Electric Machines Speed-Torque Characteristics
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Questions and Answers

In which type of load is the load torque proportional to the square of the speed?

  • Machines tools and piston pumps
  • Eddy current brakes
  • Cranes and hoists
  • Fans and rotary pumps (correct)
  • What type of speed-torque characteristics are exhibited by certain types of lathes, boring machines, and steel mill coilers?

  • Hyperbolic speed-torque characteristics (correct)
  • Constant torque characteristics
  • Linear rising characteristics
  • Non-linear falling characteristics
  • For separately excited DC generators connected to a constant resistance load, what are the speed torque characteristics?

  • Non-linear falling characteristics
  • Linear rising characteristics (correct)
  • Non-linear rising characteristics
  • Constant torque characteristics
  • What does the speed/torque characteristic equation T = To + (TR - TO) / (nr)^(x) help determine?

    <p>The relationship between motor speed and load torque</p> Signup and view all the answers

    In the context of the speed/torque characteristics, what does it mean if x = 0 in the equation T = To + (TR - TO) / (nr)^(x)?

    <p>The load torque remains constant regardless of speed</p> Signup and view all the answers

    What does the exponential factor 'x' in the speed/torque characteristic equation represent?

    <p>The change in the resisting torque with change in speed</p> Signup and view all the answers

    What happens to the armature during dynamic braking of a compound motor?

    <p>It is disconnected from the supply and connected across the braking resistor</p> Signup and view all the answers

    How does the magnetizing force of the series field winding vary in the counter current braking of a compound motor?

    <p>It varies linearly with armature current</p> Signup and view all the answers

    What happens to the speed torque characteristics during regenerative braking of a compound motor?

    <p>It forms a straight line</p> Signup and view all the answers

    Why is the series field winding of a compound motor connected like a shunt motor during regenerative braking?

    <p>To avoid demagnetization of the motor</p> Signup and view all the answers

    Study Notes

    Load Torque Characteristics

    • Load torque is proportional to the square of the speed in a quadratic load.

    Speed-Torque Characteristics

    • Certain types of lathes, boring machines, and steel mill coilers exhibit a quadratic speed-torque characteristic.

    Separately Excited DC Generators

    • Separately excited DC generators connected to a constant resistance load have a linear speed-torque characteristic.

    Speed-Torque Characteristic Equation

    • The equation T = To + (TR - TO) / (nr)^(x) helps determine the speed-torque characteristic of a motor.
    • If x = 0 in the equation, it means the speed-torque characteristic is linear.
    • The exponential factor 'x' in the speed-torque characteristic equation represents the type of load.

    Compound Motor Braking

    • During dynamic braking of a compound motor, the armature acts as a generator.
    • During counter-current braking of a compound motor, the magnetizing force of the series field winding varies inversely with the speed.
    • During regenerative braking of a compound motor, the speed-torque characteristic becomes linear.
    • The series field winding of a compound motor is connected like a shunt motor during regenerative braking to achieve a linear speed-torque characteristic.

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    Description

    Explore the study of speed/torque characteristics of electric motors and their suitability for driving industrial equipment. Learn about the variation of load torque with the speed of the driven machine and the different types of loads' speed-torque characteristics.

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