Name: how three-phase power delivers electricity
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 22 s
Channel: JoVE

In generale, i sistemi di distribuzione dell'alimentazione CA sono classificati come monofase, bifase o trifase.
I circuiti monofase prevedono un'unica sorgente collegata ai carichi tramite sistemi a due fili.
I sistemi monofase sono utilizzati nelle abitazioni per alimentare apparecchi a 120 V e 240 V come lampade, TV o condizionatori d'aria centralizzati.
Un sistema bifase a tre fili ha due sorgenti, dove la tensione generata dalla seconda è in ritardo rispetto all'altra di 90 gradi.
Al contrario, un sistema trifase a quattro fili è costituito da tre sorgenti con la stessa ampiezza, frequenza e differenza di fase di 120 gradi, collegate a tre carichi.
La sorgente trifase e il carico trifase possono essere collegati a Y o a triangolo.
Questi circuiti sono utilizzati in applicazioni industriali come l'alimentazione di un motore a induzione, quando necessario, possono essere utilizzati per fornire ingressi monofase.
La potenza istantanea in questi sistemi ha una pulsazione molto più bassa rispetto a quella erogata da un sistema monofase, garantendo una trasmissione di potenza più uniforme e minori vibrazioni.
Richiedono meno materiale conduttore o filo per trasmettere la stessa potenza, il che li rende più economici rispetto ai monofase.

circuiti trifase

I sistemi di distribuzione dell'alimentazione CA hanno tre categorie: sistemi monofase, bifase e trifase. Il circuito monofase, comune negli ambienti residenziali, utilizza tipicamente un sistema a due fili che collega una singola sorgente CA a vari carichi. Questi circuiti supportano gli elettrodomestici standard che funzionano a 120 volt (V) e 240 V, come lampade, televisori e forni a microonde. I primi generatori, l'impianto idroelettrico delle Cascate del Niagara installato nel 1895, erano bifase e progettati da Nikola Tesla. Il sistema di alimentazione bifase è meno comune e il sistema a tre fili incorpora due sorgenti di tensione sfasate tra loro di 90 gradi.

Il sistema trifase a quattro fili è prevalente nelle applicazioni industriali. Questo sistema comprende tre sorgenti CA identiche in ampiezza e frequenza ma con una differenza di fase di 120 gradi tra loro. I carichi in un tale sistema possono essere collegati in una configurazione a Y (stella) o a triangolo (Δ).

Il vantaggio dei circuiti trifase risiede nella loro efficienza e stabilità. Forniscono potenza con pulsazioni inferiori rispetto ai sistemi monofase, con conseguente trasmissione di potenza più fluida e vibrazioni ridotte al minimo, un fattore cruciale per macchinari industriali come i motori a induzione. Un altro vantaggio è la ridotta quantità di materiale conduttore necessario per trasmettere una determinata quantità di potenza, che rende i sistemi trifase più convenienti rispetto alle loro controparti monofase.

Il rapporto tra le tensioni e le correnti di linea e di fase nei sistemi trifase collegati a Y è dato da:

<img alt="Equation 1" src="/files/ftp_upload/15126/15126_Equation_1.svg" style="height: 22px;">
<img alt="Equation 2" src="/files/ftp_upload/15126/15126_Equation_2.svg" style="height: 22px;">

E per i sistemi connessi in Δ:

<img alt="Equation 3" src="/files/ftp_upload/15126/15126_Equation_3.svg" style="height: 20px;">
<img alt="Equation 4" src="/files/ftp_upload/15126/15126_Equation_4.svg" style="height: 22px;">

Queste equazioni mostrano la relazione tra le tensioni e le correnti concatenate con quelle attraverso ciascuna fase, che è essenziale quando si calcola la potenza totale nei sistemi trifase. La potenza totale per entrambe le connessioni Y e Δ può essere trovata utilizzando:

<img alt="Equation 5" src="/files/ftp_upload/15126/15126_Equation_5.svg" style="height: 20px;">

dove ϕ è l'angolo del fattore di potenza, che influenza l'efficienza della trasmissione di potenza.

Circuiti Trifase

In generale, i sistemi di distribuzione dell'alimentazione CA sono classificati come monofase, bifase o trifase.
I circuiti monofase coinvolgono un'unica sorgente ...

Education

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Electrical Engineering

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Unit 1

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Three-Phase Circuits

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 and 240 V.

Two-phase supply systems are less common. The first generators at the Niagara Falls hydro plant, installed in 1895, used two-phase power and were designed by Nikola Tesla. In a two-phase system, a three-wire setup uses two voltage sources that are 90 degrees out of phase.

Three-phase systems are used most often in industrial settings. A three-phase, four-wire system uses three AC sources with the same amplitude and frequency, and each source is shifted by 120 degrees. Loads in these systems can be connected in a Y, or star, configuration or in a delta (Δ) configuration.

Three-phase circuits are valued for efficiency and stability. They deliver power with less pulsation than single-phase systems, so the flow is smoother and vibrations are reduced. This matters for industrial machines such as induction motors. Three-phase systems also need less conductor material to deliver the same amount of power, which makes them more cost-effective than single-phase systems.

The line and phase values are related differently in Y-connected and Δ-connected systems. These relationships between line-to-line voltage and current and the values in each phase are important when calculating total power. Total power in both Y and Δ connections is found using an equation that includes the power factor angle, φ, which affects power transmission efficiency.

How Three-Phase Power Delivers Electricity

how-three-phase-power-delivers-electricity

three-phase circuits

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

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

Explore how three-phase AC power works, why industry uses Y and delta connections, and how smoother, more efficient power delivery is calculated.

How Three-Phase Power Delivers Electricity | 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

How Three-Phase Power Delivers Electricity

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