Name: how transmission lines lose energy
Uploaded: 2024-11-21T14:54:23.000Z
Duration: 1 min 25 s
Channel: JoVE

A conductor&#39;s DC resistance at a specific temperature depends on its resistivity, length, and cross-sectional area.
Resistivity varies by conductor metal, with annealed copper as the standard for measurement.
Hard-drawn aluminum&#39;s resistivity at 20&#186;C&#160;is 61% of copper&#39;s conductivity.
Factors like spiraling, temperature, frequency, and current magnitude impact resistance. Spiraling in stranded conductors increases their length and DC resistance by 1-2%.
Resistivity changes linearly with temperatures.
AC resistance is determined by real power loss and rms current.
The Skin effect increases with frequency, causing a rise in AC resistance, while for magnetic conductors, resistance depends on the current magnitude.
Conductance, accounting for real power loss between conductors or to the ground, is primarily due to insulator leakage currents and corona effects. Though these are minor compared to conductor loss.
Insulator leakage current is affected by contaminants and moisture.
Corona, caused by high electric field strength ionizing air, depends on weather conditions and conductor surface irregularities.

resistance and conductance

Resistance and Conductance

A conductor&#39;s DC resistance at a given temperature is influenced by its resistivity, length, and cross-sectional area. Resistivity is an inherent property of the conductor material, with annealed copper serving as the international standard for measurement. For instance, the resistivity of hard-drawn aluminum at 20 degrees Celsius is 61% of the standard conductivity of annealed copper.
Various factors impact the resistance of a conductor. Spiraling in stranded conductors increases their length and, consequently, their DC resistance by 1-2%. Additionally, resistivity varies linearly with temperature over normal operating ranges. Frequency and current magnitude also play crucial roles; the skin effect, which intensifies with frequency, increases AC resistance. In magnetic conductors, resistance is further influenced by the current magnitude.
AC, or effective resistance, is determined by the real power loss and the root mean square (rms) conductor current. The skin effect becomes significant at higher frequencies, causing current to concentrate near the conductor&#39;s surface, thereby increasing AC resistance. This effect is more pronounced in conductors with magnetic properties, where resistance varies with the current&#39;s magnitude.
Conductance, associated with real power loss between conductors or to the ground, is primarily due to insulator leakage currents and corona effects. Although these losses are relatively minor compared to conductor losses, they are significant in the overall assessment of a transmission line&#39;s efficiency. Insulator leakage current is influenced by accumulated contaminants and meteorological conditions, particularly moisture.
Corona occurs when the electric field around a conductor ionizes the surrounding air, leading to conduction. Corona loss is contingent upon weather conditions and the conductor&#39;s surface irregularities, which can exacerbate ionization effects. Understanding these factors is essential for optimizing transmission line performance and minimizing energy losses.

A conductor&#39;s DC resistance at a specific temperature depends on its resistivity, length, and cross-sectional area.
Resistivity varies by conductor ...

Education

JoVE Core

Electrical Engineering

Unit 1

Transmission Line Parameters

KEY TERMS AND CONCEPTS

how transmission lines lose energy

Transmission lines lose energy through resistance and conductance. DC resistance depends on a conductor’s resistivity, length, and cross-sectional area. Resistivity is a material property, and annealed copper is the international standard used for measurement.

Material choice and conductor shape both matter. Hard-drawn aluminum at 20 degrees Celsius has a resistivity equal to 61% of the standard conductivity of annealed copper. Stranded conductors also gain a little extra resistance because spiraling makes the path longer. This increase is usually about 1% to 2%.

Temperature changes resistance as well. Over normal operating ranges, resistivity rises or falls in a linear way with temperature. AC resistance, or effective resistance, also depends on frequency and current magnitude. At higher frequencies, the skin effect pushes current toward the outside of the conductor and increases AC resistance.

Magnetic conductors show an added effect. Their resistance can change with the size of the current. AC resistance is found from real power loss and the rms, or root mean square, conductor current. Conductance describes real power loss between conductors or to the ground, and it mainly comes from insulator leakage currents and corona.

These losses are usually small compared with conductor losses, but they still matter for transmission line efficiency. Leakage current increases when dirt and other contaminants build up on insulators, and moisture from weather makes this worse. Corona occurs when the electric field around a conductor ionizes the air. Its loss depends on weather and on surface roughness that can make ionization easier.

How Transmission Lines Lose Energy

transmission line design considerations

Overhead Power Line Materials and Safety

Overhead transmission lines rely on the right materials, insulation, and support hardware to move electricity safely and efficiently. Aluminum is now the preferred conductor material because it is abundant and cost-effective. Copper was used more often in the past, but aluminum has become the common choice for modern lines. The most widely used conductor is aluminum conductor, steel-reinforced, or ACSR. It uses aluminum strands around a steel core for added strength. Other conductor types...

Transmission lines lose energy through resistance and conductance. DC resistance depends on a conductor’s resistivity, length, and cross-sectional area. Resistivity is a material property, and annealed copper is the international standard used for measurement. Material choice and conductor shape both matter. Hard-drawn aluminum at 20 degrees Celsius has a resistivity equal to 61% of the standard conductivity of annealed copper. Stranded conductors also gain a little extra resistance because...

inductance: solid cylindrical conductor

Magnetic Flux Linkage in Solid Conductors

Magnetic flux linkage in a solid cylindrical conductor is found by combining the field inside the wire with the field around it. The method uses a 1-meter section of a non-magnetic conductor with radius r. It also assumes the current is spread uniformly and ignores end effects. Inside the conductor, Ampere's law is used to find the magnetic field intensity H. The field is concentric and constant within the conductor. From H, the magnetic flux density B inside the wire is calculated. The...

inductance: single-phase and three-phase line

inductance-single-phase-and-three-phase-line

Transmission Line Inductance in Power Cables

Transmission line inductance helps explain how current-carrying conductors behave in power systems. It is especially important when studying single-phase two-wire lines and three-phase three-wire lines with equal phase spacing. These line types are common models for efficient transmission design and operation. A single-phase line uses two solid cylindrical conductors, labeled x and y. Each conductor carries a phasor current, ix and iy, and the sum of these currents is zero. The total flux...

series impedances: three-phase line

Three-Phase Line Impedance Matrix

Three-phase line impedance matrix calculations describe how resistance and inductive reactance behave in an overhead power line. The model includes three phase conductors and multiple neutral conductors that are grounded at regular intervals. It also accounts for unbalanced phase currents, which can send return current through the neutral wires and the earth along the lowest-impedance path. Kirchhoff’s laws are used to build an integro-differential equation for the conductor network. To make...

capacitance: single-phase and three-phase line

capacitance-single-phase-and-three-phase-line

Transmission Line Capacitance in Power Systems

Transmission line capacitance affects how power lines store charge and behave in electrical power systems. It is an important part of line modeling because it helps describe efficient operation. For a single-phase line, the key idea is the charge on the conductors and the voltage between them. A single-phase transmission line uses two wires with equal spacing. One conductor carries a uniform positive charge, and the other carries an equal negative charge. From the voltage between the...

shunt admittances

Image Method for Line Capacitance

Image conductors help model line capacitance in transmission lines above Earth. A uniformly charged conductor induces an equal and opposite charge on the ground. This creates electric field lines between the conductor and the Earth. The method of images replaces the Earth with a matching conductor placed symmetrically below the line. The image conductor has the same radius and the same charge magnitude as the original conductor. That setup keeps the electric field and voltage above the Earth...

key terms and concepts

Explore how resistance and conductance affect transmission line energy loss, including temperature, skin effect, leakage current, and corona.

How Transmission Lines Lose Energy | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

How Transmission Lines Lose Energy

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