103 



exciting wire, and the exciting current is 

 28 amperes. This gives an exciting 

 power of 7,300 ampere turns, and the 

 calculated strength of field is 144 English 

 ines. Allowing for self-induction and 

 resistance, the induced electromotive 

 force may be taken as 2,050 volts. A 

 continuous-current machine of the same 

 iimeneions and winding would give 900 

 volts ; so that for this machine, as 

 arranged to produce an alternating cur- 

 rent, the coefficient is k = 2.280. The 

 width of the field, allowing for the fringe 

 3f lines round the pole pieces, is 0.55 of 

 the pitch, and the surface covered by the 

 active wires in the armature-coils is 0.55 

 of the whole surface. Theory would there- 

 fore indicate that the coefficient must be 

 very nearly that given for case 5, p. 22, 

 uamely, 2.300, which is indeed the case. 

 In a 150-kilowatt machine of the same 

 type, the output is 75 amperes at 2,000 

 volts pressure; the speed being 500 

 revolutions per minute, and the frequency 

 100. There are twenty-four poles, and 

 the number of active wires is six hun- 



