38 
DIRECT-CURRENT .DYNAMOS AND- MOTORS. 
352. 
353. 
354. 
355. 
356. 
35%. 
358. 
359. 
360. 
361. 
362. 
363. 
ture rise, 45° C.; all coils of both series and shunt wind- 
ing to be connected in series. 
Assuming that the magnetizing force required for the 
generator given in Question 300 was found to be 
42.000 ampere-turns, determine a shunt -winding for a 
temperature increase of 30° C., allowing 10 per cent. of 
the terminal E. M. F., which is 600 volts, for regu- 
lating resistance; coils connected in series. 
From the data given for a 1,500 K. W. railway generator 
in Question 300, compute a compound winding for a 
rise of 25° C., provided that the speed is 250 revolutions 
per minute and the armature resistance .00240ohm. The — 
series coils to be connected in two groups and the shunt 
coils in three groups. 
Define electrical efficiency. 
Define commercial efficiency. 
Define gross efficiency. 
Give the general formula for the electrical efficiency of a 
generator. 
State the general formula for the electrical efficiency of a 
motor. 
By what formula is the electrical efficiency of a series- 
wound generator calculated? 
Give formula for the electrical efficiency of a shunt-wound 
generator. : 
Give formula for the electrical efficiency of a compound- 
wound generator. 
How do the efficiency formulas for a motor differ from 
the corresponding formulas for a generator? 
Express the armature current of a shunt or compound- 
wound generator, and that of a shunt or compound- 
wound motor, in terms of the terminal and shunt cur- 
rents. 
