Name: three-phase power connections
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 30 s
Channel: JoVE

在三相四线制系统中，三个星形连接的电压源产生平衡的相电压。
根据相电压达到其最大值的顺序，存在两种相序。
第一个，abc 或正序，涉及以逆时针方向旋转的相量，其中 V一个 领先的 Vbn，这会导致 Vcn当转子逆时针旋转时，出现此序列。
第二个，acb 或负序，其相量逆时针旋转，且 V一个 导联 Vcn，这会导致 Vbn该序列对应于顺时针转子旋转。
与电压源类似，三个负载可以是星形连接（Y连接）或三角形连接（delta连接）。
在平衡负载配置中，各相阻抗的幅值和相位均相等。
Y型连接的负载可以转换为三角形连接，反之亦然。
根据三相电源和负载的配置，存在四种可能的连接方式。
由于在不引起过度不平衡的情况下，可以方便地对单个相位进行负载的增减，因此三角形连接（Delta连接）的负载比星形连接（Y型配置）更为常见。
然而，当三相电压略有不平衡时，由于三角形连接的闭合回路中会产生环流，因此三角形连接的电源比星形连接的电源更少见。

三相电压

三相发电机能够产生三个幅值相等但相位差为 120 度的电压。这种幅度相同、相位相等的电压称为平衡电压，这有助于最大限度地减少功率损耗，同时还能够确保向连接的负载稳定地输送能量。由于三相系统中的电压源可以配置为星形或三角形，因此连接到这些系统的负载同样能够以任何一种配置来进行排列。负载配置的灵活性不仅仅是一种设计选择，还是对系统进行控制的一种方式。三角形连接负载中每个相绕组的一端都会连接到一个公共的中性点。相反，在三角形连接负载中，相绕组的两端会连接成一个连续的环路，从而形成一个三角形。三相系统能够通过星形和三角形连接来使用四线系统和三线系统。星形配置中的三相电压为：
<img alt="Equation 1" src="/files/ftp_upload/15128/15128_Equation_1.svg" style="text-align: center; height: 16px;">
<img alt="Equation 2" src="/files/ftp_upload/15128/15128_Equation_2.svg" style="text-align: center; height: 16px;">
<img alt="Equation 3" src="/files/ftp_upload/15128/15128_Equation_3.svg" style="text-align: center; height: 16px;">

理解三相的逻辑顺序是其中关键。在正序列和 a-b-c 序列中，相位会发生逆时针旋转，V_an 会在 V_bn 之前，V_cn 紧随其后。因此，由转子逆时针旋转所产生的这一序列是一个清晰有序的过程。
在负序列 a-c-b 中，相位是顺时针旋转的，V_an 会领先于 V_cn，V_bn 紧随其后。这表明了与正序相比，相序发生了逆转，正序列对应于转子是顺时针旋转的。
每种配置，无论是星形连接还是三角形连接，都能够实现平衡负载，同时还会对电路的电压和电流分配与管理产生影响。在平衡负载配置中，连接在每个相位上的阻抗在幅度和相位上是相等的，从而为有效管理系统提供了动力。
星形连接的负载可以转换为三角形配置，反之亦然。根据电源和负载的连接类型，可以将系统分为四种主要的配置方式：星形-星形、星形-三角形、三角形-星形和三角形-三角形。

在三相四线制系统中，三个Y型连接的电压源产生平衡的相电压。  
根据顺序不同，存在两种相序……

Education

教育

JoVE Core

Electrical Engineering

电气工程

Unit 1

第一单元

Three-Phase Circuits

三相电路

KEY TERMS AND CONCEPTS

关键术语与概念

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 phase winding connects to a common neutral point. In a delta connection, the phase windings join end to end in a closed triangle.

A three-phase system may use four-wire or three-wire connections through star and delta arrangements. The phase order also matters. In the positive a-b-c sequence, the phasors rotate anticlockwise, with V an leading V bn and V cn following. This sequence matches counterclockwise rotor rotation. In the negative a-c-b sequence, the phasors rotate clockwise, with V an leading V cn and V bn last. This reversed order matches clockwise rotor rotation.

Balanced load conditions are important in both wye-connected and delta-connected systems. In a balanced load, the impedances across each phase are equal in magnitude and phase. That balance helps the circuit manage voltages and currents more effectively. Star-connected loads can also be transformed into delta form, and delta loads can be transformed into star form. Based on the source and load connections, a three-phase system can be set up as wye-wye, wye-delta, delta-wye, or delta-delta.

Three-Phase Power Connections

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 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

Learn how three-phase power uses balanced voltages, wye and delta connections, phase sequence, and balanced loads to control voltage and current flow.

Three-Phase Power Connections | 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

Three-Phase Power Connections

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