AC Machines: Synchronous vs. Induction
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Questions and Answers

What is the principal difference between synchronous machines and induction machines?

  • Synchronous machines require a dc field current to be supplied to their rotors, while induction machines have the field current induced in their rotors by transformer action. (correct)
  • Synchronous machines and induction machines both have the field current induced in their rotors by transformer action.
  • Synchronous machines have the field current induced in their rotors by transformer action, while induction machines require a dc field current to be supplied to their rotors.
  • Synchronous machines and induction machines both require a dc field current to be supplied to their rotors.

    • What produces a uniform rotating magnetic field within the stator of a three-phase system of currents?

  • The electrical frequency of the stator
  • The direction of rotation of the magnetic field
  • The mechanical rotation of the magnetic fields
  • A system of three coils spaced 120 electrical degrees apart (correct)

    • How can the direction of rotation of the magnetic field be reversed in a three-phase system?

  • By altering the number of poles in the stator
  • By changing the electrical frequency of the stator
  • By increasing the mechanical rate of rotation of the magnetic fields
  • By simply swapping the connections to any two of the three phases (correct)

    • What types of losses occur in ac machines?

    <p>Electrical or copper losses (I2R losses), core losses, mechanical losses, and stray losses</p> Signup and view all the answers

    How is the electrical angle of the voltages and currents related to the mechanical angle of the magnetic fields in a stator with more than two poles?

    <p>One mechanical rotation produces P/2 electrical cycles</p> Signup and view all the answers

    What is the principal difference between synchronous machines and induction machines?

    <p>Synchronous machines require a dc field current, while induction machines have the field current induced by transformer action</p> Signup and view all the answers

    What produces a uniform rotating magnetic field within the stator of a three-phase system of currents?

    <p>A system of three coils spaced 120 electrical degrees apart on a stator</p> Signup and view all the answers

    How can the direction of rotation of the magnetic field be reversed in a three-phase system?

    <p>By simply swapping the connections to any two of the three phases</p> Signup and view all the answers

    What types of losses occur in ac machines?

    <p>Electrical or copper losses (I2R losses), core losses, mechanical losses, and stray losses</p> Signup and view all the answers

    Study Notes

    Synchronous Machines vs. Induction Machines

    • Principal difference: Synchronous machines rotate at a constant speed, whereas induction machines rotate at a speed dependent on the slip between the rotor and the rotating magnetic field.

    Rotating Magnetic Field

    • Uniform rotating magnetic field is produced by a three-phase system of currents in the stator.
    • Reversing the direction of rotation of the magnetic field can be done by changing the phase sequence of the currents.

    Losses in AC Machines

    • Types of losses: Copper losses, Iron losses, Mechanical losses, and Stray losses.

    Electrical Angle vs. Mechanical Angle

    • In a stator with more than two poles, the electrical angle of the voltages and currents is related to the mechanical angle of the magnetic fields by a factor of pole pairs.

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    Description

    Explore the key differences between synchronous machines, which require a DC field current, and induction machines, which have the field current induced by transformer action. Learn about three-phase systems and stator coils in detail.

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