Name: balanced wye-to-wye neutral current
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 19 s
Channel: JoVE

平衡的四线制Y-Y系统由三个平衡的Y形连接正弦电压源和负载组成，中性线将电源和负载的两个中性节点连接在一起。
每相的负载阻抗等于电源阻抗、线路阻抗和负载阻抗的总和。为简化系统，忽略电源阻抗和线路阻抗。
考虑到正相序，相电压决定了三线电压
将基尔霍夫电压定律应用于每相，确定线电流具有相等的幅值和120度的相位差。
它们的总和等于零，意味着中性导线中的电流为零。
在平衡的Y型系统中，输送至三相负载的总功率是每相输送功率的三倍。
对于具有不平衡负载的不平衡Y型到Y型系统，线电流不平衡，导致中性线电流不为零。
分析平衡Y型到Y型系统的另一种方法是考虑其中一相，并分析其单相等效电路以确定线电流。然后根据相序得出另外两条线电流。

y-y 电路

The Y-to-Y Circuit

在平衡的四线制星形-星形系统中，正弦电压源和负载会通过一根中性线来进行连接，中性线连接着正弦电压源和负载的中性节点。负载阻抗会跨接在负载的每个相位上。星形连接的电源能够以四线和三线的制来进行连接。当每个相上的负载相等时，三相系统则会被认为是平衡的，这将会导致所有阶段的电流和相位角都是均匀且一致的。另一方面，在不平衡系统中，负载阻抗或源电压的变化会导致出现不相等的线路电流。
对于四线制星形-星形电路配置的分析是相对简单的。在这种设置中，三相负载的每个阻抗都会直接连接到来自三相电源中相应的相电压上。假设相序为正且处于平衡状态，那么相电压则对于分析系统来说是至关重要的。这些相电压会直接影响到每个负载阻抗上的电压。
<img alt="Equation 1" src="/files/ftp_upload/15129/15129_Equation_1.svg" style="text-align: center; height: 32px;">
<img alt="Equation 2" src="/files/ftp_upload/15129/15129_Equation_2.svg" style="text-align: center; height: 32px;">
<img alt="Equation 3" src="/files/ftp_upload/15129/15129_Equation_3.svg" style="text-align: center; height: 32px;">
连接电源中性点和负载中性点导线中的电流为：
<img alt="Equation 4" src="/files/ftp_upload/15129/15129_Equation_4.svg" style="text-align: center; height: 16px;">
当基尔霍夫电压定律应用于三相平衡电路中的每一相时，便能够确认任何闭环周围的电压总和为零。这便产生了大小相等但相移为 120 度的线电流。实际上这些电流在任何一点处的总和为零，这就解释了为什么中性线在平衡条件下是不带电流的。
在不平衡的星形-星形系统中，负载阻抗或电源电压的变化会导致出现不相等的线电流。系统中的每一相都会被视为单相电路来计算其中的线电流。然而，其余各相的电流需要进行单独分析，而不是仅根据相序来进行推断，因为其中的每一相都有可能会受到其特定电气条件下的独特影响。

Y-Y 电路

平衡的四线制Y-Y系统由三个平衡的Y形连接正弦电压源和负载组成，中性线连接两者……

Education

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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

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 load impedance or source voltages differ, the system becomes unbalanced and the line currents are no longer equal.

The four-wire wye-wye circuit is relatively easy to analyze. Each load impedance is connected directly across its own phase voltage from the three-phase source. With a positive phase sequence and balanced conditions, the phase voltages are the key to finding the voltages across each load impedance.

Kirchhoff's Voltage Law applies to each phase of a balanced three-phase circuit. The sum of the voltages around any closed loop is zero. This produces line currents with equal magnitude and 120-degree phase shifts. Their sum is zero at any point, so the neutral wire carries no current when the system is balanced.

An unbalanced wye-to-wye system must be treated differently. Changes in load impedance or source voltages create unequal line currents. Each phase is handled as a single-phase circuit to find its line current. The other phases must be analyzed on their own, since each one may be affected by its specific electrical conditions rather than by phase sequence alone.

Balanced Wye-to-Wye Neutral Current

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

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 balanced and unbalanced wye-to-wye circuits work, why the neutral wire carries no current in balanced conditions, and how line currents are analyzed.

Balanced Wye-to-Wye Neutral Current | 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

Balanced Wye-to-Wye Neutral Current

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