Name: power system faults in sequence networks
Uploaded: 2024-11-21T14:54:31.000Z
Duration: 1 min 18 s
Channel: JoVE

Considere uma única falta linha-terra da fase a para o terra em um barramento trifásico, incluindo uma impedância de falta. Essa impedância é zero para uma falta aparafusada, é igual à impedância do arco para uma falta de arco e representa a impedância total da falta durante um flashover do isolador da linha de transmissão.
As condições de falha no domínio da fase são traduzidas para o domínio da sequência, derivando correntes de sequência e fase.
Falhas linha a linha ocorrem entre as fases b e c. Como antes, as condições do domínio de fase são convertidas no domínio da sequência para estabelecer a relação entre as correntes de fase e sequência.
Essas condições de falha são satisfeitas conectando redes de sequência positiva e negativa em paralelo nos terminais de falha por meio da impedância de falta.
Finalmente, uma falha dupla linha-terra ocorre da fase b para a fase c por meio da impedância de falta para o terra.
As condições de falha no domínio da fase são então determinadas e transformadas no domínio da sequência, satisfeitas conectando as redes de sequência zero, positiva e negativa em paralelo no terminal de falta.
Este processo determina as correntes de falta de sequência e as tensões linha-terra.

tipos de falhas

Fault Types

Ao analisar uma única falha de linha para terra da fase A para terra em um barramento trifásico, é importante considerar a impedância da falha. Essa impedância é zero para uma falha parafusada, igual à impedância do arco para uma falha de arco e representa a impedância total da falha para um flashover do isolador da linha de transmissão. Para derivar correntes de sequência e fase, as condições de falha são traduzidas do domínio de fase para o domínio de sequência.


 Para falhas de linha para linha que ocorrem entre as fases B e C, as condições no domínio de fase são convertidas de forma semelhante para o domínio de sequência. Essa conversão estabelece a relação entre as correntes de fase e sequência. Nessas condições de falha, as redes de sequência positiva e sequência negativa são conectadas em paralelo nos terminais de falha por meio da impedância de falha, garantindo a representação precisa da falha.


 No caso de uma falha dupla de linha para terra, que ocorre da fase B para a fase C por meio da impedância de falha para terra, as condições de falha devem primeiro ser determinadas no domínio de fase. Essas condições são então transformadas para o domínio de sequência. Este processo envolve conectar as redes de sequência zero, sequência positiva e sequência negativa em paralelo no terminal de falha. Ao fazer isso, as correntes de falha de sequência e tensões de linha para terra podem ser determinadas com precisão.


 Esta abordagem para análise de falhas, ao traduzir condições entre os domínios de fase e sequência, permite a avaliação abrangente de correntes e tensões de falha. Ela garante que todas as conexões de rede relevantes e impedâncias de falha sejam adequadamente consideradas, fornecendo uma compreensão detalhada do impacto da falha no sistema.

Tipos de Falhas

Considere uma única falta linha-terra da fase a para o terra em um barramento trifásico, incluindo uma impedância de falta. Esta impedância é zero para um ...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

Symmetrical and Unsymmetrical Faults

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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 translated into the sequence domain to find the sequence and phase currents. The same conversion is used for a line-to-line fault between phases B and C. In that case, the positive-sequence and negative-sequence networks are connected in parallel at the fault terminals through the fault impedance.

A double line-to-ground fault from phase B to phase C through fault impedance to ground is handled in a similar stepwise way. The fault conditions are first determined in the phase domain and then transformed into the sequence domain. The zero-sequence, positive-sequence, and negative-sequence networks are connected in parallel at the fault terminal, which allows the sequence fault currents and line-to-ground voltages to be determined accurately.

Power System Faults in Sequence Networks

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...

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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...

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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 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 single line-to-ground, line-to-line, and double line-to-ground faults are converted from phase to sequence domain to find currents and voltages.

Power System Faults in Sequence Networks | 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

Power System Faults in Sequence Networks

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