108 COMMERCIAL ELECTRICAL TESTING 



mometer boards and to the alternating current rings of 

 the machine are of the same length and capacity, and 

 that all .contacts are cleaned and brightened before 

 connection. Equal resistance per phase will thus be 

 obtained and unbalancing in the alternating current 

 circuits external to the armature prevented. In wiring 

 the direct current circuit, the series field and its shunt 

 are disconnected. 



When wiring rotaries, as in the case of all other 

 high current direct current machines, both sides of 

 the circuit should be laid close together. No iron, 

 such as a bearing pedestal or a section of the frame, 

 must lie within the loop of the circuit, since it will 

 become magnetized and materially affect the operation 

 of the machine and instruments. Divide the shunt 

 field into at least four sections by a "break up switch," 

 which must always be open while starting from the 

 alternating current end; since, due to transformer 

 action and the relative number of turns of the field 

 and armature, a high voltage is induced in the field 

 at starting. 



Always wire the positive ring of the rotary through 

 a breaker to the blade of the water box, and the negative 

 ring to the box itself. Connect enough boxes in multiple 

 to limit the current per box to about 400 amperes 

 maximum. Make provision for reading alternating 

 current amperes and volts armature, direct current 

 amperes and volts armature, amperes and volts field, 

 and the speed of the alternator. 



To start the machine, close the alternating current 

 line switches, and the field switch of the driving alter- 

 nator, increasing the excitation of the alternator and 

 keeping close watch on the current in the alternating 

 current lines. If this current reaches 150 per cent 

 normal before the rotary starts, check over the wiring. 

 If the machine starts rotating in the wrong direction, 

 reverse two of the leads on the primary side of the 

 transformers. After starting, as soon as the alternating 

 current drops to the minimum value (showing that 

 the machine is in synchronism), and the alternating 

 current volts become normal, close the field "break 



