THE CONTINUOUS CURRENT GENERATOR 



series field of machine No. 2 increases and if this field cur- 

 rent increases the voltage of No. 2 must increase also. 

 Hence any increase in voltage of No. 1 is accompanied by 

 an increase in the voltage of No. 2 and therefore No. 2 will 

 continue to furnish its share of the load. 



It was noticed that without the equalizer bus when 

 No. 1 increased its load (and thereby its voltage) the volt- 

 age of No. 2 decreased and this was the cause of the unstable 

 operation; when the equalizer bus is used, however, if 

 No. 1 increases its load the voltage of No. 2 increases also, 

 thereby causing No. 2 to continue to carry its share of the 

 load. 



Another way of looking at the same problem is to notice 

 that the two series fields are put in parallel by the use of 

 the equalizer bus and so any increase in one field must be 

 accompanied by a corresponding increase in the other. 



If two compound generators of equal capacity are to 

 operate in parallel and divide the load equally, they must 

 have identical external characteristics and the resistances 

 of their series field circuits must be equal. We say series 

 field circuit instead of series field because generally 

 the series field is paralleled by a shunt and it is the 

 resistance of the double circuit, series field with shunt in 

 parallel, which must have the same value for both machines. 



Compound Generators of Different Capacities. If two 

 compound generators of unequal capacity are to operate 

 well in parallel, dividing the load according to their capac- 

 ities, the two machines must be adjusted to give the same 

 no load and full load voltages and the resistances of the two 

 series field circuits must be inversely proportional to their 

 capacities. This last condition evidently is fulfilled if the 

 full load IR drop is the same for each series field circuit. 



