150 ALTERNATING CURRENTS 



power. If the torque exerted by the engine fluctuates during each 

 revolution, it will tend to set up oscillations such as those we have 

 already considered in connection with the running of synchronous 

 motors. Any tendency towards hunting or phase-swinging may be 

 counteracted by the use of damping circuits or of sufficiently heavy 

 fly-wheels. 



In order to test the connections of the synchronizer and those of 

 the armature coils of a newly installed alternator, a good plan is to 

 couple this alternator in parallel with another which is not running, 

 and to start both machines very slowly and simultaneously. Any 

 error in the coupling of the armature circuits of the new machine will 

 cause the circuit-breakers between the machines to open, while an 

 error in the synchronizer connections will cause this instrument 

 to give wrong indications when the machines are running smoothly 

 in parallel. 



