ROTARY CONVERTERS 111 



and that the series fields are left open. Throw switch 

 A to the left and slowly reduce the resistance of the 

 water rheostat until it is practically short circuited, 

 when the switch 5 may be closed. The blade of the 

 water rheostat is now drawn out of the water and the 

 switch A thrown to the right. Machine No. 2 is then 

 started in a similar manner. 



The field strength of each machine is then reduced 

 until both machines run at normal speed. Next con- 

 nect a number of incandescent lamps in series, the 

 rated voltage of which is equal to the sum of the machine 

 voltage across rings A A; i.e., across switches located 

 on the dynamometer board. Two sets of lamps should 

 be provided, one being connected across one of the 

 switches while the other is stepped across each of the 

 other switches in turn. Should one set show a rise 

 and fall in voltage displaced in time with relation to 

 that of the other, the two phases are reversed and 

 must be corrected. When all phases show a simultaneous 

 rise and fall, the machines may be phased together 

 and their speeds brought to the same value by changing 

 the field on one of them. When the time between rise 

 and fall of voltage, as shown by the lamps, decreases 

 to a period of five seconds or longer, all switches are 

 closed simultaneously and the lamps become dark. 



During the period of starting and phasing the machines 

 together, the fields of the booster should be opened 

 and the armature short circuited. When the rotaries 

 are synchronized, the switches across the armatures 

 of the boosters are opened and a weak field applied, 

 the line meter on machine No. 1 being watched. The 

 reading of this meter should reverse from that given 

 on motor load, if machine No. 1 is taking load as a 

 rotary. By reversing the booster field either machine 

 can be made to run as a rotary. 



After balancing the current in each phase, full load 

 phase characteristics may be taken by holding the speed 

 constant by means of the field of the inverted machine, 

 and the load constant by means of the booster, the 

 shunt field of the rotary being varied throughout its 

 range and the current input read. Full load voltage 



