186 



ELECTRICAL MACHINERY 



of Fig. 112 is equal to OE of Fig. 113. At the time t 2 the 

 power demanded by the load is less than the input to the 

 motor and so the motor begins to speed up and to increase 

 the energy stored in the flywheel; the current begins to 

 decrease at the same time. At the time fe the motor has 

 regained its original speed of 1000 r.p.m. and the current has 

 fallen to the value OD. The single-hatched area in Fig. 112 

 represents the amount of energy which the retarding 

 flywheel gives up when the load is heavy and the double- 



Current U t 



FIG. 113. Speed-load Curve of Heavily Compounded Motor. 



hatched area represents the energy which the motor returns 

 to the flywheel when the load is light; these two areas are 

 equal. 



This use of a heavy flywheel to equalize the input to a 

 motor supplying an intermittent load is becoming quite 

 general; it decreases the size of motor required and makes 

 the operation of the generating station much easier. This 

 last consideration is of importance only when the size of 

 the motor is somewhere near that of the generator supply- 

 ing its power. 



