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    Dr. TTIT, KGF WWW - Drttit.edu - in Dr. TTIT, KGF WWW - Drttit.edu - in

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    rama Krishna
    This document contains 8 questions divided into 2 parts about transformers and induction machines for a 4th semester B.E. degree examination. The questions cover topics such as the operation of single-phase transformers, transformer equivalent circuits, efficiency calculations, autotransformer comparisons, induction motor characteristics, circle diagrams, and speed control methods. Test takers must answer 5 full questions total, selecting at least 2 questions from each part.

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    Dr. TTIT, KGF WWW - Drttit.edu - in Dr. TTIT, KGF WWW - Drttit.edu - in

    Uploaded by

    rama Krishna
    35 views2 pages
    This document contains 8 questions divided into 2 parts about transformers and induction machines for a 4th semester B.E. degree examination. The questions cover topics such as the operation of single-phase transformers, transformer equivalent circuits, efficiency calculations, autotransformer comparisons, induction motor characteristics, circle diagrams, and speed control methods. Test takers must answer 5 full questions total, selecting at least 2 questions from each part.

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    June15 10EE46

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    This document contains 8 questions divided into 2 parts about transformers and induction machines for a 4th semester B.E. degree examination. The questions cover topics such as the operation of single-phase transformers, transformer equivalent circuits, efficiency calculations, autotransformer comparisons, induction motor characteristics, circle diagrams, and speed control methods. Test takers must answer 5 full questions total, selecting at least 2 questions from each part.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    35 views2 pages

    Dr. TTIT, KGF WWW - Drttit.edu - in Dr. TTIT, KGF WWW - Drttit.edu - in

    Uploaded by

    rama Krishna
    This document contains 8 questions divided into 2 parts about transformers and induction machines for a 4th semester B.E. degree examination. The questions cover topics such as the operation of single-phase transformers, transformer equivalent circuits, efficiency calculations, autotransformer comparisons, induction motor characteristics, circle diagrams, and speed control methods. Test takers must answer 5 full questions total, selecting at least 2 questions from each part.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 2

    USN 10EE46

    Fourth Semester B.E. Degree Examination, June/July 2015


    Transformers and Induction Machines

    Time: 3 hrs. Max. Marks:IOO

    Note: Answer any FIVE full questions, selecting


    atleast TWO questions from each part.

    PART-A

    1 a. Describe the operation of a single-phase transformer, explaining clearly the functions of the
    different parts. (06 Marks)

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    b. Explain the operation of transformer under load condition and hence develop the phasor

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    diagram of a single phase transformer under load condition. (08 Marks)

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    c. A 125 kVA transformer having primary voltage of2000V at 50Hz has 182 primary and 40
    secondary turns. Neglecting losses, calculate: i) full load primary and secondary current;

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    ii) no load secondary induced e.m.f and iii) the maximum flux in the core. (06 Marks)

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    2 a. Develop the exact equivalent circuit of a l-phase transformer. From this derive the
    approximate and simplified equivalent circuits of the transformer. State the various
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    assumptions made. (08 Marks)
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    b. Derive the condition for maximum efficiency. (04 Marks)
    c. A 2300/230 V, 500 kV A, 50 Hz distribution transformer has core loss of 1600 W at rated
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    voltage and copper loss 7.5 kW at full load. During the day it is loaded as follows:
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    % load 0% 20% 50% 80% 100% 125%


    p.f. - 0.7 lag 0.8 lag 0.9 lag 1 0.85 lag
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    Hours 2 4 4 5 7 2
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    Determine the all day efficiency ofthe transformer. (08 Marks)

    3 a. Derive an expression for the saving of copper of autotransformer as compared to an


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    equivalent two-winding transformer. (06 Marks)


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    b. With neat sketch, explain working of constant voltage transformer. (06 Marks)
    c. Two single phase transformers share a load of 400 kV A at power factor of 0.8 lag. Their
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    equivalent impedances referred to secondary winding are (1 + j2.5) Q and (l.5 + j3) n
    respectively. Calculate the load shared by each transformer. (08 Marks)
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    4 a. Draw the Scott connection of transformers and mark the terminals and turn ratio. What are
    the applications of Scott connection? (08 Marks)
    b. Discuss the essential and desirable conditions to be fulfilled for operating two three phase
    transformers in parallel. (04 Marks)
    c. A 400 kVA load at 0.7 pf lagging is supplied by three single phase transformers connected
    in fl - fl. Each of fl - fl transformers is rated at 200 kVA, 2300/230 V. If one defective
    d) transformer is removed from service, calculate for V - V connection:
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    ii)
    The kVA load carried by each transformer.
    Percent rated load carried by each transformer.
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    Q. iii) Total kVA ratings of the transformer bank in V-V.
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    iv) Ratio of V - V bank to fl - fl bank transformer ratings. (08 Marks)

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    PART-B

    5 a. Draw and explain the complete torque-speed characteristic of three phase induction machine
    for all ranges of speed. (06 Marks)
    b. Explain the concept of rotating magnetic field in 3-phase induction motor. (06 Marks)
    c. A 746 kW, 3-phase, 50Hz, 16-pole induction motor has a rotor impedance of
    (0.02 + jO.15) n at stand still. Full load torque is obtained at 360 rpm. Calculate:
    i) The speed at which maximum torque occurs; ii) The ratio of maximum to full-load
    torque; iii) The external resistance per phase to be inserted in the rotor circuit to get
    maximum torque at starting. (08 Marks)

    6 a. Explain cogging and crawling phenomenon in 3-<1> induction motor. (06 Marks)
    b. A 50 kW, 6-pole, 50 Hz, 450 V, 3-<1>induction motor furnished the following test figures: No
    load test: 450 V, 20A, p.f = 0.15. Blocked rotor test: 200V, 150A, pf= 0.3. The ratio of

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    stator to rotor copper losses on short circuit was 5:4. Draw circle diagram and determine
    from it.

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    i) Full load current and p.f

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    ii) Maximum torque and maximum power input.

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    iii) Slip at full load.
    iv) Efficiency at full load. (14 Marks)

    7
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    a. Describe with sketch, the construction of a double cage induction motor. (07 Marks)
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    b. Explain with sketch deep-bar cage motor. (06 Marks)
    c. Explain theory of self excited induction generator.
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    (07 Marks)
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    8 a. With neat sketch, explain auto transformer starter. -{06.Marks)


    b. With neat diagram, explain shaded pole single phase motor.
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    (06 Marks)
    c. Briefly explain different speed control methods of3-<I>induction motor. (08 Marks)
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    *****
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