DRIVES AND CONTROLS 217 



Capacitor motors are basically split-phase motors using split magnetic fields in 

 starting. Improved starting characteristics are obtained by using a capacitor or 

 condenser in connection with the starting winding. The electrical effect of the con- 

 denser increases the angle of the magnetic action to about 90 deg. between the two 

 windings, approaching a true two-phase effect. 



Capacitor-start and induction-run motors employ a centrifugal governor switch 

 which cuts out both the starting winding and the condenser at a predetermined speed 

 after which the motor operates as a straight single-phase squirrel-cage induction- 

 type motor. 



Capacitor-start induction-run motors wiU dehver starting torques that are 

 approximately three and one-half to four and one-half times their full load torque 

 with locked rotor currents approximately one and three-fourth times repulsion-start 

 induction-run motor currents. Their operating characteristics when running are 

 very similar to those of the repulsion start induction run type of motors. 



Capacitor-start capacitor-run motors use a capacitor and also a transformer. 

 The transformer acts to impress a high voltage on the capacitor for starting. Start- 

 ing torque is three and one-half to four and one-half times full load torque, and start- 

 ing current is of the same relative order as the capacitor-start induction-run type of 

 motor. 



Capacitor motors can be obtained for both single- and multispeed applications. 



Fractional horsepower squirrel-cage induction polyphase motors have a field 

 made up of polyphase windings and a squirrel-cage rotor made up of conductor bars. 

 The starting torque is about two and one-half to three times the full load torque. 



Squirrel-cage induction motors hke direct-current motors wUl usually pull up 

 any load they can start, i.e., the maximum pull-up torque is about equal to the starting 

 torque, and the rating of the motor should be selected to suit the greater torque as 

 required by the load. 



