164 



ELECTRICAL ENGINEERING 



where n is the speed in r.p.s. = % 8 <r> 



Z is the number of armature conductors = 512, 

 $ g is the flux crossing the air gap, 

 p is the number of poles = 6, 



Pi is the number of paths in parallel through the arma- 

 ture winding = 6, 

 & is the terminal voltage at no load; 



and c 

 therefore, 



or 



S-512XWXHO-**., 



= 42,000 6. 



-7.75 



Section 

 80 Sq.In 



FIG. 130. Magnetic circuit of a dynamo. 



To produce the rated voltage, 150 volts, a flux is required in the 

 air gap of 42,000 X 150 = 6,300,000 lines. 



The leakage factor of this machine would be about 1.2, so that 

 the flux required in the poles is 



$ p = 1.2$,= 1.2 X 6,300,000 = 7,560,000 lines. 



The following table (Fig. 131) gives the values <t> p and $ g for 

 values of terminal voltage from to 175 volts, assuming that the 

 leakage factor is constant. 



The next step is to determine the lengths and sections of the 

 various parts of the magnetic circuit and the ampere turns re- 

 quired per pair of poles to drive the flux through them. 



The yoke is made of cast iron and has a section of 80 sq. ins. ; the 

 length of the magnetic path through it is taken as the estimated 



