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

通常，交流电配电系统可分为单相、两相或三相。
单相电路通过两线系统将单个电源连接到负载。
单相系统用于家庭中为120-V和240-V的电器供电，例如电灯、电视或中央空调。
两相三线制系统具有两个电源，其中一个电源产生的电压比另一个滞后90度。
相比之下，三相四线制系统由三个幅值相同、频率相同且相位差为120度的电源组成，连接至三个负载。
三相电源和三相负载可以是Y型或三角形连接。
这些电路可用于工业应用，例如为感应电动机供电，必要时也可用于提供单相输入。
这些系统中的瞬时功率比单相系统提供的功率脉动小得多，从而确保了更均匀的功率传输和更少的振动。
它们传输相同功率所需的导体材料或导线更少，因此比单相系统更经济。

三相电路

Three-Phase Circuits

交流配电系统有三种类型：单相系统、两相系统和三相系统。单相电路常见于住宅环境，通常会采用双线系统来将单一的交流电源连接到各种负载。这些电路支持工作电压为 120 伏（V）和 240 伏的标准家用电器，例如电灯、电视机和微波炉。1895 年安装的尼亚加拉瀑布水电站是第一台两相发电机，是由尼古拉-特斯拉来进行设计的。两相供电系统不太常见，三相系统中通常会包含两个相位差为 90 度的电压源。
三相四线系统在工业应用中是最为普遍的。这种系统是由三个幅度和频率相同但彼此之间相位差为 120 度的交流电源组成的。这种系统中的负载可以连接成 Y 形（星形）配置或三角形（Δ 形）配置。
三相电路的优势在于其效率和稳定性。与单相系统相比，三相系统能够提供的电力脉动更小，从而能够实现更加平稳的电力传输并最大程度地减少振动——这对于感应电机等工业机械来说是至关重要的。另一个好处则是传输一定量的电能所需的导体材料将会更少，这会使得三相系统比单相系统更具成本效益。
在 Y 形连接的三相系统中，线电压和相电压与电流之间的关系如下：
<img alt="Equation 1" src="/files/ftp_upload/15126/15126_Equation_1.svg" style="text-align: center; height: 22px;">
<img alt="Equation 2" src="/files/ftp_upload/15126/15126_Equation_2.svg" style="text-align: center; height: 22px;">
同时对于Δ形连接系统来说：
<img alt="Equation 3" src="/files/ftp_upload/15126/15126_Equation_3.svg" style="text-align: center; height: 20px;">
<img alt="Equation 4" src="/files/ftp_upload/15126/15126_Equation_4.svg" style="text-align: center; height: 22px;">
这些公式表示了线间电压和电流与每相电压和电流之间的关系，这对于计算三相系统的总功率来说是至关重要的。可使用以下公式来计算 Y 型和 Δ 型连接的总功率：
<img alt="Equation 5" src="/files/ftp_upload/15126/15126_Equation_5.svg" style="text-align: center; height: 20px;">
其中的 ϕ 是功率因数角，这会对电力传输效率产生影响。

一般来说，交流电配电系统可分为单相、两相或三相系统。  
单相电路包含一个单一电源……

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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 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 Three-Phase Power Delivers Electricity

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