Name: how three-phase power delivers electricity
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 22 s
Channel: JoVE

一般に、AC配電システムは、単相、二相、または三相に分類されます。
単相回路には、2線式システムを介して負荷に接続された単一のソースが含まれます。
単相システムは、家庭でランプ、テレビ、セントラルエアコンなどの120Vおよび240Vの電化製品に電力を供給するために使用されます。
二相 3 線式システムには 2 つの電源があり、2 番目の電源によって生成される電圧はもう 1 つより 90 度遅れます。
対照的に、三相 4 線式システムは、同じ振幅、周波数、および位相差 120 度の 3 つのソースで構成され、3 つの負荷に接続されています。
三相電源と三相負荷は、Y接続またはデルタ接続のいずれかです。
これらの回路は、誘導電動機への電力供給などの産業用アプリケーションで使用され、必要に応じて単相入力を提供するために使用できます。
これらのシステムの瞬時電力は、単相システムによって供給される脈動よりもはるかに低い脈動を持ち、より均一な電力伝送とより少ない振動を保証します。
同じ電力を伝送するために必要な導体材料やワイヤが少なくて済むため、単相よりも経済的です。

三相交流回路

Three-Phase Circuits

AC 配電システムには、単相、二相、三相システムの 3 つのカテゴリがあります。住宅環境で一般的な単相回路は、通常、単一の AC 電源をさまざまな負荷に接続する 2 線式システムを採用しています。これらの回路は、ランプ、テレビ、電子レンジなど、120 ボルト (V) および 240 V で動作する標準的な家庭用電化製品をサポートします。1895 年に設置された最初の発電機であるナイアガラパークス水力発電所は二相式で、ニコラ・テスラによって設計されました。二相供給システムはあまり一般的ではなく、三線式システムには、互いに 90 度位相がずれた 2 つの電圧源が組み込まれています。

三相 4 線式システムは、産業用途で最も普及しています。このシステムは、振幅と周波数は同じですが、互いに 120 度の位相差がある 3 つの AC 電源で構成されます。このようなシステムの負荷は、Y (スター) 構成またはデルタ (Δ) 構成のいずれかで接続できます。

三相回路の利点は、効率と安定性にあります。単相システムよりも脈動が少なく電力を供給できるため、電力伝送がスムーズになり、振動が最小限に抑えられます。これは、誘導モーターなどの産業機械にとって重要な要素です。もう 1 つの利点は、一定量の電力を伝送するために必要な導体材料の量が少なくなることです。これにより、三相システムは単相システムよりもコスト効率が高くなります。

Y 接続の 三相システムにおける線間電圧と相間電流の関係は、次の式で表されます。

<img alt="Equation 1" src="/files/ftp_upload/15126/15126_Equation_1.svg" style="height: 22px;">
<img alt="Equation 2" src="/files/ftp_upload/15126/15126_Equation_2.svg" style="height: 22px;">

Δ 接続システムの場合は次の式で表されます。

<img alt="Equation 3" src="/files/ftp_upload/15126/15126_Equation_3.svg" style="height: 20px;">
<img alt="Equation 4" src="/files/ftp_upload/15126/15126_Equation_4.svg" style="height: 22px;">

これらの式は、線間電圧と相間電流の関係と各相間の電圧と相間電流の関係を示しており、3 相システムの総電力を計算する際に重要です。Y 接続と Δ 接続の両方の総電力は、次の式で求めることができます。

<img alt="Equation 5" src="/files/ftp_upload/15126/15126_Equation_5.svg" style="height: 20px;">

ϕ は力率角で、電力伝送効率に影響します。

一般に、AC配電システムは、単相、二相、または三相に分類されます。
単相回路には、単一のソースが含まれます...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

三相回路

KEY TERMS AND CONCEPTS

主要用語および概念

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 and 240 V.

Two-phase supply systems are less common. The first generators at the Niagara Falls hydro plant, installed in 1895, used two-phase power and were designed by Nikola Tesla. In a two-phase system, a three-wire setup uses two voltage sources that are 90 degrees out of phase.

Three-phase systems are used most often in industrial settings. A three-phase, four-wire system uses three AC sources with the same amplitude and frequency, and each source is shifted by 120 degrees. Loads in these systems can be connected in a Y, or star, configuration or in a delta (Δ) configuration.

Three-phase circuits are valued for efficiency and stability. They deliver power with less pulsation than single-phase systems, so the flow is smoother and vibrations are reduced. This matters for industrial machines such as induction motors. Three-phase systems also need less conductor material to deliver the same amount of power, which makes them more cost-effective than single-phase systems.

The line and phase values are related differently in Y-connected and Δ-connected systems. These relationships between line-to-line voltage and current and the values in each phase are important when calculating total power. Total power in both Y and Δ connections is found using an equation that includes the power factor angle, φ, which affects power transmission efficiency.

How Three-Phase Power Delivers Electricity

how-three-phase-power-delivers-electricity

three-phase circuits

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

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...

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

Explore how three-phase AC power works, why industry uses Y and delta connections, and how smoother, more efficient power delivery is calculated.

How Three-Phase Power Delivers Electricity | 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 Three-Phase Power Delivers Electricity

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