Name: single-phase vs. three-phase power loss
Uploaded: 2024-07-08T13:19:58.000Z
Duration: 1 min 17 s
Channel: JoVE

家庭に電力を供給する2線式単相システムと、重機を備えた工場に電力を供給する3線式バランス3相システムを考えてみましょう。
どちらのシステムも、同じ材料と長さのワイヤを抵抗負荷で使用し、同じライン電圧と吸収電力を備えています。
単相システムでは、電流は吸収された電力と線間電圧の比率に等しくなり、電力損失は吸収された電力の2乗を線電圧の2乗で割ったものに比例します。
三相システムの場合、電流は3本のワイヤに分割され、総電力損失は異なる方法で計算されます。
2 つのシステムの電力損失の比率では、抵抗はワイヤ半径に置き換えられます。
両方のシステムで電力損失が等しい場合、単相システムのワイヤの半径は三相システムの半径の 2 倍になります。
2つのシステムに必要な材料を比較すると、単相システムは三相システムよりも33%多くの材料を使用します。
したがって、同じ電力出力の場合、三相システムは材料の消費を大幅に最小限に抑え、配電効率を向上させます。

三相および単相回路の電力分配

電気回路内の電力分配は、住宅および産業エネルギー システムの基本的な側面です。住宅環境では単相電力が一般的ですが、重機のある産業環境では三相電力が標準です。各システムはそれぞれ異なり、利点があるため、電力分配と材料効率の基本原理を理解することが重要です。

単相電力分配:

単相回路は、家庭環境では一般的で、2 線式システムが使用されます。このシステムの電流は、負荷によって吸収される電力と線間電圧によって決まります:
<img alt="Equation 1" src="/files/ftp_upload/15134/15134_Equation_1.svg" style="height: 32px;">
抵抗による配線の電力損失は、電流の 2 乗に比例します:
<img alt="Equation 2" src="/files/ftp_upload/15134/15134_Equation_2.svg" style="height: 16px;">

ここで、R は配線の抵抗です。

三相電力分配:
産業環境で最も広く使用されているバランスの取れた三相システムです。このシステムでは、電流は 3 本のワイヤに分割され、同じ電力レベルの単相システムと比較して各ワイヤの電流が減少します。各相の電流と抵抗が同じであると仮定すると、総電力損失は各相の損失の合計になります。
ワイヤ サイズと材料消費:
両方のシステムで電力損失が同じ場合のワイヤ サイズを比較すると、電力損失を増やすことなく増加した電流を流すには、単相システムのワイヤの断面積は 三相システムの断面積よりも大きくなければなりません。具体的には、単相システムでは、三相システムの各相ワイヤの断面積の 2 倍の断面積のワイヤが必要です。つまり、単相システムでは、3 相システムと同じ電力負荷を処理するために断面積の大きいワイヤが必要になり、導電材料が約 33% 増加します。

家庭に電力を供給する2線式単相システムと、重い...

power-distribution-in-three-phase-and-single-phase-circuits

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Three-Phase Circuits

三相回路

KEY TERMS AND CONCEPTS

主要用語および概念

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 current, higher current can increase power loss in the wires.

A balanced three-phase system spreads the current across three wires. This lowers the current in each wire compared with a single-phase system delivering the same power. If the current and resistance in each phase are the same, the total power loss is the sum of the loss in each phase.

Wire size also changes between the two systems. To keep equal power loss, the single-phase system needs wires with a cross-sectional area twice that of each phase wire in the three-phase system. That means single-phase wiring uses about 33% more conducting material for the same power load.

Single-Phase vs. Three-Phase Power Loss

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

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

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

Compare single-phase and balanced three-phase power distribution, wire current, resistance loss, and why single-phase systems need more conducting material.

Single-Phase vs. Three-Phase Power Loss | JoVE K12

JoVE Core 電気工学 は、電気回路の基本概念と回路解析テクニックを網羅したアニメーションビデオシリーズです。オペアンプと回路変換および 1 次・ 2 次回路の概念を網羅しています。実験を撮影した実写動画では、設計例や現代社会での応用が含まれており、複雑な概念も分かりやすく学習いただけます。

electrical engineering

Single-Phase vs. Three-Phase Power Loss

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