Machines; Single Phase Motors Flashcards
Between single phase and three phase, which performs better?
3 phase
What hp are most single phase motors?
Fractional (1/6 to 3/4 hp)
Typical efficiency ratings of single phase motors?
60%
Newer energy efficient models can reach ____ % efficiency
68
What type of technology has made significant improvements to single phase motor design?
Written-pole
How many sets of stator windings are commonly found in single phase induction motors?
2
What produces the rotating magnetic field required to start the motor from one single-phase voltage?
Current in one stator winding is caused to be out-of-phase with the other
How are split phase motors classified?
By the way the two stator windings are used to start and run the motor.
What are the 4 classifications of split phase motors?
1) resistance split phase motor
2) capacitor-start motor
3) permanent-split capacitor motor
4) two-value capacitor motor (ie. Capacitor start capacitor run motor)
How does a resistance split-phase motor create a phase angle between the two currents in the stator?
Uses windings with different values of resistance and inductance
What are the basic components of a resistance split-phase motor?
Stator, frame, rotor, centrifugal switch
What are the run windings?
Also called main windings, are large insulated copper conductors mounted in the bottom of the stator slots.
What are start windings of a resistance split-phase motor?
Also called auxiliary winding, made of smaller conductors with fewer turns placed on top of the stator slots
Positioning of start windings and main windings on a two-pole vs. 4-pole motor.
2 pole = center of start @ 90° from the main
4 pole = 45°
What type of rotor is used in a resistance split phase motor?
Squirrel cage type
What are most squirrel cages made of?
Cast aluminum
Where is a fan mounted for cooling a resistance split phase motor?
Rotor
What is a centrifugal switch used for?
Disconnecting the start winding when the motor reaches full load speed
What components make up a centrifugal switch?
Stationary component (N/C contact) on end bell Rotating component on rotor
How is the switch of a centrifugal switch actuated?
By centrifugal force produced by the spinning rotor
When does the centrifugal switch contact open?
75% of the rated speed of the motor
How is the contact of a centrifugal switch connected?
Series with start winding
What other methods (besides centrifugal switch) are available to cut out the start winding?
Current sensitive relay
Electronic switching devices (triacs)
What type of start winding cut-out does not have contacts and can be located some distance from the motor?
Triacs with solid state controls
