256 



ELECTRICAL MACHINERY 



alternator field current as the load is increased and decreased 

 or else to have some automatic device to regulate the alter- 

 nator field. 



Operation of the Voltage (or Tirrill) Regulator. The 

 Tirrill regulator (so named after its inventor) serves the 

 purpose by controlling a resistance in the field of the 

 exciter furnishing the alternator field current. A cut 

 showing this ingenious device is given in Fig. 156 and 



FIG. 156. View of Voltage Regulator (Tin-ill Regulator) General 



Electric Co. 



a diagram of its connections is given in Fig. 157 by 

 reference to which its action will be described. A diagram 

 of the exciter with its field rheostat and its connection to 

 the alternator is given to make the operation of the regulator 

 easier to understand. 



Essentially the regulator consists of three magnets, 

 A, A', and F and two pairs of contacts C, C' and E, E f , 

 which are opened and closed by these magnets. 



Differential Relay Magnet. The operation of the differ- 

 ential relay magnet F will first be described. Its winding 



