ELECTRIC DISTRIBUTION AND WIRING. 



271 



and the distances between these inclined lines at the ends of 

 the mains represent the voltages acting on the two sets of lamps. 

 Thus the voltage b acting on the A -set is 1 1 5 volts 5 volts j 

 volt = 109.5 volts., and the voltage ^acting on the JB-set is 115 

 volts 4^ volts -f Y* volt = in volts. 



113. Special three-wire generators and three-wire balancers. 



The use of two generators as indicated in Figs. 156 and 157 

 involves an added expense for machinery in the generating 

 station, and the extensive use of the Edison three-wire system 

 has given rise to several special types of three-wire generators 

 which can be used singly for supplying a three -wire system, and 

 to several types of an auxiliary device, called a three-wire balancer , 

 which enables a single 22O-volt generator of the ordinary type to 

 supply an Edison three-wire system. 



(a) The split-pole three -wire generator. Fig. 1 5 8# shows a 

 two-pole 22O-volt generator with each pole, NN' and SS f , sepa- 



Fig. 158. 



rated into two parts by deep slots, pp. The main brushes, a and 



b, collect current at 220 volts, an auxiliary brush, c, makes contact 

 with the commutator midway between a and b t and the middle 

 main of the three-wire system is connected to this auxiliary brush, 



c. The auxiliary brush, c t cannot be used on an ordinary solid 

 pole generator because the sections of the armature winding as 



