PROBLEMS. 503 



205. Given the following data specifying the external char- 

 acteristic of a shunt generator : 



E x 216 207 197 187 175 161 146 volts. 

 f a o 4 8 12 16 20 24 amp. 



The resistance of the armature is 0.4 ohm and the resistance of 

 the shunt field winding is 116.7 ohms. Plot the external char- 

 acteristic from the above data, and derive and plot the total char- 

 acteristic, ignoring the demagnetizing action of the current in the 

 armature. Ans. Coordinates of one point, E a = 182 volts, 

 / a = 17.5 amperes. 



206. Derive the data for the external ampere-ohm character- 

 istic of the shunt generator of problem 205 and plot the external 

 ampere-ohm characteristic of the machine. Ans. Coordinates 

 of one point, /. = 16 amperes, R x = 10.94 ohms. 



207. Given the following data for the magnetization curve of a 

 shunt generator at a speed of 1,200 revolutions per minute : 



- 7 I -S l 3%- i85-0 209.5 221 5 232.5 242.0 250.5 258.0 

 / 0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 5.4 



Plot this magnetization curve and derive from it the voltage-speed 

 characteristic of the machine at zero load, the resistance of the 

 shunt field winding being 80 ohms. Armature resistance ignored. 

 Ans. Coordinates of one point, 430 volts at 2,000 revolutions 

 per minute. 



208. Derive the total characteristic of the shunt generator of 

 problem 207 from its magnetization curve, the resistance of the 

 armature being o. 1 5 ohm Ignore the demagnetizing action of 

 the current in the armature. Ans. Coordinates of one point, 

 E a = 209.2 volts, 7 o = 1 14.7 amperes. 



209, (a) A short-shunt compound generator, rated as a 1 10- 

 kilowatt machine, is 10 per cent, overcompounded. That is, it 

 gives between its terminals 500 volts at zero load and 5 50 volts 

 at full load. Plot the external characteristic of the machine, 

 assuming it to be a straight line between zero load and full load. 



