24 ELECTRICAL MACHINERY 



Application of Formula. From the above formulae the 

 torque developed by any motor is easily calculated. If 

 the strength of the motor field is known, and if the cur- 

 rent flowing through the armature conductors and the 

 total length of conductor on the armature which lies in 

 the magnetic field are measured, the pull at the periphery 

 of the motor armature is then obtained by formula (15). 

 Then if the speed of rotation of the motor armature is 

 known, the horsepower of the motor is easily calculated. 



12. Principles Involved in Operation of the Motor and 

 the Generator. A dynamo-electric machine is a machine 

 which may be used to convert mechanical power into 

 electrical power, or vice versa. A dynamo-electric machine 

 which is made to revolve by the application of mechanical 

 power, and which supplies electrical power to some outside 

 circuit is called an electric generator, or merely a generator. 

 A dynamo-electric machine to which is supplied electric 

 power, causing it to revolve and furnish mechanical power to 

 some load, is termed an electric motor, or merely a motor. 

 In so far as their construction is concerned the two types 

 of machine are practically identical. The same machine 

 will often serve either purpose; a machine which, run as 

 a generator, will give 5 kilowatts of electrical power at a 

 voltage of 110 volts, would, if connected to a 110 volt supply 

 line, run as a motor at about the same speed it previously 

 had as a generator and would have an output capacity 

 of about 5 horsepower. 



Of course it must not be supposed that all machines 

 which operate satisfactorily as motors will serve equally 

 well as generators, or vice versa. Thus a motor df the type 

 used in railway service (known as a series motor) might 

 not operate as a generator at all; or at best its operation 

 would be more or less unsatisfactory. Other types of 

 machines, however, operate equally well for either purpose. 



Principle of the Generator. The principle involved in 

 the operation of an electric generator may be briefly stated 



