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EE-361

VOLTAGE REGULATION & EFFICIENCY

Ozan Keysan

keysan.me

Office: C-113 Tel: 210 7586

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Voltage Regulation

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Voltage Regulation

A transformer's ability to keep its output voltage constant.

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Voltage Regulation

A transformer's ability to keep its output voltage constant.

Ideal transformer:

Vout at No Load = Vout at Full Load

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Voltage Regulation

A transformer's ability to keep its output voltage constant.

Ideal transformer:

Vout at No Load = Vout at Full Load

Practical transformer:

Vout under load is generally smaller than Vout at No Load

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Voltage Regulation

V2(NoLoad)V2(FullLoad)V2(FullLoad)

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Voltage Regulation

V2(NoLoad)V2(FullLoad)V2(FullLoad)

Smaller regulation is better.

Regulation of an ideal transformer = 0

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Voltage Regulation with Phasors

Drawing

Neglect the parallel branch (for now)

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Voltage Regulation

Drawing

Regulation can be calculated at any load.

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Voltage Regulation

  • Inductive: Vreg>0

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Voltage Regulation

  • Inductive: Vreg>0

  • Resistive: Vreg>0

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Voltage Regulation

  • Inductive: Vreg>0

  • Resistive: Vreg>0

  • Capacitive: Vreg=?

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Voltage Regulation

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Voltage Regulation

Burdur GES

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Example:

For the same transformer(1000 VA) used in the previous problem, calculate the voltage regulation at:

a) 0.8 pf lagging rated current

b) 1.0 pf rated current

c) 0.8 pf leading rated current

if the output voltage of the transformer is adjusted to be 115 V, under the given load condition.

You can ignore the parallel branch.

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Transformer Efficiency

Efficiency(η)=PoutPin

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Transformer Efficiency

Efficiency(η)=PoutPin

Efficiency(η)=PoutPout+Losses

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Transformer Efficiency

Efficiency(η)=PoutPin

Efficiency(η)=PinLossesPin

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Transformer Efficiency

  • Constant Losses: Core Losses (Eddy, Hysteresis)

V21Rcore

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Transformer Efficiency

  • Constant Losses: Core Losses (Eddy, Hysteresis)

V21Rcore

  • Variable Losses: Copper Losses

    I21(R1+R2)

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Best Power Transformer

  • Efficiency as high as possible

  • Voltage Regulation close to zero

  • Minimum Cost

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Golden Rule of Engineering Projects

Drawing

You can only pick TWO from these three!

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Temperature Effect

Drawing

How does the resistance change with temperature?

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Temperature Effect

Temperature Coefficient

R(T)=R(T0)(1+αΔT)

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Temperature Effect

Temperature Coefficient

R(T)=R(T0)(1+αΔT)

For copper α = 0.393 % per degree C

Resistivity of copper increases by 30 % from 20 C to 100 C.

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Losses and Cooling

Drawing

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Losses and Cooling: Small Transformers

Drawing

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Losses and Cooling: Large Transformers

Drawing

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Losses and Cooling: Large Transformers

Drawing

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Losses and Cooling: Large Transformers

Drawing

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Drawing

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(Heat Mass, Heat Dissipation Surface Area)

Drawing

Square-Cube Law by Prof. Walter Lewin

Square-cube law, small is mighty

Small is mighty

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Example:

For the same transformer(1000 VA) used in the previous problems, calculate the efficiency at rated current and 0.8 pf lagging (assuming output voltage is 115 V).

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Question:

What is the point that the transformer has maximum efficiency?

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Question:

What is the point that the transformer has maximum efficiency?

  • Full Load / Half Load / No Load ?

  • Unity pf, lagging pf, leading pf?

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Transformer Efficiency

A transformer has highest efficiency while delivering unity pf

Drawing

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A transformer has maximum efficiency when:

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A transformer has maximum efficiency when:

Copper Losses = Core Losses

Drawing

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You can download this presentation from: keysan.me/ee361

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Voltage Regulation

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