Name: three-phase power connections
Uploaded: 2024-07-08T13:19:57.000Z
Duration: 1 min 30 s
Channel: JoVE

Nei sistemi trifase a quattro fili, tre sorgenti di tensione collegate a Y generano tensioni di fase bilanciate.
Esistono due sequenze di fase in base all'ordine in cui le tensioni di fase raggiungono i loro valori massimi.
La prima, abc o sequenza positiva, coinvolge fasori che ruotano in senso antiorario, con Vun Vbn principale, che porta Vcn. Questa sequenza si verifica quando il rotore ruota in senso antiorario.
La seconda, acb o sequenza negativa, ha fasori che ruotano in senso antiorario, e Van conduce Vcn, che porta Vbn. Questa sequenza corrisponde alla rotazione del rotore in senso orario.
Come le fonti di tensione, i tre carichi possono essere collegati a Y o a triangolo.
Nelle configurazioni di carico bilanciato, le impedenze di fase sono uguali in grandezza e fase.
I carichi collegati a Y possono essere trasformati in configurazione a triangolo e viceversa.
In base alle configurazioni della sorgente trifase e del carico, esistono quattro possibili collegamenti.
I carichi collegati a triangolo sono più comuni della configurazione a Y a causa della facilità di aggiungere e rimuovere carichi dalle singole fasi senza causare squilibri eccessivi.
Tuttavia, le sorgenti collegate a triangolo sono meno comuni delle sorgenti collegate a Y a causa della corrente circolante nella maglia a triangolo quando le tensioni trifase sono leggermente sbilanciate.

tensioni trifase

Un generatore trifase produce tre tensioni di uguale grandezza ma con una differenza di fase di 120 gradi. Questa ampiezza identica e tensioni separate di fase uguali sono note come tensioni bilanciate e aiutano a ridurre al minimo la perdita di potenza garantendo al contempo una fornitura costante di energia ai carichi collegati. Poiché le sorgenti di tensione in un sistema trifase possono essere configurate in una formazione a stella o a triangolo, anche i carichi collegati a questi sistemi possono essere disposti in entrambe le configurazioni. Questa flessibilità nella configurazione del carico non è solo una scelta progettuale ma un modo per esercitare il controllo sul sistema. I carichi collegati in conformazione Delta, hanno un'estremità di ciascun avvolgimento di fase collegata a un punto neutro comune. Inoltre, nei carichi a configurazione Delta, le estremità degli avvolgimenti di fase sono collegate in un anello continuo, formando un triangolo. Un sistema trifase utilizza sistemi a quattro e tre fili tramite collegamenti a stella e triangolo. Le tensioni trifase nella configurazione a stella sono:


<img alt="Equation 1" src="/files/ftp_upload/15128/15128_Equation_1.svg" style="height: 16px;">
<img alt="Equation 2" src="/files/ftp_upload/15128/15128_Equation_2.svg" style="height: 16px;">
<img alt="Equation 3" src="/files/ftp_upload/15128/15128_Equation_3.svg" style="height: 16px;">


Comprendere la sequenza logica delle tre fasi è fondamentale. Nelle sequenze positiva e a-b-c, i fasori ruotano in senso antiorario, con V_an che precede V_bn, seguito da V_cn. Questa sequenza, risultante dalla rotazione del rotore in senso antiorario, è una progressione chiara e ordinata.

Nella sequenza negativa a-c-b, i fasori ruotano in senso orario, con V_an che precede V_cn e V_bn che segue per ultimo. Ciò indica un ordine di fase invertito rispetto alla sequenza positiva, che corrisponde alla rotazione del rotore in senso orario.

Ciascuna configurazione, sia con connessione a stella che a triangolo, consente una condizione di carico bilanciata e influenza la distribuzione e la gestione di tensioni e correnti nel circuito. Durante le configurazioni di carico bilanciato, le impedenze collegate su ciascuna fase sono uguali in grandezza e fase, fornendo la potenza necessaria per gestire il sistema in modo efficace.


I carichi collegati a stella possono essere trasformati in configurazione a triangolo e viceversa. In base ai tipi di connessione della sorgente e del carico, il sistema può essere configurato in quattro modi principali: stella-stella, stella-triangolo, triangolo-stella e triangolo-triangolo.

Tensioni trifase

Nei sistemi trifase a quattro fili, tre sorgenti di tensione collegate a Y generano tensioni di fase bilanciate.
Ci sono due sequenze di fasi in base all'ordine in ...

Education

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JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Three-Phase Circuits

Circuiti Trifase

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 phase winding connects to a common neutral point. In a delta connection, the phase windings join end to end in a closed triangle.

A three-phase system may use four-wire or three-wire connections through star and delta arrangements. The phase order also matters. In the positive a-b-c sequence, the phasors rotate anticlockwise, with V an leading V bn and V cn following. This sequence matches counterclockwise rotor rotation. In the negative a-c-b sequence, the phasors rotate clockwise, with V an leading V cn and V bn last. This reversed order matches clockwise rotor rotation.

Balanced load conditions are important in both wye-connected and delta-connected systems. In a balanced load, the impedances across each phase are equal in magnitude and phase. That balance helps the circuit manage voltages and currents more effectively. Star-connected loads can also be transformed into delta form, and delta loads can be transformed into star form. Based on the source and load connections, a three-phase system can be set up as wye-wye, wye-delta, delta-wye, or delta-delta.

Three-Phase Power 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 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

Learn how three-phase power uses balanced voltages, wye and delta connections, phase sequence, and balanced loads to control voltage and current flow.

Three-Phase Power 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

Three-Phase Power Connections

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