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Questions and Answers
In which type of transformer are concentric windings primarily used?
In which type of transformer are concentric windings primarily used?
What is the primary function of the transformer tank?
What is the primary function of the transformer tank?
How does the conservator in a transformer manage the oil during temperature changes?
How does the conservator in a transformer manage the oil during temperature changes?
What material are the terminal bushings typically made of?
What material are the terminal bushings typically made of?
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What role does the breather play in a transformer?
What role does the breather play in a transformer?
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What occurs when the Buchholz relay detects an incipient fault?
What occurs when the Buchholz relay detects an incipient fault?
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Why is the oil in a transformer tank not directly exposed to air?
Why is the oil in a transformer tank not directly exposed to air?
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What happens when the oil in the transformer heats up?
What happens when the oil in the transformer heats up?
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What happens if a serious fault condition occurs in the transformer?
What happens if a serious fault condition occurs in the transformer?
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What is the purpose of the explosion vent in a transformer?
What is the purpose of the explosion vent in a transformer?
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Which winding receives energy from the supply system in a transformer?
Which winding receives energy from the supply system in a transformer?
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What core material is typically used in transformers to enhance magnetic coupling?
What core material is typically used in transformers to enhance magnetic coupling?
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What phenomenon describes the induced e.m.f. in the secondary winding due to current in the primary winding?
What phenomenon describes the induced e.m.f. in the secondary winding due to current in the primary winding?
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How is the frequency of the induced e.m.f. in the secondary winding related to the supply voltage?
How is the frequency of the induced e.m.f. in the secondary winding related to the supply voltage?
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What is created in the primary winding when an alternating current flows through it?
What is created in the primary winding when an alternating current flows through it?
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What are the vertical portions of the transformer core called where the windings are placed?
What are the vertical portions of the transformer core called where the windings are placed?
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How does the length of a coil affect its self-inductance?
How does the length of a coil affect its self-inductance?
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Which factor does NOT affect the self-inductance of a coil?
Which factor does NOT affect the self-inductance of a coil?
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What is the effect of increasing the diameter of a coil on its self-inductance?
What is the effect of increasing the diameter of a coil on its self-inductance?
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When the current in the first coil increases, what type of EMF is induced in that coil?
When the current in the first coil increases, what type of EMF is induced in that coil?
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What is the definition of mutually induced EMF?
What is the definition of mutually induced EMF?
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Which of the following describes the relationship between the number of turns in a coil and its self-inductance?
Which of the following describes the relationship between the number of turns in a coil and its self-inductance?
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Which material property is important for increasing a coil's self-inductance?
Which material property is important for increasing a coil's self-inductance?
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What happens to the self-inductance of a coil with an air core compared to one with a magnetic core?
What happens to the self-inductance of a coil with an air core compared to one with a magnetic core?
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Why should a transformer not be connected to a direct current (d.c.) source?
Why should a transformer not be connected to a direct current (d.c.) source?
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What is a key feature of a core type transformer?
What is a key feature of a core type transformer?
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Which of the following best describes the winding arrangement in a shell type transformer?
Which of the following best describes the winding arrangement in a shell type transformer?
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What feature makes maintenance more difficult in shell type transformers compared to core type transformers?
What feature makes maintenance more difficult in shell type transformers compared to core type transformers?
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Which transformer type is characterized by having a single magnetic circuit?
Which transformer type is characterized by having a single magnetic circuit?
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What may happen if a d.c. supply is connected to the primary winding of a transformer?
What may happen if a d.c. supply is connected to the primary winding of a transformer?
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In which arrangement does a shell type transformer provide low reactance paths?
In which arrangement does a shell type transformer provide low reactance paths?
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What is an advantage of natural cooling in core type transformers?
What is an advantage of natural cooling in core type transformers?
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What is the induced EMF in the primary winding if the turns are 400 and the voltage per turn is 0.5?
What is the induced EMF in the primary winding if the turns are 400 and the voltage per turn is 0.5?
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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?
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?
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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?
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?
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What is the kVA rating of a transformer if $V1$ is 200V and $I1$ is 12A?
What is the kVA rating of a transformer if $V1$ is 200V and $I1$ is 12A?
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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?
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?
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What is the efficiency of the transformer when operating at 70% full load and 0.8 p.f lagging?
What is the efficiency of the transformer when operating at 70% full load and 0.8 p.f lagging?
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What is the efficiency at half load for a transformer if the efficiency is noted as 93.31%?
What is the efficiency at half load for a transformer if the efficiency is noted as 93.31%?
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For a single phase 100 kVA transformer, what is the efficiency at 75% of the full load and 0.9 p.f leading?
For a single phase 100 kVA transformer, what is the efficiency at 75% of the full load and 0.9 p.f leading?
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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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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.
