340 



PRINCIPLES OF ELECTRICAL DESIGN 



tion curve for air gap, teeth and slots need be drawn. This 

 curve (Fig. 139) is constructed as explained in Art. 42, the con- 

 struction having previously been illustrated in connection with 

 the example in dynamo design (item (71), Art. 63, Chap. X). 

 The ampere-turns per inch length of tooth are read off Figs. 

 3 and 4; and SIMPSON'S rule (see Art. 38, formula 64) is used in 

 calculating the ampere-turns required for the rotor teeth at the 

 higher densities. In regard to the stator teeth, the mean value 

 of the tooth density may be used in determining the ampere- 

 turns required; the application of SIMPSON'S rule being in this 



8000 



10000 12000 14000 16000 18000 20000 22000 24000 26000 

 Ampere Turns per Pole 



FIG. 139. Saturation curves for air-gap teeth, and slots 8000 k.v.a. 



turbo-alternator. 



case an unnecessary refinement. 1 In calculating the tooth 

 reluctance for plotting the saturation curve Fig. 138, no correc- 

 tion for. leakage flux has been made. It is true that the total 

 flux in the body of the rotor is somewhat greater than the useful 

 flux entering the armature; but the omission of this correction 

 may be set against the fact that the tooth density calculations 



1 In most cases, the practical designer who cannot afford to spend much 

 time on refinements of calculation calculates the density at a section 

 one-third of the tooth length measured from the narrowest end, and he 

 uses this value in getting an approximate average value of H from the B-H 

 curve. 



