Power Generation and Transmission Quiz

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Questions and Answers

What is the primary advantage of AAAC conductors over ACSR conductors?

  • Better electrical insulation
  • Lower conductivity
  • Higher strength
  • Lighter weight and better corrosion resistance (correct)

AAAC conductors are preferred for high-voltage transmission due to their high tensile strength.

False (B)

What alloy is used to make AAAC conductors?

Aluminium-Magnesium-Silicon alloy

The main purpose of using galvanized steel in ACSR conductors is to prevent ______.

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

Match the following types of conductors with their primary characteristics:

<p>AAC = Limited use in transmission due to poor strength AAAC = Good conductivity with better mechanical strength ACSR = Increased tensile strength with galvanized steel core Bundled conductors = Improved heat dissipation and reduced corona losses</p> Signup and view all the answers

What is the typical configuration for bundled conductors in 220 kV lines?

<p>Two-conductor bundles (B)</p> Signup and view all the answers

Bundling conductors helps to reduce the inductance in high-voltage lines.

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

What is the primary reason for increasing the surface area of conductors by bundling?

<p>Increasing heat dissipation</p> Signup and view all the answers

What happens to the inductance of a transmission line if the spacing between the conductors increases?

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

The inductance of a transmission line is independent of the radius of the conductors.

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

What is the formula for the total inductance of a two-wire transmission line?

<p>l = (μ / (2π)) * (1/D + ln(4r/D))</p> Signup and view all the answers

The inductive reactance of a transmission line is denoted as _____ and depends on inductance and frequency.

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

Match the terms with their definitions:

<p>Inductance = Opposition to change of current Inductive Reactance = Opposition to alternating current Frequency = Number of cycles per second Power System = Network for electrical energy distribution</p> Signup and view all the answers

What is the main factor that affects the series inductive reactance of a transmission line?

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

The length of the transmission line has no effect on the total series inductive reactance.

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

What is the relationship between the radius of the conductors and the inductance of the line?

<p>The greater the radius of the conductors, the lower the inductance of the line.</p> Signup and view all the answers

What is the value of the total shunt admittance Yse for the given transmission line?

<p>j 7.684 x 10^-5 S (C)</p> Signup and view all the answers

The shunt capacitive reactance is represented as a positive value.

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

What type of conductor is used in the example for calculating the inductance and capacitance of the transmission line?

<p>Composite (stranded) conductor</p> Signup and view all the answers

The distance between two conductors in a balanced three-phase transmission line is represented by D = ______.

<p>5m</p> Signup and view all the answers

Which formula is used to calculate the inductance of each conductor?

<p>$λa = \frac{µ_0}{2π} [ia \ln(\frac{1}{r'}) + ia \ln(\frac{1}{D})]$ (B)</p> Signup and view all the answers

Match each term with its correct definition:

<p>Shunt admittance = Total admittance per unit length of a transmission line Inductance = Opposition to the change of current in a conductor Capacitance = Ability of a conductor to store electronic charge Reactance = Resistance experienced by the flow of alternating current</p> Signup and view all the answers

A balanced transmission line assumes equal currents in all three phases.

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

The resistive part of the shunt admittance is represented as ______.

<p>0</p> Signup and view all the answers

What is the impact of conductor bundling on inductance?

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

The total reactance for a 5-mile line calculated is 3.79 Ω.

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

What is the typical number of conductors for 500 kV lines?

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

The formula for calculating inductance per phase is La = ln(________) where the spacing is symmetric.

<p>2πr'</p> Signup and view all the answers

Match the following spacing configurations with their associated line types:

<p>Symmetric spacing = No mutual inductance Asymmetric spacing = Mutual coupling Conductor bundling = Increased capacity Horizontal phase spacing = 10 meters</p> Signup and view all the answers

What is the new inductance per meter when using four conductors in a square bundle with the given parameters?

<p>7.46 × 10−7 H/m (C)</p> Signup and view all the answers

The conductor radius used in the calculations is 0.5 cm.

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

What is the reactance formula used to calculate Aa for the three-phase line?

<p>Xa = 2π × 60 × La</p> Signup and view all the answers

What is the series resistance per kilometer of the transmission line?

<p>0.0225 Ω/km (A)</p> Signup and view all the answers

The series inductance of the transmission line is irrelevant for impedance calculations.

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

What is the resistivity of the line at 200°C?

<p>2.83 × 10^{-8} Ω-m</p> Signup and view all the answers

The formula for series inductance per kilometer is __________.

<p>l = µ(1/4r + ln(D/4r)) × 1000</p> Signup and view all the answers

What is the radius of each conductor in meters?

<p>0.02 m (D)</p> Signup and view all the answers

Match the following components with their respective formulas:

<p>Series Resistance = ρl/A Series Inductance = µ(1/4r + ln(D/4r)) Total Impedance = Z = R + jX Area = πr^2</p> Signup and view all the answers

What frequency does the transmission line operate at?

<p>60 Hz</p> Signup and view all the answers

The total length of the transmission line is __________.

<p>30 km</p> Signup and view all the answers

What is the inductive reactance per mile for a Partridge conductor at 20 ft spacing operating at 60 Hz?

<p>0.8285 Ω/mile (C)</p> Signup and view all the answers

The capacitive reactance between the conductor and the neutral can be determined from the given information.

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

What is the GMR value for the Partridge conductor?

<p>0.0217 ft</p> Signup and view all the answers

The inductive reactance for the entire length of the ACSR Drake line is __________.

<p>To be calculated based on inductive reactance per mile and line length.</p> Signup and view all the answers

Match the following reactances to their respective terms:

<p>Inductive Reactance per Mile = 0.8285 Ω/mile Capacitive Reactance to Neutral = Value not provided Charging Current = To be calculated Charging Reactive Power = To be calculated</p> Signup and view all the answers

What is the calculated inductive reactance for one mile of the ACSR Drake line?

<p>All of the above (D)</p> Signup and view all the answers

The spacing factor is irrelevant to the calculation of inductive reactance.

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

What is the normal operating voltage mentioned for the three-phase line?

<p>220 kV</p> Signup and view all the answers

Flashcards

AAC

Aluminum Alloy Conductor; a type of conductor with good conductivity but relatively low strength, suitable for urban distribution lines with short spans.

AAAC

All Aluminium Alloy Conductor; a high-strength aluminium alloy conductor with good conductivity and lighter weight than ACSR for equal strength, suitable for distribution lines, especially in coastal areas.

ACSR

Aluminum Conductor Steel Reinforced; a stranded conductor with a central core of galvanized steel wires for high tensile strength, used in high-voltage transmission lines.

Bundled Conductors

Multiple wires grouped closely together on transmission lines; used to increase heat dissipation, reduce corona losses, and decrease inductance, and increase current capacity due to decreased skin effect.

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Conductor Bundling

Grouping multiple conductors (wires) on transmission lines.

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Transmission Lines

Electrical lines used to efficiently transport high voltage transmissions across a long distance

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Distribution Lines

Low voltage electrical lines that transmit electricity from transmission lines closer to the place of use (e.g., residential areas).

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Shunt admittance (Ysh)

A measure of how easily current flows through a transmission line's shunt capacitance. It's expressed in Siemens (S).

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Shunt capacitive reactance (Zsh)

The opposition to current flow through the shunt capacitance of a transmission line, expressed in ohms (Ω).

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Transmission line inductance

Measures the opposition to changes in current in a transmission line based magnetic field interactions, measured in Henries (H).

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Transmission line capacitance

Measures the ability of a transmission line to store electrical energy through an electric field between the conductors, measured in Farads(F)

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Two-conductor line inductance calculation

Calculating inductance in a two-wire system, considering the cancellation of magnetic fields due to current flowing in opposite directions.

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Balanced 3φ transmission line

A 3-phase transmission line where the currents in the three conductors are equal in magnitude and opposite in phase.

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Series Resistance

Resistance of a transmission line to current flow along its length

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Resistance per kilometer

Resistance of a transmission line per kilometer (a unit length).

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Series Inductance

Measure of a transmission line's tendency to oppose changes in current.

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Inductance per kilometer

Inductance of a transmission line per kilometer (a unit length).

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Transmission Line Resistance Calculation

Resistance formula (R=ρl/A) , where ρ = resistivity, l = length, and A = cross-sectional area.

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Transmission Line Inductance Calculation

Formula for calculating inductance which often involves factors like distance between conductors and ln function

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Conductor Bundling

Using multiple conductors per phase in high-voltage transmission lines to increase capacity.

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Bundle Inductance

The inductance of a transmission line with multiple conductors per phase, calculated accounting for the bundled conductors' spacing.

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Inductance (La)

The ability of a conductor to store energy in a magnetic field when current flows through it.

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Reactance (Xa)

The opposition to alternating current(AC) in an electrical circuit.

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Mutual Inductance

The effect where the magnetic field of one conductor induces a voltage in another.

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Symmetric Conductor Spacing

Conductors positioned equidistantly in 3-phase transmission lines in a symmetrical pattern.

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Phase Spacing

The distance between phases in a 3-phase electrical circuit.

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3-phase line inductance

Inductance per phase of a balanced three-phase transmission line.

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Bundled conductors

Multiple conductors combined into a single phase.

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Inductive Reactance (single-phase)

Opposition to the change of current in a single-phase transmission line due to its inductance.

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Capacitive Reactance (single-phase)

Opposition to the change of voltage in a single-phase transmission line, associated with the capacitance of the conductors.

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GMR (Geometric Mean Radius)

A calculated radius representing the equivalent radius of a conductor bundle for inductance calculations.

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Spacing Factor (Xd)

A correction factor applied to the inductive reactance due to the spacing between conductors.

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Inductive Reactance per mile (single-phase)

The inductive reactance per unit length of a single-phase transmission line.

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Capacitive Reactance to Neutral (per mile)

Resistance to the change in voltage between a single conductor and the neutral point for a single mile of line.

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Charging Current

Current flowing through a transmission line due solely to its capacitance, not the load current.

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Charging Reactive Power

Reactive power associated with the charging current in a transmission line.

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ACSR Drake

A type of aluminum conductor, reinforced with steel, used in high-voltage three-phase transmission lines.

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Three-phase line

An electrical transmission system using three conductors to carry power.

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Transmission Line Inductance

The opposition to changes in current in a transmission line, caused by magnetic field interactions.

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Two-Wire Transmission Line Inductance

The total inductance per unit length of a two-wire transmission line, calculated considering both internal and external inductance.

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Inductance Formula (two-wire)

µ/π * (1/4 + ln(D/r)) , where µ is permeability, r the radius, D the distance between conductors

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Inductive Reactance

The opposition to alternating current in a transmission line due to inductance.

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Inductive Reactance Formula

ωL, where ω is angular frequency and L is inductance.

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Bundle Conductors

Multiple conductors bundled together in a transmission line.

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Bundle Conductor Wind Loading

Increased wind resistance from a transmission line using multiple wire bundles.

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Transmission Line Spacing Effect on Inductance

Greater spacing between phases of a transmission line, leads to greater inductance.

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Conductor Radius Effect on Inductance

Larger conductor radius decreases inductance in a transmission line.

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Study Notes

Power Generation and Transmission

  • Types of Conductors:
    • Copper: Strong, good conductivity, high current density, durable, high scrap value
    • Aluminum: Cheaper than copper, lighter, second-best conductivity, lower tensile strength, prone to damage from heat
    • Steel: High tensile strength, but low conductivity, used for ground wires
    • Steel-cored Aluminum: Strength of steel and conductivity of aluminum.
    • AAC (All Aluminum Conductor): Good conductivity, but lower strength.
    • AAAC (All Aluminum Alloy Conductor): Higher strength and conductivity than AAC, used for rural distribution
    • ACSR (Aluminum Conductor Steel Reinforced): Strength of steel and conductivity of aluminum, used for high-voltage transmission
    • ACAR (Aluminum Conductor Alloy Reinforced): Alloy conductors, mainly used in coastal areas for better corrosion resistance

Conductor Selection Considerations

  • High Tensile Strength: Material in conductors must handle high loads to prevent sagging in long spans.
  • Low Resistivity: Reducing power losses and voltage drop, which saves money and energy.
  • Low Cost: Economic conductor materials.
  • Low Corrosion: Stable conductors prevent degradation and maintain reliability.
  • Low Skin Effect & Corona Losses: Specific conductor structure minimizes losses related to high voltages, such as skin effect, this improves efficiency and reduces cost

Bundling of Conductors

  • Heat Dissipation: Increases surface area aiding efficient heat dissipation.
  • Reducing Corona Losses: Bundling decreases corona discharge, enhancing efficiency and reducing energy loss in high-voltage lines
  • Reducing Inductance: Fewer currents running parallel to each other reduce inductance, improving performance
  • Increasing Current Capacity: Bundled conductors lower the overall effect of the skin effect which increases current capacity, improving efficiency.
  • 220 kV lines: Typically use two conductor bundles
  • 380 kV lines: Typically use three or more conductor bundles

Inductance of Single-Phase Two-Wire Transmission Line

  • Internal inductance + external inductance between the conductor and the surrounding space
  • Permeability is the degree to which a material permits the formation of magnetic flux.
  • Inductance (l) is proportional to the permeability (µ)
  • Inductance is inversely proportional to the natural logarithm of the radius (r),
  • Inductance is proportional to the separation distance (D).
  • The total inductance of the other wire is the same.
  • The total inductance of a two-wire transmission line is proportional to the (ln(D)).

Inductance of a Transmission Line

  • Spacing between phases of transmission line increases inductance.
  • Increased radius of conductors in a transmission line decreases inductance.

Capacitance of a Single-Phase Two-Wire Transmission Line

  • Capacitance (C) is directly proportional to the permeability (ɛ)
  • Capacitance is inversely proportional to the natural logarithm of the radius (r),
  • Capacitance is inversely proportional to the separation distance (D). The capacitance to ground is one half the capacitance between conductors.

Capacitance in a Transmission Line

  • The greater the spacing between the phases of a transmission line, the lower the capacitance of the line.
  • The greater the radius of the conductors in a transmission line, higher the capacitance of the line.

Shunt Capacitive Admittance

  • Shunt capacitive admittance depends on capacitance and power system frequency.
  • Total shunt capacitive admittance is proportional to the frequency (f) and capacitance per unit length (c).
  • Total shunt capacitive admittance is directly proportional to the length of the line (d).
  • Capacitive reactance is the reciprocal of the admittance.

Example Calculations

(Specific calculation details are included in the pages of the notes, which are provided in the text you uploaded)

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