Electrical Machines: D.C. Machine as a Generator
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Questions and Answers

What principle do all generators work on?

  • Ohm's law
  • Coulomb's law
  • Faraday's law of electromagnetic induction (correct)
  • Newton's law of universal gravitation
  • What determines the magnitude of the induced e.m.f in a conductor?

  • Conductor's resistance
  • Conductor's length
  • Conductor's temperature
  • Rate of change of flux associated with the conductor (correct)
  • What is the relative motion required to induce an e.m.f in a conductor?

  • Increasing the number of conductors in the winding
  • Changing the physical dimensions of the winding
  • Applying a voltage to the conductor
  • Rotating conductor with respect to flux or rotating flux with respect to a conductor (correct)
  • What is the winding formed by connecting a number of conductors together called?

    <p>Armature winding</p> Signup and view all the answers

    What part of a D.C. machine is the armature winding kept on?

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

    What is the function of the yoke in a DC machine?

    <p>To protect insulating materials from atmospheric elements</p> Signup and view all the answers

    Why is cast iron chosen for making the yoke in a DC machine?

    <p>It is the cheapest material available</p> Signup and view all the answers

    What is the function of the pole shoe in a DC machine?

    <p>To enlarge the area of armature core to come across the flux</p> Signup and view all the answers

    Why is a laminated construction used for making the poles in a DC machine?

    <p>It requires a definite shape and size</p> Signup and view all the answers

    What is the role of the field winding in a DC machine?

    <p>To produce the magnetic flux</p> Signup and view all the answers

    Study Notes

    Principles of Generators

    • Generators operate on the principle of electromagnetic induction, where a change in magnetic field induces an electromotive force (e.m.f) in a conductor.

    Induced e.m.f Magnitude

    • The magnitude of the induced e.m.f in a conductor is determined by the rate of change of magnetic flux through the conductor, the strength of the magnetic field, and the number of turns in the coil.

    Relative Motion for Inducing e.m.f

    • Relative motion between a magnetic field and a conductor is required to induce an e.m.f. This can occur through either the movement of the conductor within a magnetic field or the movement of the magnetic field around the conductor.

    Winding in Generators

    • The winding formed by connecting a number of conductors together is known as a coil.

    Armature Winding in D.C. Machines

    • In a D.C. machine, the armature winding is typically kept on the rotor, which is the rotating part of the machine.

    Function of the Yoke in D.C. Machines

    • The yoke provides mechanical support for the internal parts of the D.C. machine and acts as a protective enclosure. It also connects the poles, ensuring magnetic continuity.

    Material Choice for Yoke

    • Cast iron is chosen for making the yoke in D.C. machines due to its strength, durability, and magnetic properties, which help in reducing magnetic losses.

    Function of the Pole Shoe

    • The pole shoe in a D.C. machine serves to spread the magnetic flux over a larger area of the armature, ensuring more efficient magnetic coupling and minimizing saturation effects.

    Laminated Poles in D.C. Machines

    • Laminated construction is used for making the poles in a D.C. machine to reduce eddy current losses. By laminating the material, the path for the currents is broken up, diminishing energy wastage.

    Role of Field Winding

    • The field winding in a D.C. machine generates the magnetic field necessary for operation. It can be arranged in series or parallel configurations with respect to the armature to affect the machine’s performance characteristics.

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    Description

    Explore the principle of dynamically induced e.m.f in D.C. machines and how generators work based on Faraday's law of electromagnetic induction. Learn about the magnitude of the induced e.m.f in a conductor.

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