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

Un transformador Y-Y ideal conectado a tierra a través de impedancias neutras tiene redes de secuencia por unidad similares a un transformador monofásico cuando fluyen corrientes equilibradas de secuencia positiva o negativa, negando las corrientes neutras y las caídas de voltaje.
Las corrientes de secuencia cero de las tres fases se combinan para formar una corriente neutra, lo que provoca caídas de voltaje a través de la impedancia neutra e influye en el voltaje del devanado de bajo voltaje.
Los transformadores Y-Y prácticos incluyen impedancias externas en sus redes de secuencia por unidad. Cada fase representa una resistencia de pérdida de núcleo en paralelo con una inductancia de magnetización.
Estos transformadores tienen impedancias de secuencia positiva y negativa idénticas por unidad, mientras que la red de secuencia cero depende de impedancias neutras.
Los transformadores delta-delta tienen redes de secuencia positiva y negativa idénticas, con impedancias por unidad independientes de las conexiones de los devanados.
Para modelar la secuencia por unidad para trifásicos, los transformadores de tres devanados se crean conectando tres transformadores monofásicos comparables utilizando una base S común y bases de voltaje proporcional.
En la red de secuencia cero, la conexión de alta tensión depende de la configuración de los devanados de alta tensión.

modelos de secuencia por unidad

Per-Unit Sequence Models

Un transformador Y-Y ideal, conectado a tierra a través de impedancias neutras, muestra redes de secuencia por unidad similares a las de un transformador ideal monofásico cuando se lo somete a corrientes equilibradas de secuencia positiva o negativa. Estas corrientes no producen corrientes neutras ni sus caídas de tensión asociadas.
Las corrientes de secuencia cero, que son idénticas en magnitud y fase, generan una corriente neutra, lo que produce caídas de tensión en la impedancia neutra y en el devanado de baja tensión. Si el neutro del transformador no está conectado a tierra, las corrientes de secuencia cero no pueden fluir hacia tierra, pero sí pueden circular dentro de los devanados.
Las redes de secuencia por unidad de los transformadores Y-Y prácticos incorporan impedancias externas. Sus derivaciones representan una carga de impedancia Y equilibrada, en la que cada fase corresponde a una resistencia de pérdida de núcleo paralela a la inductancia magnetizante. Estos transformadores poseen impedancias de secuencia positiva y negativa por unidad idénticas, mientras que las impedancias neutras influyen en la red de secuencia cero.
Los transformadores delta-delta presentan redes de secuencia por unidad con impedancias de secuencia positiva y negativa idénticas. Sin embargo, las diferentes conexiones de los devanados pueden influir en estas impedancias en los transformadores prácticos. Los modelos de secuencia por unidad de transformadores trifásicos de tres devanados se pueden construir conectando tres transformadores monofásicos idénticos, utilizando una base S común para terminales y bases de tensión proporcionales.
En la red de secuencia cero general, la configuración de los devanados de altas tensión determina la conexión de alta tensión. Las impedancias de la red de secuencia negativa por unidad siempre coinciden con las impedancias de la red de secuencia positiva.

Modelos de secuencia por unidad

Un transformador Y-Y ideal conectado a tierra a través de impedancias neutras tiene redes de secuencia por unidad similares a un transformador monofásico cuando está equilibrado, positivo o ...

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JoVE Core

Electrical Engineering

Ingeniería Eléctrica

Unit 1

Unidad 1

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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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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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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