SYNCHRONOUS MOTORS. 



269 



may be made to start by running the alternator very slowly, and 

 then giving the motor a few sharp turns by hand to bring it to 

 the reduced speed of the alternator. In starting the motor 

 in this way it will be found easiest to turn the motor by hand 

 without excitation, and to switch on the field when sufficient 

 speed is attained for it to fall into step with the alternator. 

 If the alternator speed is then gradually increased, the motor 

 will speed up and keep in step. 



If a synchronous alternating-current motor is to be con- 

 nected to an alternating circuit, it must first be run up to 

 the speed of synchronism, its field must be adjusted to the 

 correct amount, and the switch connecting it to the supply 

 must be closed when the phase of the motor corresponds to 

 that of the circuit. 



The process is consequently similar to that adopted in 

 synchronising two alternators (see page 259). 



The following experiment is suggested specially as being 

 suitable for giving practice in the starting of synchronous 

 motors. 



EXPERIMENT XLI. To START A SYNCHRONOUS MOTOR 

 AND ASCERTAIN THE LlMITS OF EXCITATION FOR WHICH IT 

 WILL START. 



DIAGRAM OF CONNECTIONS. 



FIG. 128. 



Source of alternating current. 



Source of direct current. 

 M Motor armature. 



F Motor field windings. 



A { Ammeter reading armature current. 



A 2 Ammeter reading exciting current, 



V Voltmeter, 



