Single Phase AC Motors Flashcards
How is the rotating magnetic field developed in a split phase motor?
Single phase AC supply feeding two parallel connected windings (run & start) resulting in two currents ideally phase displaced by 90°
Physical characteristics of the “start” & “run” windings?
Start = Smaller wire, higher resistance, lots of turns, closer to outside of stator
Run = Larger wire, low resistance, fewer turns, deep in stator
At what speed does the centrifucal switch disconnect the start winding from the line? Why does it do this?
75% of synchronous speed. Starting winding is not rated for continuous duty
How do you reverse the direction of rotation for a single phase AC motor?
interchange start OR run leads
start is standard
What would happen to a capacitor start motor if the centrifugal contacts welded closed during start?
Slower speed/burnout
What would happen to a capacitor start motor if the centrifugal contacts remained open during starting?
No start / high current
What advantages are gained from a “permanent capacitor” single phase induction motor?
Quiet running speed / good operating PF
What is another name commonly applied to the AC series motor?
Universal Motor
What are some common applications of of a single phase AC series motor?
Drills, Vacuums, Reciprocating Saws
How would you reverse the direction of rotation for an AC series motor?
Interchange armature leads
Describe constructional features of a shaded pole AC motor stator
Shading coils placed on one side of wound stator poles
Describe constructional features of a shaded pole AC motor rotor
Regular squirrel cage rotor (high resistance)
How could you reverse the direction of rotation for a shaded pole type AC motor?
Change the orientation of the stator
How is a single phase AC synchronous motor constructed?
Shading coil type stator with hardened steel rotor
what is the main difference between the performance between a split phase induction motor and a capacitor start induction motor?
Capacitor start has a greater starting torque
What is the main function of the capacitor in the capacitor start induction motor?
Improve the starting torque
List two methods of controlling the speed on a single phase universal motor?
- Series resistor
2. Electronic control
what is the main advantage of a universal single phase motor?
High starting torque
which single phase motor has the best speed regulation?
Synchronous motor
which motor has the worst speed regulation from no load to full load?
Universal motor
What are two advantages and disadvantages of Shaded pole motors?
Advantages: Cheap & simple
Disadvantages: Poor torque, inefficient
Name two applications of shaded pole motors
Bathroom fans, small appliances
Main parts of single phase AC motors?
- Stator
- main/run winding
- aux/start winding - Rotor
- squirrel cage - Centrifugal switch
- End bells/bearings
- Nameplate
What are the 4 main types of single phase motors?
- Resistive start / Induction run
- Capacitor Start
- Capacitor start / capacitor run
- Capacitor Run
Which winding current is more out of phase of the voltage in a resistive start / induction run motor? what is the typical angle between the two winding currents?
Run current lags the supply voltage more than the start.
Run & start are typically 30-50° phase displaced
