Name: three-phase fault current analysis
Uploaded: 2024-11-21T14:54:30.000Z
Duration: 1 min 24 s
Channel: JoVE

Nバス電源システムの三相故障に対するサブトランジェント故障電流の計算は、ポジティブシーケンスネットワークによってモデル化されます。母線nでの三相短絡には、重ね合わせ法による2つの回路の解析が必要です。
最初の回路では、すべてのマシン電圧源が短絡し、障害発生前の電圧源のみが障害に残ります。その節点方程式 (正のシーケンス バス アドミタンス行列を含む) を解くと、正のシーケンス バス インピーダンス行列が得られます。
最初の回路で障害のある母線に単一のソースがある場合、節点方程式の行列解によって、任意の母線の障害電流と電圧が決定されます。
2番目の回路は、障害発生前の状態を表します。プリフォールト負荷電流を無視すると、すべての電圧がプリフォールト電圧と等しくなります。短絡電流の等価回路は、自己インピーダンスと相互インピーダンスを示します。
プリフォールト負荷電流を無視すると、すべての同期マシンの内部電圧源が等しくなります。これらは、1つの同等のソースに置き換えられます。
スイッチが開いていると、すべての電流はゼロになり、各バスの電圧は等しくなります。スイッチを閉じると、母線nで短絡が発生し、電圧がゼロに低下します。

バスインピーダンス行列

Bus Impedance Matrix

N バス電力システムにおける 3 相故障の過渡故障電流を計算するには、正相ネットワークを使用します。特定のバスで 3 相短絡が発生すると、解析では重ね合わせ法を使用して 2 つの別々の回路を評価します。 
最初の回路では、すべてのマシン電圧源が短絡され、故障箇所には故障前の電圧源のみが残ります。正相バスインピーダンス行列は、正相バスアドミタンス 行列を組み込んだノード方程式を解くことで決定できます。故障したバスに単一の電圧源がある場合、ノード方程式の行列解は、任意のバスの故障電流と電圧を提供します。 
2 番目の回路は故障前の状態を反映しています。故障前の負荷電流を無視すると、すべての電圧は故障前の電圧に等しいと想定されます。短絡電流の等価回路には、自己インピーダンスと相互インピーダンスの両方が含まれます。故障前の負荷電流を無視すると、すべての同期機は等しい内部電圧源を持つと想定され、単一の等価源で表すことができます。 
最初、スイッチが開いていると、すべての電流はゼロで、各バスの電圧は等しくなります。スイッチが閉じると、指定されたバスで短絡が発生し、その電圧がゼロに低下します。 
このアプローチは、過渡故障電流とそれが電力システムに与える影響を判断するための包括的な方法を提供します。正相ネットワークに焦点を当て、重ね合わせの原理を利用することで、エンジニアは故障時のシステムの動作を正確に予測できます。この方法により、潜在的な混乱や損傷を最小限に抑えることができ、電力システムの安定性と信頼性が向上します。 
過渡故障電流のダイナミクスを理解することは、効果的な電力システムの設計と管理に不可欠です。故障状態を正確にモデル化して分析することで、エンジニアは故障の影響を軽減する戦略を立て、電気ネットワークの継続的かつ安定した運用を確保できます。この分析は、故障に耐え、故障から効率的に回復できる堅牢なシステムを設計するための基礎となります。

Nバス電源システムの三相故障に対するサブトランジェント故障電流の計算は、ポジティブシーケンスネットワークによってモデル化されます。三相...

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

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 comes from solving the nodal equations with the positive-sequence bus admittance matrix. With one voltage source at the faulted bus, the nodal solution gives the fault current and the voltage at any bus.

The second circuit represents the prefault condition. Prefault load currents are neglected, so all bus voltages are taken as equal to the prefault voltage. The short-circuit equivalent includes self-impedances and mutual impedances. With the same simplification, the synchronous machines can be replaced by one equivalent source because their internal voltage sources are assumed equal.

Before the switch closes, current is zero and each bus has the same voltage. When the switch closes, a short circuit occurs at the chosen bus and its voltage drops to zero. This approach gives a clear way to find subtransient fault currents and see how they affect the power system. Engineers use the positive-sequence network and superposition to predict fault behavior and reduce damage. The method supports power system design and management by helping improve stability, reliability, and recovery after faults.

Three-Phase Fault Current Analysis

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 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

Study how the positive-sequence network and bus impedance matrix are used to calculate subtransient three-phase fault currents in an N-bus power system.

Three-Phase Fault Current Analysis | 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

Three-Phase Fault Current Analysis

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