THE CONTINUOUS CURRENT GENERATOR 135 



above or below the voltage at which the lamp is rated. 

 Now if the terminal voltage of the generator should remain 

 constant, the voltage of points on the distributing system 

 must fall as the load is increased due to increased IR drop 

 in the wires of the distributing system. 



In Fig. 86 this point is illustrated. A group of lamps 

 is connected to a center of distribution B; the generator 

 is located at A. If the voltage at A remains constant 

 as the load increases, it is evident that the voltage at B 

 must fall because it is always equal to the voltage at A 

 minus the drop in the line AB. But if the increase in 

 voltage at A, from no load to full load, is just equal to 

 the IR drop in AB when full load current is flowing, then 



Generator 



Fia. 86. Elementary Diagram of a Power Distribution System. 



the voltage at B will be the same at full load as it is at no 

 load. At intermediate loads the voltage at B will be some- 

 what above normal ; the external characteristic of a generator 

 is always more or less curved (due to the variable reluc- 

 tance of the magnetic circuit) so that if the machine is prop- 

 erly compounded at full load it is always somewhat over- 

 compounded at half load. This effect is not enough to 

 cause any trouble on the system. 



Series and shunt wound generators are used but very 

 little in practice. Some special arc light machines employ 

 series excitation but their use is not extensive. 



The difference between the no-load terminal voltage and 

 full-load terminal voltage (field excitation and speed con- 

 stant) expressed in percentage of the full-load voltage is 



