CH. I THK IMMVTInN l-ACTd; 7 



Example 4. A four-pole motor has its annat mi- 

 series connected, with 2-8 x 1C 6 lines per pole and 600 

 surface conductors. The induction factor is 33'6. 



When M is known the torque for any current can at 

 one*' be obtained from Equation 5. 



Example 5. A motor has an induction factor of ">. 

 Tin- torque on the shaft for 90 amperes in the armature is 

 <!:>') inch-pounds. 



In estimating A we have to count round the entire 

 surface of the armature, and include only those conductors 

 which, being adjacent, are also in series with one another. 

 In many cases one ' conductor,' according to our nota- 

 tion, is, for convenience, made up of two or more in- 

 sulated wires in parallel, so that in counting we must be 

 careful not to reckon as two conductors two adjacent 

 \\iivs which are connected in parallel with one another. 



Example 6. A railway motor has 60 slots on the 

 armature, and 21 wires per slot, every two of which are in 

 parallel, giving 12 'conductors' per slot, and making 

 .1=720. 



In a ring-wound armature each tuni after leaving 

 the end of the armatuf e away from the commutator passes 

 in-itlf the armature, where it does not cut any lines of 

 force, and so back to the next bar. Hence one- turn per 

 commutator bar with a ring armature means as many 

 surface conductors as there are bars; four turns per liar 

 means four times as many surface conductors as there are 

 bars, and so on. 



In :i drum armature, however, each turn after passing 

 up the armature from the commutator, is brought back on 

 the surface of the armature, and finds its way to the next 

 bar without passing inside the armature; hence each 



