Transformer Construction Types Quiz

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Questions and Answers

How can the balance of ampere-turns between the primary and secondary circuits be translated into apparent power balance in an ideal transformer?

Ip Ep = Is Es

What is the equation representing the balance of ampere-turns between the primary and secondary circuits in an ideal transformer on load?

IpNp = IsNs

What is the relationship between the primary and secondary power factors in a transformer on full-load?

They are always nearly the same

What is the term used to refer to the magnitude of complex power in a transformer?

<p>Apparent power</p> Signup and view all the answers

In terms of complex power, what is the relationship between the power supplied to the primary winding and the power delivered to the load by the secondary winding in an ideal transformer?

<p>IVp = IVs * p * s</p> Signup and view all the answers

What condition implies that the primary and secondary power factors are nearly the same on full-load in a transformer?

<p>Vp Ip cosθp = Vs Is cosθs</p> Signup and view all the answers

Who built the first practical modern transformer in 1885?

<p>William Stanley</p> Signup and view all the answers

What is the alternating flux produced at the primary voltage denoted by?

<p>$\Phi$</p> Signup and view all the answers

What does the transformer E.M.F. equation describe?

<p>Voltages induced in the two coils due to the alternating flux.</p> Signup and view all the answers

In the transformer E.M.F. equation, what does Φ represent?

<p>Alternating flux produced at the primary voltage</p> Signup and view all the answers

What is the core made up of in the first practical modern transformer built by William Stanley?

<p>Individual sheets of metal (laminations)</p> Signup and view all the answers

Why is only one high-voltage insulator and lightning arrester needed in the self-protected distribution transformer?

<p>Because one side of the 7200-V line and one side of the primary are grounded.</p> Signup and view all the answers

What is the primary current like when the secondary winding of the transformer is on open-circuit?

<p>The primary current is such that the primary ampere-turns are just sufficient to produce the necessary flux for inducing an e.m.f.</p> Signup and view all the answers

What is the usual percentage of the full-load primary current that the magnetising current represents?

<p>The magnetising current is usually about 3 – 5 per cent of the full-load primary current.</p> Signup and view all the answers

When a load is connected across the secondary terminals, what effect does the secondary current produce?

<p>The secondary current produces a demagnetising effect.</p> Signup and view all the answers

What happens to the e.m.f. induced in the primary winding when a load is connected to the transformer?

<p>The e.m.f. induced in the primary winding is reduced slightly.</p> Signup and view all the answers

How does the primary current change when the e.m.f. induced in the primary winding is reduced?

<p>The primary current increases appreciably.</p> Signup and view all the answers

What is the function of the current produced in the secondary winding when a load is connected?

<p>The secondary current produces a magnetic flux that opposes the change in the flux in the primary winding.</p> Signup and view all the answers

Explain why the appearance of IsNs due to the secondary load current must be counter-balanced in a transformer.

<p>To maintain the conservation of energy principle, the equal and opposite IpNp must be introduced to balance the energy extraction from the secondary.</p> Signup and view all the answers

What is the significance of the rate of EsIs in a transformer and how is it related to the rate of EpIp?

<p>The rate of energy extraction from the secondary (EsIs) must be matched by the introduction of energy at an equal rate in the primary (EpIp) to maintain equilibrium.</p> Signup and view all the answers

Why is it important to have equal and opposite currents in the primary and secondary of a transformer?

<p>Having equal and opposite currents (IpNp and IsNs) ensures that the energy balance required for efficient operation of the transformer is maintained.</p> Signup and view all the answers

How does the conservation of energy principle apply to the operation of an ideal transformer?

<p>In an ideal transformer, the conservation of energy principle requires that the energy input in the primary side equals the energy output in the secondary side.</p> Signup and view all the answers

Explain the relationship between VsIs and VpIp in the context of energy transfer in a transformer.

<p>VsIs represents the energy extraction rate from the secondary, which should be balanced by the energy introduction rate VpIp in the primary.</p> Signup and view all the answers

What role does the equal and opposite energy introduction rate EpIp play in the operation of a transformer?

<p>EpIp, being equal and opposite to EsIs, ensures that the energy balance is maintained between the primary and secondary sides of the transformer.</p> Signup and view all the answers

What are the conditions in an ideal transformer where equation 4.6 holds exactly?

<p>No voltage drops in resistance or leakage reactance, vanishingly small m.m.f. required to maintain main flux, and no core loss</p> Signup and view all the answers

Describe the phase relations in an ideal transformer according to Figure 4.3(c).

<p>Primary voltage Vp is in phase with Ep, secondary terminal voltage Vs is equal to Es</p> Signup and view all the answers

What determines the phase and magnitude of the secondary current in an ideal transformer?

<p>Nature and magnitude of the load</p> Signup and view all the answers

What is the relationship between secondary m.m.f. and primary m.m.f. in an ideal transformer?

<p>Secondary m.m.f. IsNs is equal and opposite to primary m.m.f. IpNp</p> Signup and view all the answers

Explain the stability conditions in an ideal transformer represented in Figure 4.3(c).

<p>Ep must always be equal to the applied voltage Vp, constant flux Φm inducing Ep, and no resultant m.m.f. in the common magnetic circuit</p> Signup and view all the answers

What are the implications of having no resistance and leakage reactance drops in an ideal transformer?

<p>E.m.f. Ep must always be equal to the applied voltage Vp, constant flux Φm inducing Ep, and no resultant m.m.f. in the common magnetic circuit</p> Signup and view all the answers

Flashcards

Ampere-turns balance (ideal transformer)

The primary and secondary ampere-turns are equal and opposite in an ideal transformer, ensuring power balance.

Transformer equation

IpNp = IsNs ,balancing ampere-turns in an ideal transformer.

Power factors (full-load)

Primary and secondary power factors are nearly the same in a transformer on full load.

Apparent power

The magnitude of complex power in a transformer.

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Transformer power balance

Ideal transformer power supplied to primary equals power delivered to the secondary.

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Ideal transformer condition

Transformer with no losses, ensuring primary and secondary power factor similarity.

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William Stanley

Built the first practical modern transformer (1885).

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Φ (transformer)

Alternating flux produced at the primary voltage in a transformer.

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Transformer EMF equation

Describes voltages induced in transformer coils due to alternating flux.

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Transformer core material

Laminated metal sheets form the core in early practical transformers

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Self-protected distribution transformer

A transformer with only one high-voltage insulator and lightning arrester because one side is grounded.

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Open-circuit primary current

Primary current maintaining necessary flux for induced e.m.f. when secondary is open.

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Magnetising current

Usually 3-5% of full-load current which creates initial magnetic field needed for transformer operation.

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Secondary current effect (load)

Secondary current produces a demagnetizing effect when load is connected.

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Primary EMF change (load)

Primary EMF slightly reduced when load connected to secondary.

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Secondary current function (load)

Creates opposing magnetic flux to maintain energy balance when a load is connected.

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Conserving energy principle (transformers)

Energy input in primary side equals energy output in the secondary side.

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Energy transfer balance (transformer)

Energy extraction from secondary (VsIs) must match energy introduction in primary (VpIp) for equilibrium.

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Primary & secondary current balance

Having equal and opposite primary and secondary currents is vital for energy balance during operation.

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Ideal transformer equations

VpIp = VsIs and IpNp = IsNs. These are true in ideal transformers

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Stability conditions (ideal transformer)

Conditions such as flux, voltage, and ampere turns balance.

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Resistance and leakage reactance (ideal transformers)

No losses due to these conditions in an ideal transformer.

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Phase relations (ideal transformer)

Primary voltage (Vp) is in phase with induced voltage (Ep), and secondary voltage (Vs) equals induced voltage (Es).

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Secondary current determination

Secondary current's phase and magnitude are determined by the nature and magnitude of the load.

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Primary and secondary m.m.f.

Primary and secondary magnetomotive forces (m.m.f.) are equal and opposite in an ideal transformer.

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Ideal transformer stability

Conditions include equal voltage and flux, and zero net magnetomotive force.

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Study Notes

Ideal Transformer

  • An ideal transformer on load has a demagnetizing flux, Φs, which is neutralized by the increase in primary ampere-turns (IpNp).
  • The primary ampere-turns (IpNp) and secondary ampere-turns (IsNs) are nearly equal, resulting in a magnetic field (m.m.f) balance: IpNp = IsNs.

Transformer Equations

  • Equation 4.5: IpNp = IsNs
  • Equation 4.6: Ep/Es = Vp/Vs = Np/Ns
  • Equation 4.7: IpEp = IsEs (apparent power balance)
  • Equation 4.7(b): IpVp = IsVs* (complex power balance)

Transformer Construction

  • Core-type transformer: core surrounds the windings
  • Shell-type transformer: windings surround the core
  • Figure 2.2(a) and 2.2(b): shell-type transformer construction
  • Figure 2.3(a): cutaway view of self-protected distribution transformer
  • Figure 2.3(b): typical shell-type transformer
  • Figure 2.3(c): the first practical modern transformer built by William Stanley in 1885

Transformer E.M.F. Equation

  • Equation 3.1(a): Φ = Φmsin2Ï€ft (alternating flux produced at the primary voltage)
  • Equation 4.3(b): Ep/Es = Np/Ns = α
  • Equation 4.4: Ep/Es = Vp/Vs = Np/Ns

Ideal Transformer on Load

  • When a load is connected, the secondary current produces a demagnetizing effect, reducing the flux and e.m.f. induced in the primary winding.
  • The primary current increases to counterbalance the demagnetizing effect, resulting in a magnetic field (m.m.f) balance.

Equivalent Circuit and Phasor Diagrams

  • In an ideal transformer, there are no voltage drops in resistance or leakage reactance, and no core loss.
  • Equation 4.6 holds exactly, and the phase relations are simple: Vp = Ep, Vs = Es, and Ip = Is.
  • The secondary m.m.f. is IsNs, and the primary m.m.f. is IpNp, which is equal and opposite to the secondary m.m.f.

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