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    Lab Final Exam Answer PDF

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    helen tsegay
    This document provides an answer key for an electrical engineering laboratory exam. It includes explanations of terms like slip and blocked rotor test for induction motors, precautions for DC shunt motors, why induction motors are called rotating transformers, advantages of delta-delta transformer configurations, transformer equivalent circuit parameters from open and short circuit tests, and flux control speed control for DC shunt motors. Circuit diagrams are provided for short circuit tests, speed control, and field current-speed characteristics. Parameters like core loss resistance, magnetizing reactance, total equivalent resistance and reactance are calculated from transformer test data.

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    Lab Final Exam Answer PDF

    Uploaded by

    helen tsegay
    137 views4 pages
    This document provides an answer key for an electrical engineering laboratory exam. It includes explanations of terms like slip and blocked rotor test for induction motors, precautions for DC shunt motors, why induction motors are called rotating transformers, advantages of delta-delta transformer configurations, transformer equivalent circuit parameters from open and short circuit tests, and flux control speed control for DC shunt motors. Circuit diagrams are provided for short circuit tests, speed control, and field current-speed characteristics. Parameters like core loss resistance, magnetizing reactance, total equivalent resistance and reactance are calculated from transformer test data.

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    This document provides an answer key for an electrical engineering laboratory exam. It includes explanations of terms like slip and blocked rotor test for induction motors, precautions for DC shunt motors, why induction motors are called rotating transformers, advantages of delta-delta transformer configurations, transformer equivalent circuit parameters from open and short circuit tests, and flux control speed control for DC shunt motors. Circuit diagrams are provided for short circuit tests, speed control, and field current-speed characteristics. Parameters like core loss resistance, magnetizing reactance, total equivalent resistance and reactance are calculated from transformer test data.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    137 views4 pages

    Lab Final Exam Answer PDF

    Uploaded by

    helen tsegay
    This document provides an answer key for an electrical engineering laboratory exam. It includes explanations of terms like slip and blocked rotor test for induction motors, precautions for DC shunt motors, why induction motors are called rotating transformers, advantages of delta-delta transformer configurations, transformer equivalent circuit parameters from open and short circuit tests, and flux control speed control for DC shunt motors. Circuit diagrams are provided for short circuit tests, speed control, and field current-speed characteristics. Parameters like core loss resistance, magnetizing reactance, total equivalent resistance and reactance are calculated from transformer test data.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 4

    Course Title: Electrical Engineering Laboratory-IV Course code: ECEG-3132

    FINAL EXAM: Answer Key

    Part-I: Explanation (15 points)

    1. What is meant by ‘Slip’ of the motor


    This difference between the speed of the rotor and speed of the rotating magnetic field in the
    stator is called slip. It is unitless and is the ratio between the relative speed of the magnetic
    field as seen by the rotor to the speed of the rotating field. Due to this an induction motor is
    sometimes referred to as an asynchronous machine.
    what is the approximate value of slip of 3-phase induction motor in blocked rotor test?
    The slip for the blocked rotor test is unity since the rotor is stationary and the resistance of
    the rotor branch of the equivalent circuit becomes very small (i.e. R2/sis just equal to R2).
    Thus, the rotor current is much larger than current in the excitation branch of the circuit such
    that the excitation branch can be neglected.

    2. What is the most important precaution in any experiment with D.C. shunt motor? ( 3
    points)
    Before switching on d.c. supply, a sufficient resistance should be put in series with the
    armature of the d.c. shunt motor.
    o maximum resistance must be in the armature circuit
    o minimum resistance in the field circuit.

    3. Why an Induction motor sometimes called Rotating Transformer? ( 2 points)


    An induction motor is sometimes called a rotating transformer because the stator (stationary
    part) is essentially the primary side of the transformer and the rotor (rotating part) is the
    secondary side.
    4. State the advantage of delta-delta configuration compared to the star-delta
    configuration in 3- phase transformer. ( 2 points)
    The delta-delta connection nevertheless has one big advantage over the star-delta
    configuration, in that if one transformer of a group of three should become faulty or disabled,
    the two remaining ones will continue to deliver three-phase power with a capacity equal to
    approximately two thirds of the original output from the transformer unit.
    5. Write the EMF equation of a transformer and what is determined from open circuit
    test of single phase transformer? ( 2 point)
    Erms = 4.44 Fm fN V
    Where,
    Fm = maximum value of the flux linkage with both the windings,
    f = frequency of the supply,
    N = number of turns.
    what is determined from open circuit test of single phase transformer?
    Iron loss. Shunt parameters Rc and Xm

    6. What is the use of iron core in a transformer? ( 2 points)


    The iron core is used in a transformer to provide continuous easy magnetic path of low
    reluctance.
    7. If the rated speed of a D.C shunt motor is 1440 rpm, which method of speed control
    would you suggested to obtain a speed of 1500 rpm? ( 1 point)
    Field ( flux) control method of speed control is suggested.

    Part-II: Circuit Diagrams (5 points)

    8. Draw the circuit diagram for Short Circuit Test of 1-ф Transformer and include all the
    required measuring instruments. (2 points)

    9. Draw the circuit diagram of speed control DC shunt motor and include all the required
    measuring instruments. (2 points)
    10. Draw the field current- Speed characteristics of a DC shunt motor in flux control method of
    speed control. (1 point)

    Part-II: Work out (10 points)

    11. Following data are taken from open circuit (OC) and short circuit (SC) test of single phase
    115/230 V transformer.
    Open circuit (OC) test Short Circuit (SC) test
    V0 = 230 V Vsc = 25 V
    I0 = 0.48 V Isc = 4.284 V
    W0 = 50 W Wsc = 90 W
    a) Draw the Approximate equivalent circuit of single phase transformer (2 points)

    b) Determine the following transformer parameters.


    (i) Core loss resistance, Rc ( 2 points)
    (ii) Magnetizing reactance, Xm ( 2 points)
    (iii) Total equivalent resistance referred to Primary side, R eq ( 2 points)
    (iv) Total equivalent reactance referred to Primary side, Xeq ( 2 points)

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