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

Na análise de corrente de falta, os transformadores são modelados usando reatâncias de fuga, enquanto as linhas de transmissão são representadas por reatâncias em série equivalentes.
As máquinas síncronas são modeladas como fontes de tensão constante por trás de reatâncias subtransitórias.
Esta análise exclui resistências de enrolamento e série, admissões de derivação, mudanças de fase delta-Y, resistência da armadura, saturação, saliência, cargas de impedância não rotativa e pequenos motores com menos de 50 cavalos de potência.
Considere um diagrama unifilar de um gerador síncrono alimentando um motor por meio de dois transformadores e uma linha de transmissão. Um curto-circuito trifásico é analisado usando o circuito equivalente de sequência positiva.
As tensões internas pré-falta das máquinas síncronas são representadas por trás de suas reatâncias subtransitórias.
A falha ocorre quando o interruptor fecha, causando uma queda de tensão no ponto de falha.
A superposição é usada para calcular a corrente de falta resultante. Se o fasorial corresponder à tensão pré-falta, o segundo circuito representa o sistema antes da falha.
Este método prevê o comportamento do sistema durante falhas, garantindo estabilidade e reduzindo danos.

curtos-circuitos trifásicos do sistema de energia

Power System Three-Phase Short Circuits

A determinação da corrente de falha subtransitória em um sistema de energia envolve representar transformadores por suas reatâncias de fuga, linhas de transmissão por suas reatâncias equivalentes em série e máquinas síncronas como fontes de tensão constante por trás de suas reatâncias subtransitórias. Nesta análise, certos elementos são excluídos, como resistências de enrolamento, resistências em série, admitâncias de derivação, deslocamentos de fase delta-Y, resistência de armadura, saturação, saliência, cargas de impedância não rotativas e pequenos motores classificados abaixo de 50 cavalos de potência, porque seu impacto na corrente de falha subtransitória é insignificante ou complica a análise sem afetar significativamente os resultados.


 Quando ocorre um curto-circuito trifásico, a falha é modelada usando duas fontes de tensão opostas com valores fasoriais iguais. O princípio da superposição é aplicado para calcular a corrente de falha. Isso envolve o uso de duas fontes de tensão opostas com valores fasoriais iguais, o que permite que o sistema seja simplificado pela remoção do valor fasor, isolando assim o componente de corrente de falha para facilitar o cálculo.


 O procedimento para determinar a corrente de falha subtransitória envolve considerar as contribuições do gerador e do motor. Ao usar as condições iniciais do circuito e aplicar as reatâncias apropriadas, a corrente de falha subtransitória pode ser calculada com precisão. Essa abordagem garante que a análise leve em consideração os efeitos imediatos da falha no sistema de energia.


 Esse método fornece insights essenciais sobre o comportamento do sistema de energia durante falhas, permitindo que os engenheiros projetem sistemas que podem suportar tais eventos. A capacidade de prever a corrente de falha subtransitória ajuda a manter a estabilidade do sistema e a minimizar danos potenciais. Entender as contribuições de diferentes componentes durante uma falha e modelar com precisão suas reatâncias é crucial para o gerenciamento eficaz de falhas.


 Ao focar nas principais reatâncias e empregar a superposição, essa análise auxilia no projeto e no gerenciamento de sistemas de energia robustos. Isso garante confiabilidade e segurança, permitindo estratégias de mitigação eficazes durante falhas. Prever o comportamento das falhas e entender seu impacto imediato é vital para manter a integridade das redes elétricas, garantindo que os sistemas de energia possam continuar operando de forma confiável em condições de falha.

Curtos-circuitos Trifásicos do Sistema de Energia

Na análise de corrente de falta, os transformadores são modelados usando reatâncias de fuga, enquanto as linhas de transmissão são representadas por reatâncias em série equivalentes.
...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

Symmetrical and Unsymmetrical Faults

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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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