Electromagnetic Induction and Transformers
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Electromagnetic Induction and Transformers

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Questions and Answers

In which type of transformer are concentric windings primarily used?

  • Distributed transformer
  • Core type transformer (correct)
  • Step-up transformer
  • Shell type transformer

    • What is the primary function of the transformer tank?

  • To regulate voltage output
  • To support the transformer physically
  • To increase transformer efficiency
  • To provide insulation and cooling (correct)

    • How does the conservator in a transformer manage the oil during temperature changes?

  • By allowing expansion and contraction within an air-tight drum (correct)
  • By completely draining and refilling oil
  • By releasing excess oil into the environment
  • By incorporating a pump system for oil circulation

    • What material are the terminal bushings typically made of?

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

    What role does the breather play in a transformer?

    <p>It absorbs atmospheric moisture before it enters the transformer</p> Signup and view all the answers

    What occurs when the Buchholz relay detects an incipient fault?

    <p>It gives an alarm for preventive action</p> Signup and view all the answers

    Why is the oil in a transformer tank not directly exposed to air?

    <p>To prevent oxidation of the oil</p> Signup and view all the answers

    What happens when the oil in the transformer heats up?

    <p>It expands and displaces air into the conservator</p> Signup and view all the answers

    What happens if a serious fault condition occurs in the transformer?

    <p>It gives a tripping command to isolate the transformer.</p> Signup and view all the answers

    What is the purpose of the explosion vent in a transformer?

    <p>To release excessive pressure inside the tank.</p> Signup and view all the answers

    Which winding receives energy from the supply system in a transformer?

    <p>Primary winding</p> Signup and view all the answers

    What core material is typically used in transformers to enhance magnetic coupling?

    <p>Laminated steel</p> Signup and view all the answers

    What phenomenon describes the induced e.m.f. in the secondary winding due to current in the primary winding?

    <p>Mutual induction</p> Signup and view all the answers

    How is the frequency of the induced e.m.f. in the secondary winding related to the supply voltage?

    <p>It is the same as that of the supply voltage.</p> Signup and view all the answers

    What is created in the primary winding when an alternating current flows through it?

    <p>An alternating magnetic flux.</p> Signup and view all the answers

    What are the vertical portions of the transformer core called where the windings are placed?

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

    How does the length of a coil affect its self-inductance?

    <p>Self-inductance decreases with an increase in length.</p> Signup and view all the answers

    Which factor does NOT affect the self-inductance of a coil?

    <p>Type of wire used</p> Signup and view all the answers

    What is the effect of increasing the diameter of a coil on its self-inductance?

    <p>Self-inductance increases.</p> Signup and view all the answers

    When the current in the first coil increases, what type of EMF is induced in that coil?

    <p>Self-induced EMF</p> Signup and view all the answers

    What is the definition of mutually induced EMF?

    <p>EMF induced in a coil due to the change in magnetic field of another coil.</p> Signup and view all the answers

    Which of the following describes the relationship between the number of turns in a coil and its self-inductance?

    <p>Self-inductance increases with the number of turns.</p> Signup and view all the answers

    Which material property is important for increasing a coil's self-inductance?

    <p>Relative permeability of the core material</p> Signup and view all the answers

    What happens to the self-inductance of a coil with an air core compared to one with a magnetic core?

    <p>Air core has the lowest self-inductance.</p> Signup and view all the answers

    Why should a transformer not be connected to a direct current (d.c.) source?

    <p>It produces a constant flux that does not induce e.m.f.</p> Signup and view all the answers

    What is a key feature of a core type transformer?

    <p>The windings are cylindrical and placed on separate limbs.</p> Signup and view all the answers

    Which of the following best describes the winding arrangement in a shell type transformer?

    <p>Windings are placed alternately like a sandwich.</p> Signup and view all the answers

    What feature makes maintenance more difficult in shell type transformers compared to core type transformers?

    <p>The windings are tightly laminated.</p> Signup and view all the answers

    Which transformer type is characterized by having a single magnetic circuit?

    <p>Core type transformer</p> Signup and view all the answers

    What may happen if a d.c. supply is connected to the primary winding of a transformer?

    <p>The transformer may draw a large amount of current.</p> Signup and view all the answers

    In which arrangement does a shell type transformer provide low reactance paths?

    <p>On the outer limb.</p> Signup and view all the answers

    What is an advantage of natural cooling in core type transformers?

    <p>It allows for efficient repair processes.</p> Signup and view all the answers

    What is the induced EMF in the primary winding if the turns are 400 and the voltage per turn is 0.5?

    <p>200V</p> Signup and view all the answers

    If the secondary EMF is calculated using $E2 = E1 \times \frac{N2}{N1}$, what is the secondary EMF when $E1$ is 200V, $N2$ is 1000, and $N1$ is 400?

    <p>500V</p> Signup and view all the answers

    What is the maximum flux density $B_m$ calculated with a maximum flux $Ø_m$ of 2.25 mWb and an area of 150 x $10^{-4}$ m²?

    <p>0.15 T</p> Signup and view all the answers

    What is the kVA rating of a transformer if $V1$ is 200V and $I1$ is 12A?

    <p>2.4 kVA</p> Signup and view all the answers

    At full load and 0.8 p.f lagging, what is the efficiency of a transformer with iron loss of 32 W and full load copper loss of 44 W?

    <p>94.04%</p> Signup and view all the answers

    What is the efficiency of the transformer when operating at 70% full load and 0.8 p.f lagging?

    <p>94%</p> Signup and view all the answers

    What is the efficiency at half load for a transformer if the efficiency is noted as 93.31%?

    <p>93.31%</p> Signup and view all the answers

    For a single phase 100 kVA transformer, what is the efficiency at 75% of the full load and 0.9 p.f leading?

    <p>89.5%</p> Signup and view all the answers

    Study Notes

    Self Inductance

    • Self-inductance increases with:
      • Increased diameter of the coil
      • Increased number of turns of the coil
      • Increased relative permeability of the core material
    • Self-inductance decreases with increased length of the coil.
    • Air core coils have the least self-inductance.

    Mutually Induced EMF

    • Mutually Induced EMF is caused by the change in magnetic flux produced by one coil that links with another coil.
    • The EMF is induced in one coil due to the change in current flowing through another coil.

    Transformers

    • Transformers transfer energy from one circuit to another via magnetic coupling.
    • Concentric windings are used in core-type transformers.
    • Sandwiched windings are used in shell-type transformers.
    • Transformers use a tank filled with oil for insulation and cooling.
    • Devices that protect the transformer from damage include:
      • Buchholz relay
      • Explosion vent (relief valve)
      • Breather

    Transformer Operation

    • Operation relies on the principle of mutual induction.
    • The primary winding receives energy from the supply.
    • The secondary winding delivers energy to the load.
    • Transformers cannot be used with direct current (DC) because a constant flux will not induce an EMF.

    Types of Transformers

    • Core-type transformers have a single magnetic circuit and cylindrical windings.
    • Shell-type transformers have a double magnetic circuit and wound on the central limb, with the outer limb providing a low reactance path.

    Transformer Efficiency

    • The efficiency of a transformer is calculated as the output power divided by the input power.
    • Iron loss is the power lost in the core due to hysteresis and eddy currents.
    • Copper loss is the power lost in the windings due to resistance.
    • Efficiency is affected by the load and power factor.

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    Related Documents

    Unit 1-1: Electromagnetism and Transformers PDF

    Description

    This quiz covers key concepts related to self-inductance, mutually induced EMF, and the operation of transformers. Understand the factors affecting self-inductance, how transformers transfer energy, and the safety devices used in transformers. Test your knowledge on these fundamental principles of electromagnetism.

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