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

Si consideri un sistema monofase a due fili che fornisce elettricità alle case e un sistema trifase bilanciato a tre fili che alimenta una fabbrica con macchinari pesanti.
Entrambi i sistemi utilizzano fili dello stesso materiale e lunghezza con carichi resistivi e hanno la stessa tensione di linea e potenza assorbita.
Nel sistema monofase, la corrente è uguale al rapporto tra la potenza assorbita e la tensione di linea, con la perdita di potenza proporzionale al quadrato della potenza assorbita diviso per il quadrato della tensione di linea.
Per il sistema trifase, la corrente è divisa in tre fili e la perdita di potenza totale è calcolata in modo diverso.
Nel rapporto tra le perdite di potenza dei due sistemi, le resistenze sono sostituite in termini di raggi del filo.
Se la perdita di potenza è uguale in entrambi i sistemi, il raggio del filo nel sistema monofase è il doppio di quello del sistema trifase.
Confrontando il materiale richiesto per i due sistemi, il sistema monofase utilizza il 33% in più di materiale rispetto al sistema trifase.
Quindi, a parità di potenza, un sistema trifase riduce sostanzialmente al minimo il consumo di materiale, migliorando l'efficienza della distribuzione dell'energia.

distribuzione della potenza nei circuiti trifase e monofase

La distribuzione dell’energia all’interno dei circuiti elettrici è un aspetto fondamentale dei sistemi energetici residenziali e industriali. Mentre l'alimentazione monofase è comune negli ambienti residenziali, l'alimentazione trifase è lo standard per gli ambienti industriali con macchinari pesanti. Ogni sistema è diverso e presenta vantaggi ed è fondamentale comprendere i principi alla base della distribuzione dell'energia e dell'efficienza dei materiali.

Distribuzione dell'energia monofase:

I circuiti monofase sono tipici negli ambienti domestici, nei quali viene utilizzato un sistema a due fili. La corrente in questo sistema è determinata dalla potenza assorbita dal carico e dalla tensione di linea:

<img alt="Equation 1" src="/files/ftp_upload/15134/15134_Equation_1.svg" style="height: 32px;">

La perdita di potenza nei fili dovuta alla resistenza è proporzionale al quadrato della corrente:

<img alt="Equation 2" src="/files/ftp_upload/15134/15134_Equation_2.svg" style="height: 16px;">

dove R è la resistenza dei fili.

Distribuzione dell'energia trifase:

In ambito industriale, viene ampiamente utilizzato un sistema trifase bilanciato. In questo sistema la corrente viene divisa tra i tre fili, riducendo la corrente in ciascun filo rispetto ad un sistema monofase con lo stesso livello di potenza. Supponendo la stessa corrente e resistenza in ciascuna fase, la perdita di potenza totale è la somma delle perdite in ciascuna fase.

Dimensioni del filo e consumo di materiale:

Quando si confrontano le dimensioni dei cavi per la stessa perdita di potenza in entrambi i sistemi, l'area della sezione trasversale dei cavi in un sistema monofase deve essere maggiore di quella in un sistema trifase per trasportare la maggiore corrente senza aumentare la perdita di potenza. Nello specifico, il sistema monofase richiede cavi con una sezione trasversale doppia rispetto a quella di ciascun filo di fase nel sistema trifase. Ciò significa che il sistema monofase richiederebbe cavi con una sezione trasversale maggiore per gestire lo stesso carico di potenza del sistema trifase, traducendosi in un aumento di circa il 33% in più di materiale conduttore.

Distribuzione della Potenza nei Circuiti Trifase e Monofase

Si consideri un sistema monofase a due fili che fornisce elettricità alle case e un sistema trifase bilanciato a tre fili che alimenta una fabbrica con pesanti ...

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

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Three-Phase Circuits

Circuiti Trifase

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 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

Single-Phase vs. Three-Phase Power Loss

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