MAGNETIZATION CURVES 29 



Note the difference in these two cases due to the shape of th<- 

 curve. 



4. Plot a curve to show the effect on the magnetization curve 

 of using in problem 1 a toothed core armature with a clearance of 

 0.3 cm. Assume the teeth to be 1.5 cm. long and to occupy 50% 

 of the area under the pole face. (80 min.) 



5. To maintain the same voltage in the generator of problem 

 2, if its speed were to be decreased to 425 r.p.m., what change in 

 the field ampere-turns would be necessary? Also if the q 

 were to be increased to 475 r.p.m.? (5 min.) 



6. The machine of problem 2 has an armature resistance of 

 0.0081 and the equivalent demagnetizing turns on the armature 

 are 28. Determine from the magnetization curves the ampere- 

 turns and the field current necessary to operate the machiin at 

 full-load current and voltage. Also the voltage necessary on t In- 

 field to give this field current, the shunt-field resistance being 

 61 ohms. Could the generator be operated as a plain shunt 

 machine? (4 min.) 



7. Determine from the data given in problem 6 the number of 

 series turns needed to operate this machine as a flat compound and 

 also as a 10% over-compound generator. (3 min.) 



