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

三相母線でフェーズ a からアースまでの 1 つのラインとアース間の故障 (故障インピーダンスを含む) について考えてみます。このインピーダンスは、ボルトで固定された故障ではゼロで、アーク放電故障のアーク インピーダンスに等しく、伝送線路絶縁体のフラッシュオーバー時の全故障インピーダンスを表します。
位相領域の故障状態はシーケンス領域に変換され、シーケンス電流と相電流が導出されます。
ライン間障害は、フェーズ b と c の間で発生します。前回と同様に、位相領域条件はシーケンス領域に変換され、位相電流とシーケンス電流の関係が確立されます。
これらの故障状態は、正と負のシーケンス ネットワークを故障インピーダンスを介して故障端子で並列に接続することで満たされます。
最後に、フェーズbからフェーズcまで、故障インピーダンスを介してグランドへの二重線路故障が発生します。
次に、位相領域の故障状態が決定され、ゼロ、正、および負のシーケンスネットワークを故障端子で並列に接続することで満たされるシーケンスドメインに変換されます。
このプロセスにより、シーケンスの故障電流とライン-グランド間電圧が決定されます。

障害の種類

Fault Types

3 相バスの A 相から接地までの単一の線路接地故障を解析する場合、故障インピーダンスを考慮することが重要です。このインピーダンスは、ボルト故障の場合はゼロ、アーク故障の場合はアーク インピーダンスに等しく、送電線絶縁体のフラッシュオーバーの場合は合計故障インピーダンスを表します。シーケンス電流と位相電流を導出するには、故障状態を位相領域からシーケンス領域に変換します。 
相 B と相 C の間で発生する線間故障の場合、相領域の状態は同様にシーケンス領域に変換されます。この変換により、相電流とシーケンス電流の関係が確立されます。これらの故障状態では、正相ネットワークと逆相ネットワークが故障インピーダンスを介して故障端子で並列に接続され、故障の正確な表現が保証されます。 
二重線対地故障の場合、これは B 相から C 相にかけて故障インピーダンスを介して接地されるため、まず故障状態を位相領域で判定する必要があります。次に、これらの状態をシーケンス領域に変換します。このプロセスでは、ゼロ シーケンス、正シーケンス、および負シーケンスのネットワークを故障端末で並列に接続します。これにより、シーケンス故障電流と線対地電圧を正確に判定できます。 
この障害解析アプローチでは、位相領域とシーケンス領域の間で状態を変換することで、障害電流と障害電圧の包括的な評価が可能になります。これにより、関連するすべてのネットワーク接続と障害インピーダンスが適切に考慮され、障害がシステムに与える影響を詳細に把握できるようになります。

三相母線でフェーズ a からアースまでの 1 つのラインとアース間の故障 (故障インピーダンスを含む) について考えてみます。このインピーダンスは、ボルトで固定された...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

Symmetrical and Unsymmetrical Faults

対称故障および非対称故障

KEY TERMS AND CONCEPTS

主要用語と概念

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 電気工学 は、電気回路の基本概念と回路解析テクニックを網羅したアニメーションビデオシリーズです。オペアンプと回路変換および 1 次・ 2 次回路の概念を網羅しています。実験を撮影した実写動画では、設計例や現代社会での応用が含まれており、複雑な概念も分かりやすく学習いただけます。

electrical engineering

Power System Faults in Sequence Networks

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