AC Motors Construction and Operation
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Questions and Answers

What is the main advantage of AC motors over DC motors?

  • AC motors are more expensive
  • AC motors require less maintenance (correct)
  • AC motors are more efficient
  • AC motors are more powerful

    • Which of the following is a characteristic of AC synchronous motors?

  • They use brushes and commutators
  • They are single-phase motors
  • They have a variable speed
  • They have a constant speed (correct)

    • What is the primary method used to control the speed of an AC motor?

  • Using a variable resistance
  • Changing the number of poles
  • Varying the frequency (correct)
  • Adjusting the voltage

    • Which of the following describes a method for producing a rotating magnetic field in an AC motor?

    <p>Using a capacitor</p> Signup and view all the answers

    What type of AC motor is well-suited for constant-speed applications?

    <p>AC synchronous motor</p> Signup and view all the answers

    Which characteristic of AC motors eliminates the problem of dangerous sparking?

    <p>The lack of brushes and commutators</p> Signup and view all the answers

    What type of power systems are these motors designed for?

    <p>Polyphase or single-phase</p> Signup and view all the answers

    Which type of AC motors are the most commonly used?

    <p>Induction motors</p> Signup and view all the answers

    How are the rotors of synchronous motors energized?

    <p>By direct current (DC) voltage</p> Signup and view all the answers

    What is the principle behind the operation of a three-phase induction motor?

    <p>A rotating magnetic field</p> Signup and view all the answers

    How are the individual phase windings arranged in the stator of a three-phase induction motor?

    <p>They are equally spaced around the stator, 120° apart.</p> Signup and view all the answers

    Which rule is used to determine the electromagnetic polarity of the poles at any given instant in a three-phase induction motor?

    <p>The left-hand rule</p> Signup and view all the answers

    In a three-phase system, the resultant magnetic field rotates in which direction?

    <p>Clockwise</p> Signup and view all the answers

    At which point in the rotation cycle is the magnetic field in coils 1-1A at its maximum?

    <p>Point 1</p> Signup and view all the answers

    What happens when the three-phase voltage completes one full cycle?

    <p>The magnetic field rotates through 360 degrees</p> Signup and view all the answers

    At point 2, which winding experiences the maximum negative voltage?

    <p>3-3A</p> Signup and view all the answers

    What is the effect of the weaker magnetic fields in windings 1-1A and 2-2A at point 2?

    <p>They aid the magnetic field in winding 3-3A</p> Signup and view all the answers

    What is the natural alignment of a bar magnet mounted in the center of the stator?

    <p>Its south pole aligns with the north pole of the stator field</p> Signup and view all the answers

    What is the purpose of having no insulation between the core and the bars in a squirrel-cage rotor?

    <p>To allow for maximum field strength in the small air gap</p> Signup and view all the answers

    What is the other type of rotor winding mentioned in the text?

    <p>Wound rotor</p> Signup and view all the answers

    What is the basic principle of operation for an induction motor, regardless of the rotor type?

    <p>The stator field induces a magnetic field in the rotor, causing the rotor to turn</p> Signup and view all the answers

    What materials are typically used for the conducting bars in a squirrel-cage rotor?

    <p>Copper or aluminium</p> Signup and view all the answers

    How are the rotor bars connected in a squirrel-cage rotor?

    <p>They are short-circuited at each end by a solid ring</p> Signup and view all the answers

    What is the typical construction of a squirrel-cage rotor?

    <p>A laminated cylinder with slots in its surface</p> Signup and view all the answers

    What happens to the phase voltage when a motor is connected in delta configuration?

    <p>It increases by a ratio of √3</p> Signup and view all the answers

    How does the phase current change when a motor is connected in delta mode?

    <p>It increases by a ratio of √3</p> Signup and view all the answers

    What happens to the line current in a delta-connected motor compared to a star-connected motor?

    <p>It increases three times</p> Signup and view all the answers

    What is the main difference in the stator field behavior between single-phase and polyphase induction motors?

    <p>The stator field does not rotate in single-phase motors and rotates in polyphase motors</p> Signup and view all the answers

    How is voltage induced in the rotor of a single-phase induction motor?

    <p>As a result of magnetic induction</p> Signup and view all the answers

    What happens to the push-pull along the line if an outside force rotates the rotor of a single-phase motor?

    <p>It is disturbed</p> Signup and view all the answers

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