46 



ELECTRICAL MACHINERY 



is the part that revolves. This type of armature core 

 is used on practically all large a-c. generators and motors. 



Shape of Slots. The shape of the slot is determined 

 by various factors in the design, and somewhat by the kind 

 of winding with which the armature is to be supplied. In 

 case a formed coil is to be used an open slot is likely to 

 be used as shown in Fig. 21 (a) ; after the coil has been 

 slipped into place in the slot a wooden wedge (shown in 

 the second slot of (a)) is driven in place to hold the coil 

 securely in the slot. Most machines use a semi-closed slot, 

 as shown in Fig. 21 (6) and (c). It is evident that a formed 

 coil could not be forced into slot (b) very easily. The coil 

 may be fitted into such a slot by having the coil only par- 



6 c 



FIG. 21. Various Forms of Slots. 



tially formed; that part of the coil which is to be pushed 

 into the slot is left untaped so that the wires forming the 

 coil can be separated and pushed into the slot one by one. 

 A small machine being wound with these partially formed 

 coils is shown in Fig. 22. The method of placing the coils 

 in the slots is apparent. 



An armature having slots of the shape shown in (c) Fig. 

 21 may be wound with a completely formed coil if there 

 are to be two coil sides per slot in the winding. The coils 

 lie in the slot side by side as indicated. The coil marked 

 (2) is first pushed in through the narrow opening in the 

 slot and then pushed to the right to make way for coil 

 1 which is then put in place. 



