CHAPTER IV 

 THE CONTINUOUS CURRENT MOTOR 



29. Relation between Generator and Motor. As has 

 been said before the c-c. generator and the c-c. motor 

 are nearly identical in construction; the construction which 

 is best for one is generally best for the other; a machine 

 which runs well as a generator will generally operate satis- 

 factorily as a motor. 



Difference in Operation. Although the construction 

 of the two is practically the same the operation of one 

 machine differs quite materially from that of the other c 

 The generator is always rotated by some prime mover at 

 a speed as nearly constant as possible. The motor, on the 

 other hand, has no prime mover but is supplied with 

 electrical power instead of mechanical power as is the case 

 with the generator. The speed of an electric motor is gen- 

 erally not constant as the load is varied; in some cases 

 this speed variation may be small while in others the highest 

 speed of operation may be several times as great as the 

 lowest speed. 



The function of a generator is to generate an e.m.f. 

 by moving conductors through a magnetic field while the 

 prime function of a motor is to produce a turning effort, 

 or torque. 



- Torque Acting in a Generator. When a machine is 

 operating as a generator and its armature is carrying cur- 

 rent, it too, develops a torque (because the armature con- 



150 



