(-H I THK IN: it)R 17 



baft when a current of 300 amperes is passed through 

 the armature i- tl.- inch-pou 



Example 10. -A generator is running at i ID r.p.m. 

 The tension on the brunhes It.s when tin- machine 



in delivering 100 amperes. The internal resistance of the 

 armature is 0-0370 ohm. What i- the pull on the U-lt 

 due to the current in the armature if the pulley is 40 

 inches diameter ? The beat drop is !' volt>, so that the 

 uduced tension is 060, and M i> 77. The pull due to 

 the armature current is e<|iia! to Uie tonjue dmd.-d by tbo 

 radius of the pullry,or J.I <J<> pound*. I f we had neglected 

 the heat dmp. the pull would have appeared t I 

 pounds less than this. 



The induction factor can be varied by changing the 

 current in the magnets. We may obtain values of 

 different values of the magnetising current by cither of 

 the methods previously described, the torque <>r the speed 

 method. If the values of M are plotted on a base of 

 current in the magnets, we get a curve that we shall call 

 the induction curve.' 



_r. 8 gives the induct inn curve of the an- light 

 dynamo already described, obtained by running the arma- 

 ture at a measured speed and observing the induced 

 tension on open rireuit t'>r different currents in the magneto. 

 The curve plutted in the H^un- is for descending values of 

 the current. 



The curve commonly called the ' Characteristic ' may 

 be obtained from the induction curve by multiplying the 

 vertical animates by any given numU-r >i revolutions per 

 second, thus giving a curve of volt** for the given speed on 

 a base of magnet current. The it curve U <|uite 



independent of speed, since it represent* the 



C 



