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

特定の温度での導体の直流抵抗は、その抵抗率、長さ、および断面積によって異なります。
抵抗率は導体金属によって異なり、焼きなまし銅が測定の基準となります。
20ºCでの硬質アルミニウムの抵抗率は、銅の導電率の61%です。
スパイラル、温度、周波数、電流の大きさなどの耐衝撃性などの要因。撚り線導体のスパイラル化により、導体の長さとDC抵抗が1〜2%増加します。
抵抗率は温度に比例して変化します。
AC抵抗は、実際の電力損失とrms電流によって決まります。
表皮効果は周波数とともに増加し、AC抵抗の上昇を引き起こしますが、磁気導体の場合、抵抗は電流の大きさに依存します。
コンダクタンスは、導体間またはグランドへの実際の電力損失を考慮し、主に絶縁体の漏れ電流とコロナ効果によるものです。これらは導体の損失に比べれば軽微ですが。
絶縁体の漏れ電流は、汚染物質や湿気の影響を受けます。
コロナは、電界強度の高い電離空気によって引き起こされ、気象条件や導体表面の凹凸に依存します。

抵抗と伝導

Resistance and Conductance

特定の温度における導体の直流 (DC) 抵抗は、その抵抗率、長さ、断面積によって左右されます。抵抗率は導体材料固有の特性であり、焼鈍銅が測定の国際標準となっています。たとえば、20 ℃ での硬質アルミニウムの抵抗率は、焼鈍銅の標準導電率の 61% です。 
導体の抵抗にはさまざまな要因が影響します。撚り線をらせん状にすると導体の長さが長くなり、その結果 DC 抵抗が 1 ～ 2% 増加します。さらに、抵抗率は通常の動作範囲で温度に比例して変化します。周波数と電流値も重要な役割を果たします。周波数とともに強くなる表皮効果により、AC 抵抗が増加します。磁性導体では、抵抗は電流値によってさらに影響を受けます。 
AC または有効抵抗は、実際の電力損失と導体電流の実効値 (rms) によって決まります。表皮効果は周波数が高くなると顕著になり、導体の表面近くに電流が集中するため、AC 抵抗が増加します。この効果は、抵抗が電流の大きさに応じて変化する磁性を持つ導体でより顕著になります。 
導体間または地面への実際の電力損失に関連するコンダクタンスは、主に絶縁体漏れ電流とコロナ効果によるものです。これらの損失は導体損失に比べると比較的小さいものですが、伝送線路の効率の全体的な評価においては重要です。絶縁体漏れ電流は、蓄積された汚染物質や気象条件、特に湿気の影響を受けます。 
コロナは、導体の周囲の電界が周囲の空気をイオン化して伝導を引き起こすときに発生します。コロナ損失は気象条件と導体の表面の凹凸に左右され、イオン化の影響を悪化させる可能性があります。これらの要因を理解することは、伝送ラインのパフォーマンスを最適化し、電力損失を最小限に抑えるために不可欠です。

特定の温度での導体の直流抵抗は、その抵抗率、長さ、および断面積によって異なります。
抵抗率は導体によって異なります...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Transmission Line Parameters

伝送線路パラメータ

KEY TERMS AND CONCEPTS

主要用語と概念

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...

resistance and conductance

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 電気工学 は、電気回路の基本概念と回路解析テクニックを網羅したアニメーションビデオシリーズです。オペアンプと回路変換および 1 次・ 2 次回路の概念を網羅しています。実験を撮影した実写動画では、設計例や現代社会での応用が含まれており、複雑な概念も分かりやすく学習いただけます。

electrical engineering

How Transmission Lines Lose Energy

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