Name: reducing power loss in three-phase lines
Uploaded: 2024-07-08T13:19:58.000Z
Duration: 1 min 10 s
Channel: JoVE

時間領域で表される平衡型3線式Y-Y回路を考えてみて、これは位相ごとの等価回路に変換できます。
最初にライン電流が決定され、次に負荷の位相電圧が決定されます。
次に、ソースによって供給される電力は、正弦波位相電圧とライン電流の実効値を使用して決定されます。
次に、ライン電流と負荷抵抗を使用して、負荷に供給される電力を計算します。
ラインで失われる電力は、ライン電流とライン抵抗を使用して取得されます。
次に、三相電源によって供給される総電力、三相負荷によって受信される総電力、およびラインで失われる総電力が決定されます。
ラインで電力が失われる割合が高く、ライン電流を最小限に抑えることで電力を削減できます。
ただし、これにより負荷電流が減少し、負荷に供給される電力が減少します。
負荷電流に影響を与えずにライン電流を減らす方法の1つは、三相回路にトランスを導入することです。

ライン損失

電源と負荷の接続には、Y 字型 (スター型) とデルタ型があります。ラインと位相の電圧と電流の関係は、構成によって異なります。電源が電力を供給している場合、電力はワイヤを介して負荷に伝送されますが、この伝送中に一部の電力がワイヤに吸収され、ライン損失が発生します。

ライン損失は、バランスの取れた 3 相回路での電力供給効率に影響します。このような回路の対称性により、1 つの位相のみを考慮できるため、分析が簡素化されます。位相ごとの等価回路は、ライン損失などのさまざまなパラメーターの計算に役立ちます
電力損失の計算:
負荷の各位相に供給される電力は、位相電流の 2 乗と位相負荷抵抗の積です。
ライン損失の計算:
各ワイヤのライン損失は、ライン電流の大きさの 2 乗にラインの抵抗を掛けて計算されます。
平衡型三相システムの場合、この計算に 3 を掛けて (各相に 1 つずつ)、総電力損失を算出します。ラインの抵抗は、素材の抵抗率とラインの長さに正比例し、導体の断面積に反比例します。つまり、ライン損失は導体の長さに正比例し、導体の断面積に反比例します。電力会社は、断面積の大きい導体を使用してライン損失を最小限に抑え、より高い電圧で電力を伝送します。これにより、同じ量の電力でより低い電流が可能になります。これは、電力が電圧と電流の積であるためであり、特定の電力レベルでは、電圧を上げると電流が減少し、ライン損失が削減されます。

時間領域で表される平衡型3線式Y-Y回路を考えてみて、これは位相ごとの等価回路に変換できます。
まず、...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Three-Phase Circuits

三相回路

KEY TERMS AND CONCEPTS

主要用語および概念

Line Loss

reducing power loss in three-phase lines

Three-phase power lines can lose energy as electricity travels from the source to the load. This line loss affects how efficiently power reaches the load. In balanced three-phase circuits, the symmetry makes the analysis easier because one phase can represent the whole system.

The source-load connection can use wye, also called star, or delta configurations. These setups change the relationship between line voltage, phase voltage, line current, and phase current. A per-phase equivalent circuit helps calculate the power delivered to the load and the power lost in the lines.

For each phase of the load, the delivered power depends on the square of the phase current and the phase load resistance. The power lost in one wire is found from the square of the line current multiplied by the resistance of that line. For a balanced three-phase system, the total line loss is three times the loss in one phase.

Line resistance depends on the material resistivity, the length of the conductor, and its cross-sectional area. As the line gets longer, resistance and line loss increase. A larger cross-sectional area lowers resistance and helps reduce loss. Power companies use larger conductors and higher transmission voltages to keep current lower for the same power level, which reduces line loss.

Reducing Power Loss in Three-Phase Lines

three-phase circuits

How Three-Phase Power Delivers Electricity

Three-phase power is a major part of AC power distribution, especially where steady and efficient electricity delivery is needed. AC systems are grouped into single-phase, two-phase, and three-phase systems. These categories help describe how power moves from the source to the load. Single-phase circuits are common in homes. They usually use a two-wire system that connects one AC source to loads. These circuits can supply everyday appliances such as lamps, televisions, and microwaves at 120 V...

generation of three-phase voltage

Three-Phase AC Generator Windings

A three-phase AC generator uses rotating magnet windings and a stationary stator to make three-phase voltage. The rotor carries a magnet that spins inside the stator. The stator holds the three-phase winding, and mutual induction creates the voltage. The stator windings are spread evenly around the inside of the stator. They are placed 120 electrical degrees apart. These windings consist of three separate coils, or groups of coils, called phases. The phases can be connected in a Y, or star,...

three-phase voltages

Three-Phase Power Connections

Three-phase power connections use balanced voltages that are equal in magnitude and separated by 120 degrees. A three-phase generator produces these voltages, and the balance helps reduce power loss while keeping energy delivery steady to connected loads. Three-phase sources can be arranged in either wye or delta form. The loads connected to the system can also use wye or delta. This flexibility gives control over how the system is designed and managed. In a wye connection, one end of each...

the y-to-y circuit

Balanced Wye-to-Wye Neutral Current

A balanced wye-to-wye circuit uses three wye-connected sinusoidal voltage sources and three wye-connected loads. A neutral wire links the neutral node of the source to the neutral node of the load. The load impedance is connected across each phase of the load. The source and load can be connected in either a four-wire or a three-wire arrangement. A three-phase system is balanced when each phase has the same load. In that case, the current flow and phase angle are uniform across the system. If...

the y-to-delta circuit

Wye Source and Delta Load Currents

A balanced wye source and delta load form a common three-phase circuit with no neutral line connection. The source is Y-connected, and the load is delta-connected. To analyze the circuit, the first step is to assume a positive phase sequence. These phase voltages are then used to find the line voltages that appear across the delta load impedances. In the wye source, the phase voltages are V an, V bn, and V cn. In the delta load, the line voltages are V ab, V bc, and V ca. These line voltages...

the delta-to-delta circuit

Balanced Delta-Delta Power Circuit

A balanced delta-delta power circuit uses a delta-connected source and a delta-connected load. The two deltas form a closed loop that creates three separate phases. In this setup, the phase voltages are the same as the line voltages. If the source is in positive sequence, the phase voltages can be written directly, and no neutral wire is needed. The delta-connected load current is found by dividing the phase voltage by the impedance of each phase. For line current, Kirchhoff’s Current Law...

the delta-to-y circuit

Delta-Wye Source and Load Connections

A balanced delta-wye circuit connects a delta-connected source to a wye-connected load. In this setup, the phase voltage of the delta source equals the line voltage of the wye load. The source also sets the line currents that flow into the load. For a balanced system, the phase difference between currents makes it possible to find one line current from the other by using the positive sequence of phases. In the wye-connected load, each phase current equals the line current from the delta source.

power in a three-phase circuit

Balanced Three-Phase Power Calculation

Balanced three-phase power calculation depends on the wye and delta connections used in the circuit. A wye, or star, configuration can use three wires or four wires. A delta configuration connects the components in a closed loop. These connection types change how voltages and currents are arranged, but both are used in three-phase systems. In a balanced three-phase system, instantaneous power is the power at one exact moment. Even though the power in each phase changes over time, the total...

power distribution in three-phase and single phase circuits

power-distribution-in-three-phase-and-single-phase-circuits

Single-Phase vs. Three-Phase Power Loss

Single-phase and three-phase circuits distribute electrical power in different ways. Single-phase power is common in homes, while balanced three-phase power is widely used in industrial settings with heavy machinery. Both systems deliver energy, but their current flow and wire needs are not the same. A single-phase circuit usually uses a two-wire system. The current depends on the power absorbed by the load and the line voltage. Because wire loss from resistance follows the square of the...

line loss

Three-phase power lines can lose energy as electricity travels from the source to the load. This line loss affects how efficiently power reaches the load. In balanced three-phase circuits, the symmetry makes the analysis easier because one phase can represent the whole system. The source-load connection can use wye, also called star, or delta configurations. These setups change the relationship between line voltage, phase voltage, line current, and phase current. A per-phase equivalent circuit...

reducing line loss

Cutting Heat Loss in Three-Phase Lines

Three-phase power systems can lose energy as heat in transmission lines because the wires have resistance. This line loss becomes important when electricity travels over a distance. A common solution is to use transformers to change the voltage and current in the system. The setup uses two three-phase transformers. A step-up transformer is placed at the source, and a step-down transformer is placed at the load. Raising the voltage at the source lowers the current in the transmission lines, and...

key terms and concepts

Learn how balanced three-phase circuits, wye and delta connections, and conductor size affect line loss, power delivery, and transmission efficiency.

Reducing Power Loss in Three-Phase Lines | 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

Reducing Power Loss in Three-Phase Lines

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