364 



ELECTRICAL EQUIPMENT 



rheostat. The rheostat is first turned in until the exciter voltage 

 is greatly reduced and the regulator circuit is then closed. This 

 short-circuits the rheostat through contacts in the regulator and 

 the voltage of the exciter and generator immediately rises. At a 

 predetermined point the regulator contacts are automatically 

 opened and the field current of the exciter must again pass through 

 the rheostat. The resulting reduction in voltage is arrested at 

 once by the closing of the regulator contacts which continue to 

 vibrate in this manner and keep the generator voltage within the 

 desired limits. 



Method of Operation. An elementary diagram of the type 

 T.A. regulator connections with an alternating-current generator 

 and exciter is shown in Fig. 218. The regulator has a direct- 



Main Contacts 



FIG. 218. Elementary Connections of Type T.A. Automatic Voltage 



Regulator. 



current control magnet, an alternating-current control magnet, 

 and a relay. The direct-current control magnet is connected to 

 the exciter bus-bars. This magnet has a fixed stop-core in the 

 bottom and a movable core in the top which is attached to a piv- 

 oted lever having at the opposite end a flexible contact pulled 

 downward by four spiral springs. For clearness, however, only 

 one spring is shown in the diagram. Opposite the direct-current 

 control magnet is the alternating-current which has a potential 

 winding connected by means of a potential transformer to the alter- 

 nating-current generator or bus-bars. There is an adjustable com- 



