SYNCHRONOUS MACHINERY 



287 



which the regulator is adjusted, the main contacts open again, the 

 relay magnet is again magnetized and the short-circuit on the 

 exciter field rheostat is opened. This reduces the voltage as before 

 and the cycle of operations is repeated at a very rapid rate and 

 maintains a constant voltage at the terminals of the alternator if 

 the compensating winding is not connected. 



FIG. 262. Automatic voltage regulator for alternators. 



When it is necessary to maintain a constant voltage at the 

 receiver end of the line the compensating winding is connected as 

 shown. As the load increases it brings the main contacts closer 

 together and so increases the time of short circuit of the field' 

 rheostat and thus increases the terminal voltage of the alternator. 

 Using a current transformer and a dial switch any line drop up to 

 15 per cent can be compensated for, but only at a given power 

 factor. When the power factor of the load varies through a wide 

 range a line compensator, Fig. 263 (a), should be used in conjunc- 

 tion with the potential coil and the compensating coil should be 

 disconnected. 



The line compensator forms a local circuit with the same voltage 

 characteristics as the main line. The shunt transformer TI gives 

 a secondary voltage proportional to the generator voltage. The 

 current transformer T% produces through the circuit rx a current 

 proportional to the load current, r is a resistance which consumes 

 a voltage proportional to and in phase with the resistance drop in 

 the line and this voltage is transferred to the compensator circuit 

 by the potential transformer T 3 . # is a reactance and consumes 



