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

Сбалансированные четырехпроводные системы Y-to-Y состоят из трех сбалансированных Y-соединенных синусоидальных источников напряжения и нагрузок с нейтральным проводом, соединяющим оба нейтралевых узла источника с нагрузкой.
Импеданс нагрузки для каждой фазы равен сумме импедансов источника, линии и нагрузки. Для упрощения системы пренебрегают импедансами источника и линии.
Учитывая положительную последовательность фаз, фазные напряжения определяют трехлинейные напряжения
Закон напряжения Кирхгофа применяется к каждой фазе, и линейные токи имеют равные величины и разность фаз в 120 градусов.
Их сумма равна нулю, что подразумевает нулевой ток в нейтральном проводе.
В сбалансированной Y-образной системе общая мощность, подаваемая на трехфазную нагрузку, в три раза превышает мощность, подаваемую в каждой фазе.
В несимметричной системе Y-to-Y с несимметричной нагрузкой сетевые токи несимметричны, что приводит к ненулевому току нейтрали.
Другой метод анализа сбалансированной системы Y-to-Y заключается в рассмотрении одной фазы и анализе ее однофазной эквивалентной цепи для определения ее линейного тока. Затем фазовая последовательность дает два других линейных тока.

Схема y-к-y(“звезда” - “звезда”)

The Y-to-Y Circuit

В сбалансированной четырехпроводной системе «звезда-звезда» схема включает в себя соединенные по схеме «звезда» источники и нагрузки синусоидального напряжения, соединенные через нейтральный провод, который соединяет нейтральные узлы источника и нагрузки. Импеданс нагрузки подключается к каждой фазе нагрузки. Источник, подключенный по схеме «звезда», может быть подключен к нагрузке, подключенной по схеме «звезда», по четырехпроводной и трехпроводной схеме. Трехфазная система считается сбалансированной, когда нагрузка на каждой фазе одинакова, что приводит к однородному протеканию тока и одинаковому фазовому углу на всех ступенях. С другой стороны, в несбалансированной системе изменения импеданса нагрузки или напряжения источника приводят к неодинаковым линейным токам.
Анализ конфигурации четырехпроводной схемы «звезда-звезда» относительно прост. В этой схеме каждое сопротивление трехфазной нагрузки подключено непосредственно к соответствующему фазному напряжению от трехфазного источника. При условии прямой последовательности фаз и сбалансированных условий фазные напряжения играют важную роль в анализе системы. Эти фазные напряжения напрямую влияют на напряжения на каждом сопротивлении нагрузки.
<img alt="Equation 1" src="/files/ftp_upload/15129/15129_Equation_1.svg" style="height: 32px;">
<img alt="Equation 2" src="/files/ftp_upload/15129/15129_Equation_2.svg" style="height: 32px;">
<img alt="Equation 3" src="/files/ftp_upload/15129/15129_Equation_3.svg" style="height: 32px;">
Ток в проводе, соединяющем нейтральный узел источника с нейтральным узлом нагрузки, равен:
<img alt="Equation 4" src="/files/ftp_upload/15129/15129_Equation_4.svg" style="height: 16px;">
Закон Кирхгофа о напряжении, примененный к каждой фазе сбалансированной трехфазной цепи, подтверждает, что сумма напряжений в любом замкнутом контуре равна нулю. Это приводит к тому, что линейные токи имеют одинаковую величину, но со сдвигом фаз между ними на 120 градусов. Сумма этих токов фактически равна нулю в любой точке, что объясняет, почему в нейтральном проводе нет тока в сбалансированных условиях.
В несбалансированной системе «звезда-звезда» изменения импеданса нагрузки или напряжения источника приводят к неодинаковым линейным токам. Каждая фаза в системе рассматривается как однофазная цепь для расчета ее линейного тока. Однако, токи остальных фаз требуют индивидуального анализа, а не выводов, основанных исключительно на последовательности фаз, поскольку на каждую фазу могут влиять уникальные электрические условия.

Схема Y-к-Y(“звезда” - “звезда”)

Сбалансированные четырехпроводные системы Y-to-Y состоят из трех сбалансированных синусоидальных источников напряжения, подключенных по оси Y, и нагрузок с нейтральным проводом, соединяющим оба ...

Education

JoVE Core

Electrical Engineering

Электротехника

Unit 1

Раздел 1

Three-Phase Circuits

Трехфазные цепи

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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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