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    Induction Motor Tests

    Uploaded by

    Victor Odoyo
    The paper gives an overview of no-load and blocked rotor tests performed in a laboratory with their circuit diagrams.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd

    Induction Motor Tests

    Uploaded by

    Victor Odoyo
    62 views4 pages
    The paper gives an overview of no-load and blocked rotor tests performed in a laboratory with their circuit diagrams.

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    © © All Rights Reserved

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    PDF, TXT or read online from Scribd

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    The paper gives an overview of no-load and blocked rotor tests performed in a laboratory with their circuit diagrams.

    Copyright:

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

    Induction Motor Tests

    Uploaded by

    Victor Odoyo
    The paper gives an overview of no-load and blocked rotor tests performed in a laboratory with their circuit diagrams.

    Copyright:

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

    THE TECHNICAL UNIVERSITY OF KENYA

    Haile Selassie Avenue, P. O. Box 52428, Nairobi, 00200, Tel: +254 (020) 343672, 2249974, 2251300, 341639,
    Fax: 2219689, E-mail: vc@kenpoly.ac.ke, Website: www.tukenya.ac.ke

    FACULTY OF ENGINEERING AND BUILT ENVIRONMENT


    School of Electrical and Electronics Engineering
    Bachelor of Engineering Year 5
    INDUCTION MOTOR TESTS

    AIMS

     To perform no-load and blocked rotor tests on a three phase squirrel cage induction motor.
     To determine the machine parameters based on the above tests.

    BACK GROUND INFORMATION

    No-load test is performed to determine no-load power factor, core or iron loss, windage and friction loss,
    copper loss and no-load resistance and reactance. In this test, the motor is run without any external
    mechanical load on it. The test is carried out with different values of applied voltage above and below the
    rated voltage (approximately 20% higher and lower than the rated voltage respectively). As the motor is
    running light, the power factor is less than 0.5 and the total power input will be the algebraic sum of the
    two wattmeter readings. The curve plotted of no-load power verses applied voltage is extrapolated to
    separate loss due to friction and windage from the no-load electrical and magnetic losses collectively
    known as stator copper loss and core loss respectively.

    Blocked rotor test is performed to determine short circuit current with normal voltage applied to stator,
    power factor on short circuit, total equivalent resistance and reactance of the motor as referred to the
    stator side. Windage and friction losses are absent, core losses being very small and can be neglected for
    practical purposes thus power input during this test can be considered entirely stator and rotor copper
    losses. In this test, the rotor is locked and the rotor windings are short-circuited at slip rings in case of a
    wound rotor motor. A reduced voltage is applied to the stator terminals and is so adjusted that full load
    current flows in the stator. The curve plotted of stator current verses applied voltage is approximately a
    straight line.

    Induction Machines 1
    USEFUL FORMULAE

    No-load Power factor Cosϕo = Po/√3VLIo

    Energy component of no-load phase current Ie = IoCosØo

    Magnetizing component of no-load phase current Im = √(Io2- Ie2)

    No-load impedance Zo = (VL/√3)/Io

    No-load resistance Ro = (VL/√3)/Ie

    No-load reactance Xo = VL/√3)/Im

    Motor equivalent resistance per phase as referred to stator, R 01 = PSC/3ISC2

    Motor equivalent impedance per phase as referred to stator, Z 01 = (VSC/√3)/ ISC

    EQUIPMENT AND INSTRUMENTS

     Power supply: three-phase variable line 0 - 430V


     Moving-iron ammeter 2-4A
     Moving-iron voltmeter 250-500V
     2 electrodynamic wattmeters 2.5-5A/250-500V
     Three phase squirrel cage induction motor, model M-4/EV
     Eddy current brake equipment, model FE/EV
    CIRCUIT DIAGRAM

    Figure 1

    MEDIA: Interactive Lab Assistant; High-voltage A.C Machines

    Induction Machines 2
    PROCEDURE

    Necessary precautions must be observed while performing these tests. Blocked rotor test must be carried
    out quickly to prevent excessive heating of the machine

    STEPS FOR PERFORMING NO LOAD TEST:


    1. Connect the circuit as shown in figure 1.
    2. Start the motor at maximum voltage, allow it to run for some time, reduce the terminal voltage in
    steps of 50V up to a minimum of 270V taking corresponding values of no-load currents and
    powers measured by the two wattmeters.
    3. Switch off the power supply.
    STEPS FOR PERFORMING BLOCKED ROTOR TEST:
    1. Block the rotor by the proper blocking device; machine model FE/EV.
    2. At first, a current equal to the rated one (or even 20% higher) must cross the line of the motor;
    acting on the voltage variator, increase the voltage slowly until the stator current reads 2A (do not
    exceed this value), measure the supply voltage and read the indications of the wattmeters.
    3. Take few other readings for gradually decreasing currents as shown in table 2 below.
    4. Switch off the power supply.

    Table 1: No load test results

    Vo Io (A) W1 W2 W1 + W2

    Table 2: Blocked rotor test results

    VSC ISC (A) W1 W2 W1 + W2

    2.0

    1.5

    1.0

    0.5

    Induction Machines 3
    DISCUSSION
    With reference to the above experiment:
    i. What machine parameters can be obtained from no-load test?

    ii. Even though there is no-load, why is the wattmeter reading not zero?

    iii. No load test is conducted at (a) nearly rated current, (b) nearly rated voltage, (c) zero
    current, (d) zero voltage (e) none of the above; [Choose the correct answer].

    iv. Which loss in the machine is significant in no load test?

    v. Calculate the no-load resistance and reactance.


    vi. Plot the curve of no-load power verses applied voltage hence separate loss due to friction
    and windage from the no-load electrical and magnetic losses.
    vii. Blocked rotor test is conducted at (a) nearly rated current, (b) nearly rated voltage, (c)
    rated current, (d) rated voltage (e) zero current, (f) zero voltage (g) none of the above;
    [Choose the correct answer].

    viii. The curve plotted of stator current verses applied voltage in blocked rotor test is
    approximately a straight line. Explain.
    ix. Which loss in the machine is significant in blocked rotor test?
    x. Find the motor equivalent reactance per phase as referred to the stator.

    Induction Machines 4

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