Name: subtransient fault current in power systems
Uploaded: 2024-11-21T14:54:30.000Z
Duration: 1 min 21 s
Channel: JoVE

En el análisis de corriente de falla, los transformadores se modelan utilizando reactancias de fuga, mientras que las líneas de transmisión se representan mediante reactancias en serie equivalentes.
Las máquinas síncronas se modelan como fuentes de voltaje constante detrás de reactancias subtransitorias.
Este análisis excluye las resistencias de devanado y en serie, las admitancias de derivación, los cambios de fase delta-Y, la resistencia del inducido, la saturación, la prominencia, las cargas de impedancia no giratoria y los motores pequeños de menos de 50 caballos de fuerza.
Considere un diagrama unifilar de un generador síncrono que alimenta un motor a través de dos transformadores y una línea de transmisión. Un cortocircuito trifásico se analiza utilizando el circuito equivalente de secuencia positiva.
Los voltajes internos previos a la falla de las máquinas síncronas están representados detrás de sus reactancias subtransitorias.
La falla ocurre cuando el interruptor se cierra, lo que provoca una caída de voltaje en el punto de falla.
La superposición se utiliza para calcular la corriente de falla resultante. Si el fasor coincide con el voltaje previo a la falla, el segundo circuito representa el sistema antes de la falla.
Este método predice el comportamiento del sistema durante las fallas, lo que garantiza la estabilidad y reduce los daños.

cortocircuitos trifásicos en sistemas eléctricos

Power System Three-Phase Short Circuits

Para determinar la corriente de falla subtransitoria en un sistema de potencia, se deben representar los transformadores por sus reactancias de fuga, las líneas de transmisión por sus reactancias en serie equivalentes y las máquinas sincrónicas como fuentes de tensión constante detrás de sus reactancias subtransitorias. En este análisis, se excluyen ciertos elementos, como las resistencias de bobinado, las resistencias en serie, las admitancias en derivación, los cambios de fase delta-Y, la resistencia de armadura, la saturación, la saliencia, las cargas de impedancia no rotatorias y los motores pequeños de potencia nominal inferior a 50 caballos de fuerza, porque su impacto en la corriente de falla subtransitoria es insignificante o complica el análisis sin afectar significativamente los resultados.

Cuando se produce un cortocircuito trifásico, la falla se modela utilizando dos fuentes de tensión opuestas con valores fasoriales iguales. El principio de superposición se aplica para calcular la corriente de falla. Esto implica el uso de dos fuentes de tensión opuestas con valores fasoriales iguales, lo que permite simplificar el sistema eliminando el valor fasorial, aislando así el componente de corriente de falla para facilitar el cálculo.

El procedimiento para determinar la corriente de falla subtransitoria implica considerar las contribuciones tanto del generador como del motor. Al utilizar las condiciones iniciales del circuito y aplicar las reactancias adecuadas, se puede calcular con precisión la corriente de falla subtransitoria. Este enfoque garantiza que el análisis tenga en cuenta los efectos inmediatos de la falla en el sistema eléctrico.

Este método proporciona información esencial sobre el comportamiento del sistema eléctrico durante fallas, lo que permite a los ingenieros diseñar sistemas que puedan soportar tales eventos. La capacidad de predecir la corriente de falla subtransitoria ayuda a mantener la estabilidad del sistema y minimizar los posibles daños. Comprender las contribuciones de los diferentes componentes durante una falla y modelar con precisión sus reactancias es crucial para una gestión eficaz de las fallas.

Al centrarse en las reactancias clave y emplear la superposición, este análisis ayuda en el diseño y la gestión de sistemas de energía robustos. Esto garantiza la confiabilidad y la seguridad, lo que permite estrategias de mitigación efectivas durante fallas. Predecir el comportamiento de las fallas y comprender su impacto inmediato es vital para mantener la integridad de las redes eléctricas, lo que garantiza que los sistemas de energía puedan seguir funcionando de manera confiable en condiciones de falla.

Cortocircuitos trifásicos en sistemas eléctricos

En el análisis de corriente de falla, los transformadores se modelan utilizando reactancias de fuga, mientras que las líneas de transmisión se representan mediante reactancias en serie equivalentes.
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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

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 much. These include winding resistances, series resistances, shunt admittances, delta-Y phase shifts, armature resistance, saturation, saliency, non-rotating impedance loads, and small motors rated below 50 horsepower. Removing these parts keeps the fault study focused on the most important reactances.

A three-phase short circuit is modeled with two opposing voltage sources that have equal phasor values. Phasors are rotating values used to describe AC voltage and current. The superposition principle is then used to find the fault current by removing the equal phasor values and isolating the fault component.

The calculation also includes the contributions from both the generator and the motor. Using the initial circuit conditions and the correct reactances, the subtransient fault current can be found accurately. This method helps engineers understand the first effects of a fault, predict system behavior, and design power systems that can better handle short-circuit events.

Subtransient Fault Current in Power Systems

subtransient-fault-current-in-power-systems

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

three-phase-short-circuitunloaded-synchronous-machine

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...

power system three-phase short circuits

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

Learn how transformers, lines, generators, and motors are modeled to calculate subtransient fault current during a three-phase short circuit.

Subtransient Fault Current in Power Systems | 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

Subtransient Fault Current in Power Systems

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