SWITCHBOARDS AND SWITCHBOARD APPLIANCES. 341 



circuit through the ground detector, by inserting a condenser 

 between A and C and another between B and D in Fig. 293, 

 which represents the diagram of connections of the Westing- 

 house ground detector. 



154, Oil switches. Figures 295 

 and 296 show front and rear views 

 of an automatic oil switch (circuit- 

 breaker) of the Westinghouse 

 Electric and Manufacturing Com- 

 pany. Figure 295 shows the trip- 

 ping magnet which releases the 

 lever of the switch and causes the 

 switch to open, and Fig. 296 shows 

 the essential parts of the switch. 

 This particular switch is a three- 

 phase single-pole switch, that is to 

 say, it is three separate single-pole 

 switches, one for each phase of a 

 three-phase system, and each switch 

 breaks under oil. One of the oil 

 vessels is shown removed in Fig. 296. 



155. The Tirrill regulator. The essential features of the 

 Tirrill regulator as constructed by the General Electric Company 

 are shown in Fig. 297. 



The contact C short circuits the field rheostat of the exciter ; 

 when the contact C is closed the exciter voltage rises, the cur- 

 rent in the field winding of the main generator grows, and the 

 voltage of the main generator tends to increase. 



The relay R, with a differential winding A and B, actuates 

 the contact C. When the points T and T f are not in contact, 

 current flows through coil A only, the relay is excited, and the 

 contact C is opened ; when the points T and T' are in con- 

 tact, the current which flows through coil B neutralizes the 

 magnetizing action of coil A, the relay is not excited, and the 

 contact C is closed. 



B Oil Circuit-breaker. 

 (Switchboard Mounting Front View) 

 Fig. 295. 



