322 



ELECTRICAL EQUIPMENT 



tending to retard the machine of the higher speed and accelerate 

 the machine of the slower speed, thus tending to hold the machines 

 in synchronism at a speed corresponding to the load. The 

 division of the load between the units depends then only on the 

 action of the governors, and it is seen from the curves that at a 

 load c, the machines will divide the load equally. For other loads, 

 the ratio will be different, for example, at a certain lighter load 



the ratio may be ~. while for a certain heavier load it may be -=-^. 

 oo oo i 



The division of load between two alternators depends, there- 

 fore, as stated, primarily upon the speed-load characteristics of 

 the prime movers, the governors of which must be adjusted for 



FIG. 188. 



a definite drop in speed from no load to full load. With flat speed 

 characteristics the division of the load will be of an unstable 

 nature. By adjusting the field 4he form of the energy delivered 

 by the generator can be changed but not the amount. What 

 really occurs with a change in field adjustment of any piece of 

 synchronous apparatus operating in parallel with another, is a 

 change of the power factor of that machine. 



The above refers also to different stations operating in parallel 

 on the same system, and the division of load and wattless current 

 between the stations must, therefore, be handled differently. On 

 a network supplying power over a large territory, the power factor 

 will often be low and there will be considerable wattless current 

 to be taken care of. 



