VOLTAGE REGULATION 



365 



pensatmg winding on the alternating-current magnet connected 

 through a current transformer to the principal lighting feeder. The 

 object of this winding is to raise the 

 voltage of the alternating-current 

 bus-bars as the load increases. The 

 alternating current control magnet 

 has a movable core and a lever and 

 contacts similar to those of the direct- 

 current control magnet, and the two 

 combined produce what is known 

 as the " floating main contacts." 



The number of relays vary ac- 

 cording to the number and size of 

 the exciters, and while the funda- 

 mental principle of operation of all 

 the forms of T.A. regulators is the 

 same, certain modifications are 

 necessary. The relay consists of a 

 U-shaped magnet core having a 

 differential winding and a pivoted 

 armature controlling the contacts 

 which open and close the shunt cir- 

 cuit across the exciter field rheostat. 

 One of the differential windings of 

 the relay is permanently connected 

 across the exciter bus-bars and tends 

 to keep the contacts open ; the other 

 winding is connected to the exciter 

 bus-bars through the floating main 

 contacts and when the latter are 

 closed neutralizes the effect of the 

 first winding and allows the relay 

 contacts to short-circuit the exciter 

 field rheostat. Condensers are con- 

 nected across the relay contacts to 

 prevent severe arcing and possible 

 injury. 



The regulator may be mounted on the switchboard or on pedes- 

 tals, as in Fig. 219, this particular form having twenty relays, 

 divided into two groups. 



FIG. 219. Type T.A. Automatic 

 Voltage Regulator Mounted 

 on Pedestal. 



