146 



ELECTRICAL MACHINERY 



bus-bar e.m.f.; when the generated and terminal e.m.fs. 

 of a machine are the same there can be no current flowing 

 through its armature. When the load is zero, the generator 

 switch is opened and then the generator may be stopped. 

 When it is necessary to connect an additional generator 

 to the bus-bars, due to load increase, its terminal voltage 

 is first made equal to the bus-bar voltage then the generator 

 switch is closed; the machine will take no load on closing 



Feeders 



Main Busses 



\ 



Equallzer'Bug 



No. 2 



No. 1 



FIG. 93. Elementary Diagram of Station Connections for Two Com- 

 pound Generators in Parallel. 



the switch but its load may be brought to any derired 

 value by decreasing the resistance of its field circuit. 



Load Division with Compound Generators. When over- 

 compounded generators are operated in parallel, it is neces- 

 sary to install an extra bus-bar called the equalizer bus-bar. 

 The diagram of two compound generators, connected for 

 parallel operation is shown in Fig. 93. 



Without this equalizer bus the parallel operation of two 

 compound generators is unstable; they will not divide 

 the load equally but on the contrary one machine will stop 



