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ELECTRICAL MACHINERY 



carry much current, there is an additional winding at right 

 angles to this, which is designed of sufficient size to carry 

 a magnetizing current during the starting period only. 

 After the rotor approaches synchronous speed this additional 

 winding is automatically cut out of the circuit. Fig. 

 226 shows the connection for such a split-phase motor; the 

 auxiliary coil is connected to the single-phase supply line 

 through a condenser. This condenser, if large enough, will 

 make the current in the auxiliary coil lead the current in 

 the main coil by nearly 90, hence the two coils act like the 

 two coils of a two-phase motor and produce a rotating 



Main Coil 



FIG. 226. Connection for a Split-phase, Single-phase Induction 

 Motor, using Condenser to Get the Out-of-phase Current in the 

 Starting Coil. 



magnetic field. After a suitable speed has been reached, 

 the auxiliary circuit is opened to prevent overheating. 

 An inductance may be used instead of a condenser to bring 

 about the phase difference of the currents in the two 

 windings. 



Commutator Type of Motor. Another type of single- 

 phase induction motor which is much used employs a rotor 

 fitted with a commutator and brushes quite similar to a 

 continuous-current motor. After the motor reaches the 

 proper speed, all of the commutator bars are automatically 

 short-circuited and the brushes lifted from the commutator. 

 This action changes the rotor to an ordinary squirrel-cage 



