PRACTICAL OPERATION OF DYNAMOS. 



187 



a switch-board panel, and these panels, called generator panels, 

 are arranged side by side as shown in Fig. 113. The dotted 

 lines represent the panels and the full lines represent the electrical 

 connections. Fig. 1 14 shows a special form of switch for opening 

 the shunt field circuit of a generator. This switch is not shown 

 in Fig. 113, inasmuch as Fig. 113 is drawn to too small a scale. 



bus bar 



+ bus bar 



equalizing 

 bus bar 



F" 



\SLZSUiSLSU 



Fig. 113. 



G f and G" are two compound generators, F f and F" their shunt field windings, 

 R f and R" their shunt field rheostats, and C f and C" their series field windings. S / 

 and S" are two triple-pole switches, A' and A ff are ammeters, / and s" are ammeter 

 shunts, and B' and ^ /x are circuit breakers. The small dotted circles v f and v" and 

 the dotted lines show the electrical connections of the two voltmeters V and V". 



When the shunt field circuit of a dynamo is broken the current 

 persists in flowing across the break in the form of a long arc or 

 spark on account of the great electrical momentum of a current 

 in a field winding of many turns of wire. This arc, occurring 

 every time the field switch is opened, destroys the switch contacts, 

 and, what is more serious, the high electromotive force developed 



