Single-Phase Induction Motor
40 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the purpose of making the stator flux rotating type in a single-phase induction motor?

  • To increase the motor's speed
  • To make the motor self-starting (correct)
  • To decrease the motor's torque
  • To reduce the motor's efficiency

    • Why does a single-phase induction motor require some starting means?

  • Because the alternating flux cannot produce rotation in a stationary squirrel-cage rotor (correct)
  • Because the motor is not self-sustaining
  • Because the stator windings produce a rotating magnetic field
  • Because the rotor is not laminated

    • What is the main problem with the pulsating flux produced by the main winding?

  • It is too weak
  • It is alternating and does not rotate (correct)
  • It is rotating in both directions
  • It is too strong

    • What happens if the rotor of a single-phase I.M is rotated in one direction by some mechanical means?

    <p>The rotor quickly accelerates until it reaches a speed slightly below the synchronous speed</p> Signup and view all the answers

    What is the direction of rotation of the motor due to the forward rotating field?

    <p>Forward direction</p> Signup and view all the answers

    What is the percentage of positive slip generated by the forward rotating field?

    <p>1-3%</p> Signup and view all the answers

    What is the purpose of the aluminum bars in the squirrel cage rotor?

    <p>To short-circuit the slots at both ends with a ring</p> Signup and view all the answers

    What is the reason for a single-phase induction motor not being self-starting?

    <p>The magnetic field produced is pulsating but not rotating</p> Signup and view all the answers

    What is the formula to calculate the slip (Sp) in a single-phase induction motor?

    <p>(Ns - Nr)/Ns</p> Signup and view all the answers

    What is the percentage of negative slip generated by the reverse rotating field?

    <p>1.95%</p> Signup and view all the answers

    What is the basis of the behavior of a single-phase induction motor?

    <p>Double-revolving field theory</p> Signup and view all the answers

    What is the characteristic of a single-phase induction motor when connected to a single-phase a.c. supply?

    <p>It does not develop any starting torque</p> Signup and view all the answers

    What is the formula to calculate the negative slip (Sneg) in a single-phase induction motor?

    <p>(Ns + Nr)/Ns</p> Signup and view all the answers

    What is the theory used to describe the operation of a single-phase induction motor?

    <p>Double Revolving Field Theory</p> Signup and view all the answers

    What is the consequence of rotating the rotor of a single-phase I.M by some mechanical means?

    <p>The motor will start and continue to rotate even though single-phase current is flowing through the stator winding</p> Signup and view all the answers

    Why is this method of starting not convenient for large motors?

    <p>Because it requires some mechanical means</p> Signup and view all the answers

    What is the range of small positive slip that generates larger torque than a large negative slip?

    <p>0.01-0.03</p> Signup and view all the answers

    What is the purpose of the auxiliary winding in a single-phase IM?

    <p>To shift the EMF and aid in starting</p> Signup and view all the answers

    What happens to the auxiliary winding when the rotor reaches synchronous speed?

    <p>It is disconnected from the supply</p> Signup and view all the answers

    According to the Double Revolving Field Theory, what is the magnitude of each rotating component?

    <p>One-half of the maximum stator flux</p> Signup and view all the answers

    What is the direction of rotation of the forward component of the stator flux?

    <p>Anti-clockwise</p> Signup and view all the answers

    What is the relationship between the synchronous speed and the supply frequency?

    <p>The synchronous speed is directly proportional to the supply frequency</p> Signup and view all the answers

    What is the resultant of the two components Φf and Φb at start?

    <p>ΦR = 0</p> Signup and view all the answers

    Why are single-phase induction motors not self-starting according to double revolving field theory?

    <p>Because the two torque components are equal in magnitude, but opposite in direction</p> Signup and view all the answers

    What is the effect of the rotating field on the rotor, according to the Double Revolving Field Theory?

    <p>The torque due to the rotating field is more in the direction of initial rotation</p> Signup and view all the answers

    What is the resultant of the two rotating components of the stator flux at any instant?

    <p>The instantaneous value of the stator flux</p> Signup and view all the answers

    What happens to the two components Φf and Φb after 90°?

    <p>They point in the same direction</p> Signup and view all the answers

    What is the direction of the torque produced by the interaction of the rotor flux with the forward component Φf?

    <p>Anti-clockwise direction</p> Signup and view all the answers

    What is the instantaneous value of the stator flux at θ = 90°?

    <p>ΦR = Φ1m</p> Signup and view all the answers

    What is the effect of the rotor flux interacting with the backward component Φb?

    <p>Produces a torque in the clockwise direction</p> Signup and view all the answers

    What is the net torque experienced by the rotor at starting?

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

    What can be used to show the two oppositely directed torques and the resultant torque?

    <p>Torque-speed characteristics</p> Signup and view all the answers

    According to the double-field revolving theory, how many constant-amplitude fluxes are produced in a single-phase induction motor?

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

    What is the relationship between the equivalent circuits of the two motors in a single-phase induction motor?

    <p>They are connected in series</p> Signup and view all the answers

    What is the input power equation for a single-phase induction motor?

    <p>Pin = Is * Vs * p.f</p> Signup and view all the answers

    What is the significance of the double-field revolving theory in understanding single-phase induction motors?

    <p>It explains the production of pulsating flux in single-phase induction motors</p> Signup and view all the answers

    What is the relationship between the rotor values in the equivalent circuit of a single-phase induction motor?

    <p>The rotor resistance and reactance are half the actual values</p> Signup and view all the answers

    What is the condition for a single-phase induction motor to operate in the running condition?

    <p>Ef &gt;&gt; Eb</p> Signup and view all the answers

    What is the purpose of the capacitor in a single-phase induction motor?

    <p>To provide a starting torque</p> Signup and view all the answers

    What is an advantage of single-phase induction motors?

    <p>Simple and robust construction</p> Signup and view all the answers

    Study Notes

    Single-Phase Induction Motor

    • A single-phase induction motor is not self-starting, unlike a three-phase induction motor, and requires some starting means such as electric or electronic means.
    • The single-phase stator windings produce a magnetic field that pulsates in strength in a sinusoidal manner, which does not rotate and therefore cannot produce rotation in a stationary squirrel-cage rotor.

    Squirrel Cage Rotor

    • The rotor has a laminated iron core with slots, and aluminum bars are molded on the slots and short-circuited at both ends with a ring.
    • The rotor quickly accelerates until it reaches a speed slightly below the synchronous speed once it is rotated in one direction by some mechanical means.

    Basics of Single-Phase Induction Motor

    • A single-phase induction motor inherently does not develop any starting torque and therefore will not start to rotate if the stator winding is connected to a single-phase ac supply.
    • However, if the rotor is started by auxiliary means, the motor will quickly attain the rated speed.

    Double Revolving Field Theory

    • The pulsating flux produced by the main winding can be resolved into two counter-rotating components (forward and backward components).
    • The motor can be started in the direction of the forward rotating field, which generates a small (≈1-3%) positive slip.
    • The reverse rotating field generates a larger (≈1.95%) negative slip.
    • The interaction between the fields and the current induced in the rotor bars generates opposing torque.

    Solution to Starting Torque Problem

    • The single-phase induction motor can be made self-starting by adding an auxiliary winding in the slots of the stator to shift the EMF.
    • The auxiliary winding and main winding are connected in parallel together and with the supply.
    • When the rotor moves with speed until the synchronous speed, the auxiliary winding will open from the connection after a few seconds.

    Torque/Speed Characteristics

    • The two oppositely directed torques and the resultant torque can be shown effectively with the help of torque-speed characteristics.

    Equivalent Circuit of Single-Phase Induction Motor

    • A single-phase induction motor can be imagined to be consisting of two motors, having a common stator winding, but with their respective rotors revolving in opposite directions.
    • Each rotor has resistance and reactance half the actual rotor values.
    • The two equivalent circuits are connected in series.
    • The current, power, and torque can be calculated from the combined equivalent circuit using network basics.

    Review Questions

    • What is a single-phase induction motor?
    • How does a single-phase induction motor work?
    • How do you test a single-phase motor?
    • Which capacitor is used in a single-phase motor?
    • What are the advantages of a single-phase induction motor?
    • What are the applications of a single-phase induction motor?

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    Learn about the working of single-phase induction motors, their differences from three-phase motors, and their starting mechanisms.

    More Like This

    Induction Motor Quiz
    3 questions

    Induction Motor Quiz

    BrightRoseQuartz avatar
    BrightRoseQuartz
    Induction Motor Basics Quiz
    10 questions

    Induction Motor Basics Quiz

    HeavenlyFife avatar
    HeavenlyFife
    Induction Motors Fundamentals
    39 questions

    Induction Motors Fundamentals

    SprightlyVision avatar
    SprightlyVision
    Induction Motor Rotor Design
    79 questions

    Induction Motor Rotor Design

    SprightlyVision avatar
    SprightlyVision
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser