Capacitor Start – Induction run Single Phase Motor

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 Capacitor Start – Induction run Single Phase Motor

  • The phase difference between main winding and starting winding is achieved by introducing an electrolyte capacitor is in series with starting winding. 
  • The capacitor is electrolyte type. When the speed of the motor is increased 70 to 80% of full load speed, the centrifugal switch open and starting winding is cut out.
    capacitor start induction run motor


    Vector diagram
    • As the capacitor is in series with starting winding, its vector IS leads supply by some angle. 
    • The current vector IM lags the supply voltage by some angle ( < 900 ) due to high inductance of the main winding. 
    • The angle between current vector IS and IM is in the range of 800 to 900 which is nearly 300 in the case of Split phase motor.

    Starting torque
    • The starting torque is directly proportional sine of angle between starting current and main current.

            T a ( Sin θ )

    • The starting torque in the capacitor start – induction run motor is about 3.5 to 4 times that of full load torque. 
    torque speed characteristic of the capacitor start induction run motor

    Advantage of Centrifugal switch over Magnetic switch
    • It is not affected by the line voltage
    • More reliable
    • Low cost 

    Electrolyte Capacitor
    • It is formed by winding two sheets of etched aluminum foil and separated by two layers of insulating layer in the shape of cylindrical.
    • This whole unit is impregnated with an electrolyte of ethylene glycol.
    • An anodic film is produced on each foil by the electro – chemical action. 
    • The voltage rating of the capacitor should not necessary be same as that of motor rating. 
    • The power factor of the such capacitor is in the range of 6 to 8 %.

    Speed Regulation
    • The speed of the motor varies 10% to 100% from no load to full load

    Rating
    • It is available in the range of 1/6 HP to 3 HP.

    Application
    • Compressors
    • Elevators
    • Conveyors 

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