Name: synchronous machine fault current decay
Uploaded: 2024-11-21T14:54:30.000Z
Duration: 1 min 21 s
Channel: JoVE

Se realiza una prueba de cortocircuito trifásico en una máquina síncrona descargada para estudiar su impacto.
El oscilograma de la corriente de falla de CA con su compensación de CC eliminada, correspondiente a una fase de una máquina síncrona descargada, muestra una amplitud de forma de onda decreciente desde un valor inicial alto hasta un valor de estado estacionario.
Esto se atribuye al flujo magnético causado por las corrientes de inducido de cortocircuito, que cambian de trayectorias de alta reluctancia a otras más bajas, aumentando la inductancia de la armadura. Esto se puede modelar con un circuito R-L de serie variable en el tiempo.
La teoría estándar de la máquina proporciona reactancias específicas utilizadas para calcular la corriente de falla de CA instantánea que comprende el voltaje terminal de prefalla de línea RMS a neutro.
La corriente de falla subtransitoria RMS se determina en un tiempo igual a cero por la constante de tiempo subtransitoria de cortocircuito del eje directo y, a medida que avanza el tiempo, la corriente de falla de CA RMS se acerca a su valor de estado estacionario.
Cada fase tiene un desplazamiento de CC diferente, que alcanza su punto máximo cuando alfa es igual a cero.
Las reactancias de la máquina y las constantes de tiempo, proporcionadas por los fabricantes u obtenidas de las pruebas, ayudan a predecir el comportamiento del sistema de energía durante las fallas, lo que permite el control de daños y la estabilidad del sistema.

cortocircuito trifásico: máquina síncrona sin carga

Three-Phase Short Circuit&#8212;Unloaded Synchronous Machine

Realizar una prueba de cortocircuito trifásica en una máquina sincrónica sin carga ayuda a comprender su impacto en el sistema. El oscilograma de la corriente de falla de CA, con la compensación de CC eliminada, revela que la amplitud de la forma de onda disminuye desde un valor inicialmente alto hasta un nivel de estado estable para una fase de la máquina.

Este comportamiento se produce debido al flujo magnético producido por las corrientes de armadura de cortocircuito. Inicialmente, estas corrientes siguen caminos de alta reluctancia, pero finalmente cambian a caminos de menor reluctancia, aumentando así la inductancia de la armadura. Esta dinámica se puede representar mediante un circuito de resistencia-inductor en serie (R-L) variable en el tiempo.

Según la teoría de máquinas estándar, se utilizan reactancias específicas, como reactancias subtransitorias, transitorias y de estado estable, para calcular la corriente de falla de CA instantánea. Este cálculo se basa en la tensión terminal de línea a neutro RMS previo a la falla. La corriente de falla subtransitoria RMS en el momento de la falla está determinada por la reactancia subtransitoria de cortocircuito del eje directo y la constante de tiempo asociada. Con el tiempo, la corriente de falla de CA RMS se estabiliza en su valor de estado estable.

Cada fase de la máquina experimenta un desfase de CC diferente, y el desfase máximo se produce cuando el ángulo de corriente inicial es cero. Las reactancias y las constantes de tiempo de la máquina, proporcionadas por los fabricantes o derivadas de pruebas, son cruciales para predecir el comportamiento de la máquina durante las fallas. Esta información ayuda a gestionar los posibles daños y a mantener la estabilidad del sistema durante las fallas.

Comprender estas características es esencial para diseñar sistemas de energía robustos. Los datos obtenidos de estas pruebas permiten a los ingenieros predecir cómo se comportará el sistema en condiciones de falla, lo que facilita el desarrollo de estrategias para controlar los daños y garantizar la estabilidad del sistema. Este enfoque garantiza que los sistemas de energía puedan soportar fallas y continuar operando de manera confiable, manteniendo así la integridad y seguridad de las redes eléctricas.

Cortocircuito trifásico: máquina síncrona sin carga

Se realiza una prueba de cortocircuito trifásico en una máquina síncrona descargada para estudiar su impacto.
El oscilograma de la corriente de falla de CA con su ...

three-phase-short-circuitunloaded-synchronous-machine

Education

Educación

JoVE Core

Electrical Engineering

Ingeniería Eléctrica

Unit 1

Unidad 1

Symmetrical and Unsymmetrical Faults

Fallas Simétricas y Asimétricas

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

synchronous machine fault current decay

A three-phase short circuit on an unloaded synchronous machine shows how fault current changes over time. The AC fault current, with the DC offset removed, starts at a high value and then falls to a steady-state level in one phase of the machine.

This change happens because of the magnetic flux created by the short-circuit armature currents. At first, these currents flow through high-reluctance paths. They later shift to lower-reluctance paths, which increases the armature inductance. This behavior can be modeled as a time-varying series resistor-inductor, or R-L, circuit.

Standard machine theory uses sub-transient, transient, and steady-state reactances to calculate the instantaneous AC fault current. The calculation starts from the RMS line-to-neutral prefault terminal voltage. The RMS sub-transient fault current at the moment of the fault depends on the direct axis short-circuit sub-transient reactance and its time constant. As time passes, the RMS AC fault current settles to its steady-state value.

Each phase also has a different DC offset. The peak offset occurs when the initial current angle is zero. The reactances and time constants, which may come from the manufacturer or from tests, help predict machine behavior during faults. This information supports damage control and system stability, which are important for designing strong power systems and keeping electrical networks reliable and safe.

Synchronous Machine Fault Current Decay

series r&#8212;l circuit transients

Fault Current in a Series R-L Circuit

A series resistor-inductor, or R-L, circuit can model a three-phase short circuit when the switch closes at the start of the time period. In this fault condition, all three phases of an unloaded synchronous machine are short-circuited. With no fault impedance and no initial current, the starting voltage depends on the source voltage phase angle. Kirchhoff's Voltage Law, or KVL, is used to analyze the circuit and find the total asymmetrical fault current. This current has two parts. The AC...

three-phase short circuit&#8212;unloaded synchronous machine

A three-phase short circuit on an unloaded synchronous machine shows how fault current changes over time. The AC fault current, with the DC offset removed, starts at a high value and then falls to a steady-state level in one phase of the machine. This change happens because of the magnetic flux created by the short-circuit armature currents. At first, these currents flow through high-reluctance paths. They later shift to lower-reluctance paths, which increases the armature inductance. This...

power system three-phase short circuits

Subtransient Fault Current in Power Systems

Subtransient fault current analysis in a power system uses simplified models for the main equipment. Transformers are represented by their leakage reactances. Transmission lines are modeled with equivalent series reactances, and synchronous machines are treated as constant voltage sources behind their subtransient reactances. Several elements are left out of the calculation because their effect on the immediate fault current is small or they make the model harder without changing the result...

bus impedance matrix

Three-Phase Fault Current Analysis

Three-phase fault current analysis in an N-bus power system uses the positive-sequence network and the bus impedance matrix. It helps estimate subtransient fault currents when a short circuit occurs at one bus. The method uses superposition, which means the problem is split into two circuits that are studied separately. In the first circuit, all machine voltage sources are short-circuited. Only the prefault voltage source at the faulted bus remains. The positive-sequence bus impedance matrix...

circuit breaker and fuse selection

Protective Devices in Power Systems

Circuit breakers and fuses protect electrical systems from fault current and overcurrent. They help stop damage when current rises above safe limits. Both devices are chosen based on the needs of the electrical system. A circuit breaker interrupts fault current by separating its contacts. This creates an arc, which must be extinguished by elongation, cooling, or splitting, depending on the breaker design. Breakers are grouped by operating voltage and by the arc-extinguishing medium, such as...

sequence networks of rotating machines

Generator Sequence Currents and Impedances

Generator sequence currents and impedances explain how a Y-connected synchronous generator behaves under balanced and unbalanced conditions. When the generator is grounded through a neutral impedance, it is set up to produce balanced internal phase voltages with only positive-sequence components. The source voltage therefore appears only in the positive-sequence network, and the line-to-ground voltages at the generator terminals show the sequence components of this setup. Zero-sequence current...

per-unit sequence models

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...

fault types

Power System Faults in Sequence Networks

Power system faults can be analyzed by moving between the phase domain and the sequence domain. This approach helps relate fault currents and voltages for three-phase bus faults and keeps the fault impedance in the model. Fault impedance is zero for a bolted fault, equal to the arc impedance for an arcing fault, and it represents the total fault impedance for a transmission-line insulator flashover. For a single line-to-ground fault from phase A to ground, the phase-domain conditions are...

key terms and concepts

Study how a three-phase short circuit changes fault current in an unloaded synchronous machine, from sub-transient response to steady-state behavior.

Synchronous Machine Fault Current Decay | 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

Synchronous Machine Fault Current Decay

Description

Transcript

Tags