I-A] 



SERIES GENERATOR. 



multiplied by the assumed constant speed and divided by the 

 observed speed. 



10. Curve. After the speed correction is applied, the magne- 

 tization curve is plotted as in Fig. 3. The abscissae of this curve, 

 field amperes, are proportional to field ampere-turns or magneto- 

 motive force; the ordinates, volts generated at constant speed, 

 are (by Faraday's principle, i) proportional to magnetic flux. 

 The curve, therefore, is a magnetization curve (showing the 

 relation between magnetic flux and magnetomotive force) for 

 the magnetic circuit of the generator, which is an iron circuit 

 with an air gap. The bend in the curve indicates the saturation 

 of the iron. 



n. External* Series Characteristic. This characteristic, 

 which is the operating or load characteristic of the machine, shows 

 the variation in terminal 

 voltage for different cur- 

 rents, when the machine is 

 self excited and the exter- 

 nal resistance is varied. 

 The armature, field and 

 external circuit are in 

 series, as in Fig. 2; read- 

 ings are taken of current, 



FIELD 



ARMATURE 



FIG. 2. 



Connections for series character- 

 istic, self excited. 



The 



voltage and speed, for an ascending curve as in Fig. 3. 

 descending curve may be taken if desired. 



For any point on the curve, the resistance of the external cir- 

 cuit is R = E -f- 7, or the tangent of the angle between the /-axis 

 and a line drawn from the point to the origin. Below the knee 

 of the curve, it will be seen that a small change in the external 

 resistance will make a large change in current and voltage. 



* ( na.) In any characteristic the term "external" indicates that the 

 values of current and voltage external to the machine are plotted ; the term 

 41 total " indicates that the total generated armature current and voltage are 

 the quantities used. 



