Name: generator sequence currents and impedances
Uploaded: 2024-11-21T14:54:31.000Z
Duration: 1 min 24 s
Channel: JoVE

中性インピーダンスを介して接地されたY接続同期発電機は、正のシーケンス部品のみでバランスの取れた内部位相電圧を生成するように設計されています。
ジェネレータのシーケンスネットワークには、正のシーケンスネットワークにのみソース電圧が含まれ、端子のライン-グランド間電圧のシーケンス成分が示されています。
中性線インピーダンスの電圧降下は、ゼロシーケンス電流、つまり発電機のゼロシーケンスインピーダンスと直列の中性線インピーダンスによってのみ発生します。
発電所では、同期発電機の固定子は、定常状態の条件下でバランスの取れた三相正のシーケンス電流を生成し、回転子と整列した正味の起磁力(MMF)を生成します。
平衡型の三相負シーケンス電流では、正味のMMFがロータに対抗するため、正のシーケンスインピーダンスよりも負のシーケンスインピーダンスが低くなります。
大きさと位相が同一のゼロ・シーケンス電流は、ほぼゼロの正味MMFを生成し、ゼロ・シーケンス・インピーダンスを最小にします。
シーケンスインピーダンスは回転機械によって異なり、同期、過渡、またはサブトランジェントに分類されます。
これらのネットワークは、三相同期モーターと誘導モーターの動作を簡素化します。

回転機械のシーケンスネットワーク

Sequence Networks of Rotating Machines

中性インピーダンスを介して接地された Y 接続同期発電機は、正相成分のみを含むバランスの取れた内部位相電圧を生成するように設計されています。発電機のシーケンスネットワークには、正相ネットワークのみにあるソース電圧が含まれます。発電機端子の線対接地電圧のシーケンス成分は、この構成を示しています。

ゼロシーケンス電流は、発電機の中性インピーダンスと回路内の他のゼロシーケンスインピーダンスに電圧降下を引き起こします。このため、発電機のゼロシーケンスインピーダンスと直列に、ゼロシーケンスネットワークに追加のインピーダンスが必要になります。

発電所では、定常状態にある同期発電機の固定子には、平衡した 3 相正相電流が流れます。これらの電流は、回転子の方向と一致する正味起磁力 (MMF) を生成します。一方、固定子内の平衡した 3 相負相電流は、回転子の回転に反対する回転 MMF を生成し、その結果、逆相インピーダンスが正相同期インピーダンスよりも小さくなります。

ゼロシーケンス電流は、大きさと位相が同じであるため、ほぼゼロの正味 MMF を生成します。その結果、発電機のゼロシーケンスインピーダンスは、シーケンスインピーダンスの中で通常最小になります。

回転機械のシーケンスインピーダンスは、同期、過渡、またはサブ過渡インピーダンスに分類されます。これらの分類により、シーケンスネットワークを使用して 3 相同期モーターと誘導モーターの解析を簡素化できます。

中性インピーダンスを介して接地されたY接続同期発電機は、正のシーケンスのみでバランスの取れた内部位相電圧を生成するように設計されています...

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

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 creates a voltage drop across the generator’s neutral impedance. It also drops voltage across other zero-sequence impedances in the circuit. For that reason, the zero-sequence network needs an added impedance in series with the generator’s own zero-sequence impedance.

In steady-state operation, the stator of a synchronous generator carries balanced three-phase, positive-sequence currents. These currents create a net magnetomotive force, or MMF, that moves in the same direction as the rotor. Balanced three-phase, negative-sequence currents create a rotating MMF that opposes rotor rotation. Because of this, the negative-sequence impedance is usually smaller than the positive-sequence synchronous impedance.

Zero-sequence currents have the same magnitude and phase. They produce almost no net MMF. As a result, the generator’s zero-sequence impedance is usually the smallest of the sequence impedances. In rotating machines, sequence impedances are grouped as synchronous, transient, or subtransient. These categories help simplify the analysis of three-phase synchronous and induction motors with sequence networks.

Generator Sequence Currents and Impedances

generator-sequence-currents-and-impedances

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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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Synchronous Machine Fault Current Decay

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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...

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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 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...

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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...

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Power System Faults in Sequence Networks

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key terms and concepts

Learn how positive-, negative-, and zero-sequence currents shape generator sequence networks, neutral impedance, and MMF in rotating machines.

Generator Sequence Currents and Impedances | 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

Generator Sequence Currents and Impedances

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