Name: impedance relays for fault detection
Uploaded: 2024-11-21T14:54:35.000Z
Duration: 1 min 27 s
Channel: JoVE

複雑なラジアルシステムでの時間遅延過電流リレーの調整は、マルチソース伝送ループの指向性過電流リレーと同様に困難な場合があります。
インピーダンスリレーは、電圧対電流比に応答することでこれらの問題を解決し、電流が増加して電圧が減少する三相障害時に感度が高くなります。
これらのリレーには、インピーダンスによって定義されるブロック領域とトリップ領域があります。
通常の動作では、負荷電流が少ないとインピーダンスがリレーの円の外側に保たれ、トリップが防止されますが、リレーの設定がラインインピーダンスを超える原因となる障害が発生すると、トリップが発生します。
インピーダンスリレーは無指向性ですが、指向性制約または修正インピーダンスリレーによる指向性機能を含めることができます。
インピーダンスリレーの到達距離は、その障害検出範囲を示します。通常、フェーズごとに 3 つのリレーが使用され、それぞれがリーチが長くなり、遅延が長くなります。
地絡インピーダンスリレーは、ライン-ニュートラル電圧とライン電流で動作し、三相、シングル、およびダブルのライン-グランド障害に効果的に対応します。ただし、行間の障害には鈍感です。
これらの障害では、ライン間電圧とライン電流差を使用するフェーズリレーが使用されますが、単一のライン間障害に対する感度は低くなります。

インピーダンスリレーによるライン保護

Line Protection with Impedance Relays

複雑な放射状システムにおける時間遅延型過電流リレーと、マルチソース伝送ループにおける方向性過電流リレーの調整は、困難な場合があります。インピーダンスリレーは、電圧と電流の比率に応答し、具体的にはラインの見かけのインピーダンスを測定することで、これらの問題に対処します。これらのリレーは、障害時に電流が増加して電圧が減少するにつれて感度が高まり、見かけのインピーダンスが減少します。 
通常の状態では、低負荷電流により測定インピーダンスがリレーのトリップ領域外に保たれ、不要なトリップが防止されます。障害が発生すると、インピーダンスがリレーのトリップ領域に低下し、トリップが発生します。通常は方向性がありませんが、インピーダンスリレーには、方向性制限または修正されたインピーダンスリレーを介して方向性機能を備えることができます 。
インピーダンスリレーの到達範囲は、その障害検出範囲を示します。通常、1 つのインピーダンスリレーを複数の領域で動作するように設定できます。各領域の到達範囲は徐々に拡大し、遅延も長くなります。地絡障害インピーダンスリレーは、線対中性電圧と線電流を使用して動作し、線対接地障害と線対接地障害に効果的に対応しますが、線対線障害には反応しません。 
線間故障の場合、線間電圧と線間電流の差を利用する位相リレーが使用されます。これらのリレーは線間故障には効果的ですが、単一線対地故障に対する感度は低くなります。リレー感度のこの差別化により、適切なリレーが特定の故障タイプに応答し、電力システム全体の保護と信頼性が向上します。 
最新のデジタルインピーダンスリレーは、自己監視、通信機能、正確なタイミング調整などの高度な機能を備えており、電力システム保護の信頼性と有効性がさらに向上します。これらのリレーの設定を慎重に調整することで、電力システムは高いレベルの障害検出と分離を実現し、安定性を維持し、中断を最小限に抑えることができます。

複雑なラジアルシステムでの時間遅延過電流リレーの調整は、マルチソースの指向性過電流リレーと同様に困難な場合があります...

Education

JoVE Core

Electrical Engineering

電気工学

Unit 1

ユニット1

System Protection

システム保護

KEY TERMS AND CONCEPTS

主要用語と概念

impedance relays for fault detection

Impedance relays help protect power lines by watching the voltage-to-current ratio on a line. They measure the apparent impedance, which is the electrical opposition the relay sees at that point in the system. This makes them useful when time-delay overcurrent relays are hard to coordinate in complex radial systems and when directional overcurrent relays are difficult to use in multi-source transmission loops.

These relays respond strongly during a fault. As current rises and voltage falls, the apparent impedance drops. Under normal load, the current is low, so the measured impedance stays outside the relay’s tripping region and the line does not trip by mistake. When a fault drives the impedance into that tripping region, the relay operates.

Impedance relays are usually non-directional, but they can be made directional with a directional restraint or a modified relay design. Their reach is the fault detection range, and one relay can often be set with several zones. Each zone has a longer reach and a longer time delay, which helps coordinate protection across the line.

Ground fault impedance relays use line-to-neutral voltages and line currents. They can respond to single line-to-ground and double line-to-ground faults, but they do not detect line-to-line faults well. For line-to-line faults, phase relays are used instead. These relays use line-to-line voltages and the differences in line currents, so they are effective for line-to-line faults but less sensitive to single line-to-ground faults.

This split in relay sensitivity helps the right device respond to the right fault type. Modern digital impedance relays add self-monitoring, communication features, and precise timing adjustments. With careful setting coordination, power systems can detect faults quickly, isolate damaged sections, and stay more stable with fewer interruptions.

Impedance Relays for Fault Detection

instrument transformers

Voltage and Current Sensing in Power Grids

Instrument transformers help power substations measure voltage and current safely. They create isolated replicas of electrical signals for measurement and protection. These devices support protective relays and other monitoring equipment that keep power systems stable and reliable. The two main types are voltage transformers, or VTs, and current transformers, or CTs. A voltage transformer reduces the primary voltage to a lower level that relays and measuring devices can use. A current...

overcurrent relays

Relay Settings for Circuit Fault Protection

Overcurrent relays protect circuits by sensing excess current through the secondary side of a current transformer. They are an important part of circuit protection and help keep power systems stable when a fault occurs. Two main relay types are used here: instantaneous and time-delay overcurrent relays. An instantaneous relay trips right away when current rises above the pickup current, which is the preset level that starts the relay. It then energizes the circuit breaker trip coil at once,...

radial system protection

Breaker Coordination in Radial Systems

Breaker coordination in radial systems uses time-delay overcurrent relays to limit load interruption. When a fault happens, the nearest breaker should open first. Upstream breakers stay closed because they are set with longer delays. This lets the fault be isolated while the rest of the system keeps running. If a fault is downstream of the third breaker, only the third breaker should trip. That removes power from the load beyond the fault. The second breaker keeps a longer delay setting, so...

reclosers and fuses

Fault Coordination with Reclosers and Fuses

Fault coordination with reclosers and fuses helps protect radial distribution circuits. A recloser is an automatic switch that interrupts AC power and then closes again on a preset schedule. This brief outage can clear temporary faults on overhead lines, such as those caused by tree limbs or wildlife, and it can improve overall reliability. Reclosers and their ground-level hazards also matter. Contact with a recloser or with a broken energized conductor on the ground can be dangerous. That is...

directional relays

Directional Relays in Power System Protection

Directional relays help protect power systems by telling forward faults from reverse faults. They are used when fault current flows mainly in one direction on a line. This makes the relay useful for safe and efficient fault clearing. On a protected line, a fault downstream, or to the right of the current transformer, usually makes the fault current lag the bus voltage by about 90 degrees. This is called the forward direction. A fault upstream, or to the left, may make the fault current lead...

zones of protection

Power System Protection Zones

Power system protection zones divide the network into sections so faults can be isolated quickly. These zones can include generators, transformers, buses, transmission lines, distribution lines, and motors. Each zone is shown with closed dashed lines and contains one or more components. Circuit breakers are placed at the borders where protection zones meet. If a fault happens in one zone, the related breakers open and disconnect only that section. A fault in one area, such as a kitchen in the...

line protection with impedance relays

Impedance relays help protect power lines by watching the voltage-to-current ratio on a line. They measure the apparent impedance, which is the electrical opposition the relay sees at that point in the system. This makes them useful when time-delay overcurrent relays are hard to coordinate in complex radial systems and when directional overcurrent relays are difficult to use in multi-source transmission loops. These relays respond strongly during a fault. As current rises and voltage falls,...

differential relays

Differential Relay Protection in Power Systems

Differential relays protect generators, buses, and transformers by comparing currents at different points in a power system. When the currents do not match, the relay detects the difference and opens the circuit breaker. Under normal conditions, the current entering a generator, i1, equals the current leaving it, i2. If a fault occurs, these currents become unequal, and the difference current flows through the relay operating coil to trip the relay. An electromechanical differential relay is...

pilot and numeric relaying

Pilot Relays and Digital Protection

Pilot relays and numeric relays help protect power systems. Pilot relaying is a form of differential protection, which compares electrical quantities at equipment terminals through a communication channel instead of a direct relay link. It is especially useful for transmission lines with terminals far apart, often up to 80 km on 69 to 115 kV lines. Pilot relaying can use several communication channels. Pilot wires are separate electrical circuits that operate at DC, 50 to 60 Hz, or audio...

key terms and concepts

Learn how impedance relays detect power line faults by measuring apparent impedance, using zones, and matching ground or phase relays to fault type.

Impedance Relays for Fault Detection | 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

Impedance Relays for Fault Detection

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