94 THE DIRECT-CURRENT M<>T(>if CH. V 



CHARTER V 



SERIES-WOUND MOTORS 



WHEN the magnets of a dynamo are connected in 

 series with the armature, the induction factor will 

 vary with the current. In Fig. 20 distances measured 

 along ob represent current in the armature, and also in 

 the magnets. We will take 500 volts as the tension of the 

 line, 5 ohms as the resistance of the motor, the maximum 

 current being thus smaller than 100 amperes. Let the 

 distance 01 represent 100 volts, 10 amperes, 100 r.p.m., 

 1,500 inch-pounds of torque, and an induction factor of 15. 

 Let oa represent the tension of the line, ob the maximum 

 possible current. Join la, and produce it. We shall call 

 ba the loss line, since the intercept kc of any ordinate 

 between it and a horizontal line through a gives the volts 

 lost in heat. On ob construct the induction curve. Thus, 

 if for a current of 70 amperes, the induction factor is 

 67 - 5, we must set up on the point representing 70 

 amperes in the armature, a vertical distance equal to 

 4*5 inches, and this will be a point on the induction 

 curve. 



If there is no residual magnetism the induction factor 

 is nothing when the current is nothing. When the 

 current is reversed the induction factor will also be 



