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Questions and Answers
What happens to the capacitance of a transmission line when the spacing between the phases increases?
What happens to the capacitance of a transmission line when the spacing between the phases increases?
The radius of the conductors in a transmission line has no effect on the capacitance of the line.
The radius of the conductors in a transmission line has no effect on the capacitance of the line.
False
What is the formula for capacitive reactance?
What is the formula for capacitive reactance?
ZC = -j/(2πfC)
The shunt capacitive admittance of a transmission line is given by the formula ____ × j 2π f.
The shunt capacitive admittance of a transmission line is given by the formula ____ × j 2π f.
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Match the following concepts with their corresponding descriptions:
Match the following concepts with their corresponding descriptions:
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What is the inductance of the line for a single-phase Partridge conductor with 20 ft spacing?
What is the inductance of the line for a single-phase Partridge conductor with 20 ft spacing?
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The spacing factor for a 20 ft spacing is higher than the inductive reactance at 1 ft spacing.
The spacing factor for a 20 ft spacing is higher than the inductive reactance at 1 ft spacing.
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What is the GMR for a Partridge conductor?
What is the GMR for a Partridge conductor?
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The capacitive reactance for one mile of a single-phase line is measured in ______.
The capacitive reactance for one mile of a single-phase line is measured in ______.
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Which conductor type is used in the example for both single-phase and three-phase lines?
Which conductor type is used in the example for both single-phase and three-phase lines?
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Inductive reactance increases with the spacing between conductors.
Inductive reactance increases with the spacing between conductors.
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How is the total inductive reactance for a 175-mile three-phase line calculated?
How is the total inductive reactance for a 175-mile three-phase line calculated?
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Match the following properties to their corresponding values for the Partridge conductor:
Match the following properties to their corresponding values for the Partridge conductor:
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What is the series impedance per kilometer of the transmission line?
What is the series impedance per kilometer of the transmission line?
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The inductive reactance Xd is defined as the inductive reactance at a certain spacing.
The inductive reactance Xd is defined as the inductive reactance at a certain spacing.
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What does GMR represent in transmission line calculations?
What does GMR represent in transmission line calculations?
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The formula for capacitive reactance, given the values from the table, includes a factor of 2πf and a term for _______.
The formula for capacitive reactance, given the values from the table, includes a factor of 2πf and a term for _______.
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Match the reactance calculation with their corresponding parameters:
Match the reactance calculation with their corresponding parameters:
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What is the value of the inductive reactance Xa for a single-phase line at 60 Hz with 1 ft spacing?
What is the value of the inductive reactance Xa for a single-phase line at 60 Hz with 1 ft spacing?
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In the context of transmission lines, what does a larger spacing between conductors typically lead to?
In the context of transmission lines, what does a larger spacing between conductors typically lead to?
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If both GMR and GMD are in feet, Xa represents the inductive reactance at 6 ft spacing.
If both GMR and GMD are in feet, Xa represents the inductive reactance at 6 ft spacing.
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Study Notes
Power Transmission Line Conductors
- Different conductor types are used in power transmission lines, including:
- All Aluminium Conductor (AAC)
- All Aluminium Alloy Conductor (AAAC)
- Aluminium Conductor, Steel Reinforced (ACSR)
- Aluminium Conductor, Alloy Reinforced (ACAR)
- Conductor selection is a compromise balancing several factors:
- High tensile strength is needed to withstand high breaking loads and long spans between towers.
- Low resistivity to reduce power losses and voltage drop.
- Low cost for installation and maintenance and a long life.
- Low corrosion resistance.
- Low skin effect and corona losses to minimize any extra losses.
Conductor Materials (Copper, Aluminum, Steel)
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Copper:
- High conductivity, making it suitable for high current density.
- Strongest compared to other metals, making it ideal for withstanding wind pressure and sag.
- Homogeneous with consistent properties throughout.
- Durable.
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Aluminum:
- Second highest conductivity, but at a lower price.
- Lighter in weight, which reduces sag and the need for stronger supports.
- Lower tensile strength than copper, needing reinforcement
- More prone to damage from short circuits or corrosion.
-
Steel and Steel-Cored Aluminum:
- High tensile strength, suitable for reinforcing conductors that carry high tension.
- Lowest conductivity, used primarily for supporting conductors to increase overall tensile strength, not for carrying current directly.
- Prone to rust and reduce efficiency when exposed to damp atmospheres.
Types of Conductors in Power Transmission
- AAC: All Aluminum Conductor. Mostly used for short spans in LV distribution systems. Relatively poor strength.
- AAAC: All Aluminum Alloy Conductor. Higher strength and conductivity used for distribution lines.
- ACSR: Aluminum Conductor, Steel Reinforced. Commonly used high-voltage transmission lines, balancing strength and weight. Stronger than AAC.
- ACAR: Aluminum Conductor, Alloy Reinforced. Higher strength than ACSR, often used in certain applications.
Bundling of Conductors
- Bundling conductors, especially in high-voltage, high-capacity lines, is used for several reasons:
- Increases heat dissipation because of larger surface area.
- Reduces wind loading.
- Reduces inductance.
- Increases current-carrying capacity due to reduced skin effect.
Inductance of a Transmission Line
- The inductance of a transmission line depends on spacing and conductor size.
- Greater spacing means greater inductance.
- Greater conductor radius means lower inductance.
Capacitance of a transmission Line
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The capacitance of a transmission line depends on spacing and conductor size.
- Greater spacing means lower capacitance.
- Greater conductor radius means higher capacitance.
-
Calculating total capacitance and inductance is crucial when designing a power transmission system.
Inductive Reactance of A Line
- The inductive reactance of a line is directly proportional to the frequency and length of the line.
- The greater the frequency or length of the line, the greater the inductive reactance.
Example Calculations
- Example calculations are provided, demonstrating how to calculate series resistance, inductance, capacitance, impedance, and admittance.
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Description
This quiz covers the various types of conductors used in power transmission lines, including their materials and characteristics. Explore the advantages and trade-offs associated with conductor selection, such as tensile strength and resistivity. Ideal for students and professionals interested in electrical engineering.
