Name: transformer sequence networks in per unit
Uploaded: 2024-11-21T14:54:31.000Z
Duration: 1 min 26 s
Channel: JoVE

Um transformador YY ideal aterrado por impedâncias neutras tem redes de sequência por unidade semelhantes a um transformador monofásico quando correntes de sequência positiva ou negativa balanceadas fluem, negando correntes neutras e quedas de tensão.
As correntes de sequência zero de todas as três fases se combinam para formar uma corrente neutra, causando quedas de tensão na impedância neutra e influenciando a tensão do enrolamento de baixa tensão.
Os transformadores YY práticos incluem impedâncias externas em suas redes de sequência por unidade. Cada fase representa um resistor de perda de núcleo em paralelo com uma indutância de magnetização.
Esses transformadores têm impedâncias idênticas de sequência positiva e negativa por unidade, enquanto a rede de sequência zero depende de impedâncias neutras.
Os transformadores delta-delta têm redes de sequência positiva e negativa idênticas, com impedâncias por unidade independentes das conexões de enrolamento.
Para modelar a sequência por unidade para trifásicos, transformadores de três enrolamentos são criados conectando três transformadores monofásicos comparáveis usando uma base S comum e bases de tensão proporcionais.
Na rede de sequência zero, a conexão de alta tensão depende da configuração dos enrolamentos de alta tensão.

modelos de sequência por unidade

Per-Unit Sequence Models

Um transformador Y-Y ideal, aterrado por impedâncias neutras, exibe redes de sequência por unidade semelhantes às de um transformador ideal monofásico quando submetido a correntes de sequência positiva ou negativa balanceadas. Essas correntes não produzem correntes neutras e suas quedas de tensão associadas.


 Correntes de sequência zero, que são idênticas em magnitude e fase, geram uma corrente neutra, resultando em quedas de tensão na impedância neutra e no enrolamento de baixa tensão. Se o neutro do transformador não estiver aterrado, as correntes de sequência zero não podem fluir para o solo, mas ainda podem circular dentro dos enrolamentos.


 As redes de sequência por unidade dos transformadores Y-Y práticos incorporam impedâncias externas. Seus ramos de derivação representam uma carga de impedância Y balanceada, com cada fase correspondendo a um resistor de perda de núcleo paralelo à indutância de magnetização. Esses transformadores possuem impedâncias de sequência positiva e negativa por unidade idênticas, enquanto as impedâncias neutras influenciam a rede de sequência zero.


 Os transformadores delta-delta apresentam redes de sequência por unidade com impedâncias de sequência positiva e negativa idênticas. No entanto, diferentes conexões de enrolamento podem influenciar essas impedâncias em transformadores práticos. Modelos de sequência por unidade de transformadores trifásicos e de três enrolamentos podem ser construídos conectando três transformadores monofásicos idênticos, usando uma base S comum para terminais e bases de tensão proporcionais.


 Na rede de sequência zero geral, a configuração dos enrolamentos de alta tensão determina a conexão de alta tensão. As impedâncias da rede de sequência negativa por unidade sempre correspondem às impedâncias da rede de sequência positiva.

Modelos de Sequência por Unidade

Um transformador YY ideal aterrado por meio de impedâncias neutras tem redes de sequência por unidade semelhantes a um transformador monofásico quando balanceado positivo ou ...

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Electrical Engineering

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Unit 1

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Symmetrical and Unsymmetrical Faults

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transformer sequence networks in per unit

Transformer sequence networks in per unit show how three-phase transformers respond to positive-, negative-, and zero-sequence currents. For an ideal Y-Y transformer grounded through neutral impedances, the per-unit sequence networks act much like those of a single-phase ideal transformer when the current is balanced. Balanced positive-sequence and negative-sequence currents do not create neutral current, so they do not cause voltage drops across the neutral path.

Zero-sequence current behaves differently because all three phase currents have the same magnitude and phase. This creates a neutral current and produces voltage drops across both the neutral impedance and the low-voltage winding. If the neutral is not grounded, zero-sequence current cannot flow to ground, but it can still circulate inside the windings.

Practical Y-Y transformers add external impedances to the per-unit sequence network. Their shunt branches represent a balanced-Y impedance load, with each phase modeled by a core loss resistor in parallel with the magnetizing inductance. In these transformers, the per-unit positive-sequence and negative-sequence impedances are the same, while the neutral impedances affect the zero-sequence network.

Delta-delta transformers also have identical per-unit positive-sequence and negative-sequence impedances. In practical transformers, however, the winding connection can change these impedances. Three-phase, three-winding transformer models can be built by connecting three identical single-phase transformers with a common S-base for the terminals and proportional voltage bases. In the general zero-sequence network, the high-voltage winding configuration sets the high-voltage connection, and the negative-sequence network impedance always matches the positive-sequence network impedance.

Transformer Sequence Networks in Per Unit

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per-unit sequence models

Transformer sequence networks in per unit show how three-phase transformers respond to positive-, negative-, and zero-sequence currents. For an ideal Y-Y transformer grounded through neutral impedances, the per-unit sequence networks act much like those of a single-phase ideal transformer when the current is balanced. Balanced positive-sequence and negative-sequence currents do not create neutral current, so they do not cause voltage drops across the neutral path. Zero-sequence current behaves...

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key terms and concepts

Learn how Y-Y, delta-delta, and three-winding transformers use per-unit sequence networks to model positive, negative, and zero-sequence currents.

Transformer Sequence Networks in Per Unit | 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

Transformer Sequence Networks in Per Unit

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