If d is the total slot depth, in inches, an allowance equal 

 to 2d will be sufficient for this loop. The total length of coil 

 outside the slots of a low-voltage armature will therefore be 



(52) 



where T must be taken to represent the coil pitch instead of the 

 pole pitch if the winding is of the chorded or short-pitch type. 



