Transformer Basics and Types Quiz
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Questions and Answers

What is the significance of having the primary and secondary windings close to each other in a transformer?

  • It enhances mutual inductance. (correct)
  • It allows higher voltage operation.
  • It increases the leakage flux.
  • It reduces the number of turns required.

What type of coils are typically used in a core type transformer?

  • Square-shaped coils
  • Cylindrical concentric coils (correct)
  • Sandwich coils
  • Layered disk coils

How does subdivision of windings into smaller portions affect transformer performance?

  • It decreases current handling capacity.
  • It increases core losses.
  • It reduces leakage flux. (correct)
  • It increases the overall winding resistance.

In a typical transformer, where is the low voltage winding usually placed?

<p>Near the core for ease of insulation. (B)</p> Signup and view all the answers

What is a primary characteristic of sandwich coils used in transformers?

<p>They have low voltage portions surrounding the high voltage portion. (C)</p> Signup and view all the answers

Which factor is primarily considered when classifying transformers?

<p>The arrangement of the core and windings. (C)</p> Signup and view all the answers

What material is commonly used for insulating different layers of coils in transformers?

<p>Paper (B)</p> Signup and view all the answers

Which design increases the mechanical strength of coils in a transformer?

<p>Cylindrical concentric coils (B)</p> Signup and view all the answers

What does a turns ratio of 5:2 signify in a transformer?

<p>2 volts on the secondary winding for every 5 volts on the primary winding (B)</p> Signup and view all the answers

What is the role of the primary coil in a transformer?

<p>It is connected to an AC voltage source. (B)</p> Signup and view all the answers

What occurs when the current in one coil of a transformer changes uniformly?

<p>An electromotive force is induced in the secondary coil. (A)</p> Signup and view all the answers

How is electric energy transferred in a basic transformer setup?

<p>Entirely through magnetic induction. (C)</p> Signup and view all the answers

Which statement accurately reflects Faraday's Laws of Electromagnetic Induction in the context of transformers?

<p>The induced e.m.f. is related to the rate of change of current in the coil. (A)</p> Signup and view all the answers

Why can't DC currents be used in transformers?

<p>DC currents cannot change due to constant supply. (A)</p> Signup and view all the answers

What is the primary voltage if the transformer has 100 primary windings and 350 secondary windings, with a secondary voltage of 700V?

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

In a transformer with 60 primary and 100 secondary windings, if the secondary voltage is 250V, what is the primary voltage?

<p>150V (A)</p> Signup and view all the answers

What is the output voltage if a transformer with 50 primary loops and an input voltage of 120V is required to produce 100kV in the secondary?

<p>100000V (A)</p> Signup and view all the answers

What is the primary purpose of electric machines?

<p>To convert between mechanical and electrical energy. (C)</p> Signup and view all the answers

What is the primary current if the transformer with a primary voltage of 120V draws a current of 10A?

<p>10A (A)</p> Signup and view all the answers

When a transformer is described as 'step-up', what is true about its primary and secondary voltages?

<p>Primary voltage is less than secondary voltage. (A)</p> Signup and view all the answers

Which of the following machines is classified as a static electrical machine?

<p>Transformer (A)</p> Signup and view all the answers

What principle does a transformer operate on?

<p>Self and mutual induction (D)</p> Signup and view all the answers

In a step-down transformer, how is the number of secondary windings in comparison to the primary windings?

<p>It is less than primary windings. (A)</p> Signup and view all the answers

What must happen to the current in one coil for a transformer to work effectively?

<p>It must change uniformly. (C)</p> Signup and view all the answers

What is the main advantage of alternating currents over direct currents?

<p>They can be easily transformed between different voltage levels. (B)</p> Signup and view all the answers

Which of the following is NOT a method to generate electricity?

<p>Electric motors (D)</p> Signup and view all the answers

During the operation of a transformer, which aspect remains unchanged?

<p>Frequency (A)</p> Signup and view all the answers

What is the role of motors in electric machines?

<p>They convert electrical energy into mechanical energy. (B)</p> Signup and view all the answers

Which type of electric machine is used to convert mechanical energy into electrical energy?

<p>Generator (D)</p> Signup and view all the answers

What is the average e.m.f. per turn according to Faraday's law?

<p>$4.44f \Phi_m$ volts (C)</p> Signup and view all the answers

What does the term 'K' represent in the context of transformers?

<p>The ratio of secondary to primary induced e.m.f. (A)</p> Signup and view all the answers

How is the R.M.S value of induced e.m.f. for whole secondary windings expressed?

<p>$N_2 \times 4.44f \Phi_m$ volts (A)</p> Signup and view all the answers

What is the significance of the factor 1.11 in the context of the R.M.S value?

<p>It is the factor by which the average value is converted to R.M.S value. (C)</p> Signup and view all the answers

How does the average e.m.f. per turn relate to the rate of change of flux?

<p>It is directly proportional to the rate of change of flux. (A)</p> Signup and view all the answers

What does the term 'turn ratio' refer to in transformer equations?

<p>The ratio of number of turns in primary to number of turns in secondary (D)</p> Signup and view all the answers

What occurs to the flux in the core during one quarter of the cycle?

<p>It increases sinusoidally from zero to maximum. (D)</p> Signup and view all the answers

What is the formula for the average e.m.f. in the primary winding (E1)?

<p>$4.44f \Phi_m N_1$ volts (B)</p> Signup and view all the answers

What is the primary function of a transformer?

<p>To increase or decrease voltage levels (A)</p> Signup and view all the answers

In a step-up transformer, how does the number of turns in the primary coil compare to the secondary coil?

<p>Less than the secondary coil (B)</p> Signup and view all the answers

What type of current do transformers typically operate with?

<p>Alternating Current (AC) (B)</p> Signup and view all the answers

What equation represents the relationship between the input and output voltages of a transformer?

<p>$E_1/N_1 = E_2/N_2$ (D)</p> Signup and view all the answers

What is the peak value of flux density if the primary voltage is 520 V, with 400 turns, at a frequency of 50 Hz?

<p>0.976 Wb/m2 (A)</p> Signup and view all the answers

Which of the following components is the main factor that enables a transformer to function?

<p>Electromagnetic induction (D)</p> Signup and view all the answers

What happens to the current output when using large voltages in transformer demonstrations?

<p>Current decreases significantly (A)</p> Signup and view all the answers

If a transformer has a secondary voltage of 1300 V and a primary voltage of 520 V, what is the ratio of the number of turns between the primary and secondary?

<p>1:2.5 (D)</p> Signup and view all the answers

Flashcards

Electrical Generation

The process of converting mechanical energy into electrical energy.

Electrical Motor

The process of converting electrical energy into mechanical energy.

Transformers

Devices that transfer electrical energy from one circuit to another, changing the voltage and current but not the frequency.

Mutual Induction

The ability of one coil to induce a voltage in another coil nearby, without direct contact.

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Static Electric Machine

A type of electrical machine that does not have moving parts and relies on the principle of mutual induction.

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Rotating Electric Machine

A type of electrical machine that has moving parts and converts electrical energy to mechanical energy or vice versa.

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Generator

A device that converts mechanical energy into electrical energy using electromagnetic induction.

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Motor

A device that converts electrical energy into mechanical energy using electromagnetic induction.

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Turns Ratio

The ratio of the number of turns in the primary winding to the number of turns in the secondary winding of a transformer.

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Primary Winding

The coil in a transformer connected to the voltage source.

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Secondary Winding

The coil in a transformer connected to the load.

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Step-up transformer

A type of transformer where the secondary voltage is higher than the primary voltage, meaning it 'steps up' the voltage.

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Step-down transformer

A type of transformer where the secondary voltage is lower than the primary voltage, meaning it 'steps down' the voltage.

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Secondary current

The current in the secondary coil of a transformer.

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Primary current

The current in the primary coil of a transformer.

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Secondary voltage

The voltage in the secondary coil of a transformer.

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What is N1 in a transformer?

The number of turns on the primary winding of a transformer.

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What is N2 in a transformer?

The number of turns on the secondary winding(s) of a transformer.

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How does the cross-section of a transformer limb vary?

The cross-section of a transformer limb depends on the coil type (circular or rectangular) and the transformer size. Small transformers often have circular limbs, while large transformers have rectangular limbs.

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What is leakage flux?

Leakage flux is the magnetic flux that does not link both windings of a transformer. It can reduce efficiency and performance.

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What are concentric coils and how do they improve transformer performance?

When two windings in a transformer are split into multiple coils and wound adjacent to each other on the same limb. This reduces leakage flux and increases mutual inductance.

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What are cylindrical concentric coils?

Used in core type transformers, these coils are mechanically strong and wound in helical layers, with insulation between layers.

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What are sandwich coils?

A type of coil used in shell type transformers, where each high voltage section is sandwiched between two low voltage sections.

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How does subdividing windings affect leakage flux and reactance?

The subdivision of windings into smaller portions reduces leakage flux and reactance. The more subdivisions, the lower the reactance.

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Transformer Action

The process of using electromagnetic induction to transfer electrical energy between circuits at different voltage levels.

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Flux Density

The magnetic flux density in the core of a transformer, influenced by the current flowing through the windings.

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Transformer Power

The amount of energy transferred through a transformer is determined by the product of the voltage and current.

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Average Rate of Change of Flux

The average rate of change of magnetic flux in a coil, directly proportional to the average induced electromotive force (e.m.f.) across the coil.

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Sinusoidal Flux Variation

The sinusoidal variation of magnetic flux in a transformer core, peaking at a maximum value (Ï•m) and reaching zero at the end of a quarter cycle.

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Time Period for Flux Change

The time it takes for the magnetic flux to change from zero to its maximum value (Ï•m) in a transformer core, equivalent to one quarter of the full cycle time (1/4f).

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RMS Value of Induced e.m.f. per Turn

The root-mean-square (RMS) value of induced e.m.f. per turn in a transformer winding, calculated as 4.44fΦm, where 'f' is the frequency and 'Φm' is the maximum flux.

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Voltage Transformation Ratio

The ratio of the secondary induced e.m.f. (E2) to the primary induced e.m.f. (E1) in a transformer, represented as K; also equal to the ratio of the number of turns in the secondary winding (N2) to the number of turns in the primary winding (N1).

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e.m.f. Equations of Transformer

The equations that express the induced e.m.f. in the primary and secondary windings of a transformer, considering the number of turns, frequency, and maximum flux: E1 = 4.44f Φm N1 and E2 = 4.44f Φm N2.

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Equal e.m.f. per Turn

The fact that the induced e.m.f. per turn in the primary winding (N1) is equal to the induced e.m.f. per turn in the secondary winding (N2) in a transformer.

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Study Notes

Transformer Basics

  • Transformers are static electrical devices that transfer electrical energy between two circuits
  • They do this without a direct electrical connection
  • The core principle is mutual induction
  • Two coils (primary and secondary) are wound around a ferromagnetic core

Transformer Types

  • Core type
    • Single magnetic circuit
    • Core is rectangular
    • Windings encircle core
    • Cylindrical coils
  • Shell type
    • Double magnetic circuit
    • Core has three limbs
    • Windings placed on central limb
    • Multilayer disc or sandwich coils
  • Berry type
    • Distributed magnetic circuits
    • More than two magnetic circuits
    • Core construction like spokes of a wheel
    • Symmetrical to shell type
    • Tanks filled with insulating oil

Transformer Construction

  • Two windings wound on separate limbs
  • Soft iron core provides magnetic circuit
  • Laminated core to reduce eddy currents
  • Insulating materials between windings and core
  • Insulating materials between layers of winding coils

Principle of Operation

  • Mutual Induction
  • Alternating current (AC) in primary winding creates alternating magnetic flux
  • Changing flux induces voltage in secondary winding
  • Voltage ratio is determined by turns ratio (N2/N1)
    • Step-up transformer = N2>N1; increases voltage
    • Step-down transformer = N2<N1; decreases voltage

Transformer Equations

  • Voltage ratio (K) = E2/E1 = N2/N1
  • Current ratio = I2/I1 = N1/N2
  • Transformer efficiency is typically high

Transformer Applications

  • Electrical power distribution (stepping up/down voltage)
  • Industrial machinery
  • Household appliances.

Transformer Losses

  • Eddy currents in the core (reducing with laminated core)
  • Hysteresis losses in the core (reducing with higher quality core materials)
  • Resistance losses in wires
  • Leakage flux affecting transformer efficiency.

Transformer Exercises

  • DC cannot be used in transformers because the current does not uniformly change
  • Exercises provided show how to calculate voltage and turns based on the known quantities for primary turns, secondary turns, secondary voltage

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Description

Test your knowledge on the fundamentals of transformers, including their basic principles, different types, and construction methods. This quiz covers essential concepts such as mutual induction, core types, and the materials used in transformer design.

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