i88 



ELEMENTS OF ELECTRICAL ENGINEERING. 



shunt Geld 



simnr 



winding 



across the break and between the terminals of the field winding is 

 likely to puncture the insulation of the winding. The arrange- 

 ment shown in Fig. 1 14 obviates these difficulties in the following 

 manner : 



The two wires p and p' connect to the armature terminals, the 

 field rheostat being placed in the field circuit at any convenient 



point. To open the shunt field 

 circuit the metal arm A is turned 

 slowly to the position A' ' . At 

 first the arm A breaks contact 

 with the metal block b and con- 

 nects the comparatively high re- 

 sistance r in series with the field 

 winding. This leaves the shunt 

 field circuit unbroken so that 

 the current can continue to flow, 

 but, on account of the high re- 

 sistance r, the current dies away 

 slowly, and by the time the arm 

 breaks contact with the metal block a, the current is already so 

 small that serious arcing across the break is obviated. 



Feeder panels. In a large lighting or power station a number 

 of separate circuits are usually supplied with current from a set 

 of parallel-connected generators. Thus Fig. 1 1 5 shows the es- 

 sential connections of three compound generators in parallel sup- 

 plying current to three circuits F, G and H. The pairs of wires 

 F y G and H are called feeders. The apparatus for controlling 

 the feeders is usually mounted upon one or more switch-board 

 panels, called feeder panels. These feeder panels are arranged 

 along side of the generator panels, and the -J- and bus bars 

 run along behind all of the panels. 



Fig. 1 1 6 shows a front, back and side elevation, and the dia- 

 gram connections of a feeder panel designed by the General 

 Electric Company for two pairs of feeders. Each feeder circuit 

 is controlled by a double-pole switch and a circuit breaker, and an 



Fig. 114. 



