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

Si consideri un singolo guasto linea-terra dalla fase a alla terra in un bus trifase, inclusa un'impedenza di guasto. Questa impedenza è zero per un guasto imbullonato, è uguale all'impedenza dell'arco per un guasto ad arco elettrico e rappresenta l'impedenza totale del guasto durante un flashover dell'isolante della linea di trasmissione.
Le condizioni di guasto nel dominio di fase vengono tradotte nel dominio di sequenza, derivando le correnti di sequenza e di fase.
I guasti da linea a linea si verificano tra le fasi b e c. Come in precedenza, le condizioni del dominio di fase vengono convertite nel dominio di sequenza per stabilire la relazione tra le correnti di fase e di sequenza.
Queste condizioni di guasto sono soddisfatte collegando reti di sequenza positiva e negativa in parallelo ai terminali di guasto attraverso l'impedenza di guasto.
Infine, si verifica un doppio guasto linea-terra dalla fase b alla fase c tramite l'impedenza di guasto a terra.
Le condizioni di guasto nel dominio di fase vengono quindi determinate e trasformate nel dominio di sequenza, soddisfatte collegando le reti di sequenza zero, positiva e negativa in parallelo al terminale di guasto.
Questo processo determina la sequenza delle correnti di guasto e le tensioni linea-terra.

tipi di errore

Fault Types

Quando si analizza un singolo guasto linea-terra dalla fase A alla terra in un BUS trifase, è importante considerare l'impedenza di guasto. Questa impedenza è zero per un guasto bullonato, uguale all'impedenza di arco per un guasto ad arco e rappresenta l'impedenza di guasto totale per un flashover dell'isolatore della linea di trasmissione. Per derivare le correnti di sequenza e di fase, le condizioni di guasto vengono tradotte dal dominio di fase al dominio di sequenza.

Per i guasti linea-linea che si verificano tra le fasi B e C, le condizioni nel dominio di fase vengono convertite in modo simile nel dominio di sequenza. Questa conversione stabilisce la relazione tra le correnti di fase e quelle di sequenza. In queste condizioni di guasto, le reti a sequenza positiva e a sequenza negativa sono collegate in parallelo ai terminali di guasto attraverso l'impedenza di guasto, assicurando così la rappresentazione accurata del guasto.

Nel caso di un doppio guasto linea-terra, che si verifica dalla fase B alla C tramite l’impedenza di guasto a terra, le condizioni di guasto prima di tutto devono essere determinate nel dominio di fase. Successivamente queste condizioni vengono trasformate nel dominio di sequenza. Questo processo comporta il collegamento delle reti a sequenza zero, a sequenza positiva e a sequenza negativa in parallelo al terminale di guasto. In questo modo, le correnti di guasto di sequenza e le tensioni linea-terra possono essere determinate con precisione.

Questo approccio all'analisi dei guasti, che traduce le condizioni tra i domini di fase e di sequenza, consente la valutazione completa delle correnti e delle tensioni di guasto. Garantisce che tutte le connessioni di rete e le impedenze di guasto pertinenti siano opportunamente considerate, fornendo così una comprensione dettagliata dell'impatto del guasto sul sistema.

Tipi di errore

Si consideri un singolo guasto linea-terra dalla fase a alla terra in un bus trifase, inclusa un'impedenza di guasto. Questa impedenza è zero per un ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

Symmetrical and Unsymmetrical Faults

Guasti simmetrici e asimmetrici

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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...

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 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

Description

Transcript

Tags