348 



PRINCIPLES OF ELECTRICAL DESIGN 



very closely represented by the addition of two curves similar to 

 Fig. 143 with a phase displacement of 60 degrees, as pointed 

 out on page 291. 



As a check on the work, it should be noted that if the e.m.f. 

 wave shape (Fig. 143) had been a true sine-wave, the virtual 

 value of the apparent developed voltage would have been 3,605 X 

 1.11 = 4,000, which proves the accuracy of the graphical work. 

 It is not, however, suggested that a difference of 1 per cent, in 

 the form factor is a matter of practical importance; but in salient- 



FIG. 145. Diagrammatic representation of flux lines in turbo-alternator. 



pole machines with incorrectly shaped pole faces and a con- 

 centrated armature winding, the wave shape may depart very 

 considerably from the sine curve, and it is under such condi- 

 tions that the methods here illustrated will be of the greatest 

 value. 



The area of one lobe (Fig. 144), using 1 volt as the unit radius 

 vector, is 24,700,000, and the maximum ordinate of the equiva- 

 lent sine-wave, as given by formula (108), is 



X 24,700,000 



= 5,600 volts 



