Capacitor-Start Motor Characteristics
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Questions and Answers

What determines the direction of rotation in a reluctance-start motor?

  • The narrow air gap
  • The pole flux components
  • The wide air gap (correct)
  • The direction of the AC source

    • Why does a reluctance-start motor develop starting torque?

  • Due to the single-phase AC source
  • Because the pole flux has two in-phase components
  • Because the pole flux has two out-of-phase components (correct)
  • Due to the difference in air gaps

    • What is a characteristic of reluctance-start motors?

  • They are made in large sizes
  • They have high starting and overload torque requirements
  • They are made in small sizes only (correct)
  • They can be reversed

    • How is speed control accomplished in a reluctance-start motor?

    <p>By varying the voltage across the motor</p> Signup and view all the answers

    What type of machine is a split-phase motor?

    <p>An induction machine</p> Signup and view all the answers

    What is a characteristic of split-phase motors?

    <p>They are made in larger ratings than shaded-pole and reluctance-start motors</p> Signup and view all the answers

    What is a characteristic of the flux in a magnetic circuit containing no iron?

    <p>It is in phase with the exciting current</p> Signup and view all the answers

    What happens to the flux when the mmf of a coil produces flux in a magnetic circuit made entirely of iron?

    <p>It lags behind the exciting current</p> Signup and view all the answers

    What is the main difference between a capacitor-start motor and a standard split-phase motor?

    <p>The capacitor-start motor develops more starting torque with a lower inrush current during the starting period.</p> Signup and view all the answers

    What is the primary application of a capacitor-start split-phase motor?

    <p>Small portable hoist applications</p> Signup and view all the answers

    What is the main advantage of a two-value capacitor motor?

    <p>It retains the benefits of a capacitor during both normal running and starting periods.</p> Signup and view all the answers

    What is the typical starting torque of a single-value capacitor motor?

    <p>Between 50 to 100 percent of rated torque</p> Signup and view all the answers

    What is the main characteristic of a single-value capacitor motor that makes it suitable for applications requiring frequent back-and-forth movement?

    <p>Ease of reversing by simply swapping the two identical windings</p> Signup and view all the answers

    What type of capacitor is used in a two-value capacitor motor?

    <p>A single capacitor unit with a transformed value</p> Signup and view all the answers

    What is the primary advantage of a capacitor-start motor over a reluctance-start motor?

    <p>Higher starting torque</p> Signup and view all the answers

    What type of applications are single-value capacitor motors commonly used in?

    <p>Air-moving equipment like fans and blowers</p> Signup and view all the answers

    What is the primary function of a centrifugal device in a split-phase motor?

    <p>To disconnect the auxiliary winding at the proper time</p> Signup and view all the answers

    What is the typical current inrush when starting a split-phase motor directly from the line?

    <p>4 to 6 times the rated value</p> Signup and view all the answers

    What is the purpose of the capacitor in a capacitor-start motor?

    <p>To make the auxiliary and main winding starting currents more out of phase</p> Signup and view all the answers

    What is the typical application of standard split-phase motors?

    <p>Applications requiring low starting torques and brief starting periods</p> Signup and view all the answers

    What is the effectiveness of speed control in split-phase motors?

    <p>It is difficult and requires special windings to change the speed</p> Signup and view all the answers

    What is the primary advantage of using a capacitor in a capacitor-start motor?

    <p>It overcomes the lack of sufficient starting torque</p> Signup and view all the answers

    What is the speed variation of split-phase motors between no load and full load?

    <p>About 2.5 to 5 percent</p> Signup and view all the answers

    What is the key factor in determining the direction of rotation in a split-phase motor?

    <p>The connection of the main and auxiliary windings to the source and with respect to each other</p> Signup and view all the answers

    Study Notes

    Capacitor-Start Motor

    • Develops more starting torque with a lower inrush current compared to standard split-phase motor
    • Suitable for small portable hoist applications, requiring a control circuit for instant reversal of direction

    Two-Value Capacitor Motor

    • Uses an autotransformer and a single capacitor unit
    • Appears to the primary as having a value of (a²)C, where 'a' is the transformation ratio
    • Retains benefits of a capacitor during both normal running and starting periods

    Single-Value Capacitor Motor

    • Has a permanently connected capacitor in the auxiliary winding circuit
    • Frequently used in air-moving equipment like fans and blowers, or in applications requiring quiet operation
    • Starting torque between 50 to 100 percent of rated torque
    • Ease of reversing by simply swapping the two identical windings

    Reluctance-Start Motor

    • Direction of rotation is always from the wide air gap to the narrow air gap
    • Starting torque is developed due to two out-of-phase components of flux
    • Not as widely used as shaded-pole motors, made in small sizes only, and applied where starting and overload torque requirements are low
    • Cannot be reversed and must be assembled so that the rotor shaft extends from the motor to drive the load in the proper direction
    • Speed control is accomplished by varying the voltage across the motor

    Split-Phase Motor

    • One of the most widely used types of single-phase motor
    • Fundamentally an induction machine, as the rotor power is received inductively
    • Mechanism actuated by a centrifugal device or an electromagnetic relay is used to cut out the auxiliary winding at the proper time
    • Direction of rotation is determined by the connection of the main and auxiliary windings to the source and with respect to each other
    • Starting current inrush may be 4 to 6 times the rated value
    • Speed control is difficult and requires special windings to change the speed
    • Speed regulation is similar to polyphase motors, with a speed variation of about 2.5 to 5 percent between no load and full load

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    Description

    This quiz covers the characteristics and applications of capacitor-start motors, including their starting torque and operating characteristics.

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