Name: delta-wye source and load connections
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 16 s
Channel: JoVE

一个平衡的三角形-星形系统由一个平衡的三角形连接电源为一个平衡的星形连接负载供电。
在此Δ-Y电路中，假设采用正序abc来表示相电压，这些相电压同时也作为Δ连接电源的线电压。
可以通过将基尔霍夫电压定律应用于电路中的一个回路，来推导出两条支路电流之间的关系。
由于假设为正序，这些线电流之间的相位差为120度，可利用该相位差确定其中任一电流。
其余两条线路电流通过使用正相序获得。
三角-星形电路的相电流近似等于线电流。
或者，可以用等效的Y型连接电源替代三角形连接电源。
通过考虑等效单相电路并确定三相线电流，对获得的Y-Y电路进行分析。
该电路也可以转换为三角形-三角形系统进行分析，因为三角形连接的负载通常更受青睐，便于单独调整各个负载。

三角形-y 形电路

The Delta-to-Y Circuit

在三角形-星形电路中，电源会采用三角形连接的方式，而负载则会采用星形配置。这意味着三角形连接电源的相电压等于星形连接负载的线电压。两线电流之间的连接源自三角形连接电源。平衡系统中的相位差可以利用正相序来计算出一条线路中的电流。在三角形-星形系统中，由于负载的星形配置简化了来自三角形电源中的电流，因此星形连接负载中的相电流能够直接等于来自三角形电源中的线电流。从星形配置中线电流和相电流之间的关系可以看出，星形连接负载中的相电流等于三角形连接电源中的线电流。
获得线电流的另一种方法是将三角形连接电源替换为等效的星形连接电源。星形连接电源中的线电压会比其相应的相电压高 30 度。这便意味着等效星形连接电源中的每个相电压都是通过将三角形连接电源中相应的线电压除以三的平方根并将其相位偏移-30度而得出的。因此，等效星形连接电源中的相电压相应地偏移了 120 度。
通过将三角形配置转换为星形配置，系统就可以实现更好的电压调节，并允许使用中性线。该中性线能够使系统接地，并以此来提高安全性和稳定性。
平衡的三角形-三角形配置能够用于远距离输力，在这种情况下，需要将高电压降低到工业、商业和住宅用电的可用水平。

三角形-Y 形电路

一个平衡的三角形-星形系统包含一个平衡的三角形连接电源，为一个平衡的星形连接负载供电。  
在此三角形-星形电路中，正相序abc……

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

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. That relationship makes current analysis simpler in the load section.

The line currents can also be found by replacing the delta source with an equivalent wye source. In that conversion, each phase voltage is the matching line voltage divided by the square root of three and shifted by -30 degrees. The line-to-line voltages of a wye source lead the phase voltages by 30 degrees, so the equivalent wye source keeps the phases spaced 120 degrees apart.

Changing a delta connection to a star, or wye, connection can improve voltage regulation. It also allows the use of a neutral wire. That neutral wire supports grounding, which improves safety and stability. Balanced delta systems are also used for long-distance power transmission, where high voltage must later be stepped down for industrial, commercial, and residential use.

Delta-Wye Source and Load 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

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

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 a balanced delta source powers a wye load, how line and phase currents relate, and how a delta source can be converted to an equivalent wye source.

Delta-Wye Source and Load 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

Delta-Wye Source and Load Connections

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