272 



ARMATURE CONSTRUCTION 



section is shown in Fig. 322. There are eight conductors 

 per slot, and each conductor measures 12*0 mm. X 2-5 mm. A 

 developed plan of a portion of the winding is given in Fig. 323. 

 The first question to be decided is whether we shall have 

 a joint at the back end, or whether we shall have a con- 

 tinuous strip for the complete turn, thus having only joints 

 at the front end. The arguments in favour of joints at 

 both ends are based on the fact that windings are more fre- 

 quently found defective on those parts nearest the surface ; 

 moisture condensation and transportation difficulties are some- 

 times responsible for this. Then, again, if the windings are in 

 halves, the bottom layers may be securely fastened down on to 



Insulation // . 

 InsukUd Conductors, 



Bare Conductors. 



FIG. 322. Section of Slot of 250 k.w. 550-volt Generator. 



the end-supporting flanges before the upper portions of the coils 

 are put in place. This argument is perfectly sound in the case 

 of turbo -generator armatures, and in high-speed machines in 

 general. 



The arguments in favour of jointless windings are based 

 on the saving in time and money, and the avoidance of pos- 

 sible poor soldering in the joints and of scattered drops of 

 solder in the windings. Jointless windings may save as much 

 as 20 per cent, in time of making and assembling coils on the 

 armature, and the absence of joints gives a greater security 

 from breakdown. 



This latter is the preferable plan in the present instance. By 

 scaling off from the drawing, we find that the total length of 

 one turn from beginning to end is 230 cms. The armature has 

 altogether 600 turns; hence we must first cut up 600 strips of 



