Name: directional relays in power system protection
Uploaded: 2024-11-21T14:54:35.000Z
Duration: 1 min 25 s
Channel: JoVE

指向性リレーは、一方向の障害電流用に設計されており、電力システムの安全性と効率を向上させます。
指向性リレーを備えた電力線では、変流器の右側に障害が発生すると、障害電流がバス電圧(順方向と呼ばれる)に約90度遅れます。逆に、左側の障害では、障害電流がバス電圧をほぼ90度リードし、逆方向と呼ばれます
指向性リレーは、基準電圧と電流入力を使用して、電流と電圧の間の角度に基づいてトリップ領域とブロック領域を定義します。
過電流リレーと直列に、指向性リレーは、変流器の二次電流が過電流リレーのピックアップ値を超え、順トリップ方向にある場合にのみ、ブレーカトリップコイルに通電します。
電力量計のように動作する電気機械式指向性リレーは、電圧コイルと電流コイル、および回転ディスクエレメントを使用します。
順方向の障害は、回転ディスクに最大正のトルクを生成し、リレー接点を閉じますが、逆方向の障害は、機械的な停止によって抑制された最大負のトルクを生成します。
2ソースシステムの場合、指向性リレーは調整の課題を克服し、障害時に負荷へのサービスを中断せずに保証できます。

方向リレー

Directional Relays

方向リレーは、一方向の故障電流を管理するために不可欠であり、電力システムの安全性と効率性を高めます。方向リレーを備えた電力線では、変流器の下流 (右側) の故障により、故障電流がバス電圧より約 90 度遅れる傾向が見られます。これを順方向と呼びます。対照的に、上流 (左側) の故障では、故障電流がバス電圧より約 90 度進む傾向が見られます。これを逆方向と呼びます。ただし、実際の位相シフトは、システムインピーダンスと特定の故障状態によって異なります。 
方向リレーは、基準電圧と電流の入力を使用して、電流と電圧の角度に基づいてトリップ領域とブロック領域を定義します。通常、基準電圧はバスまたはライン対接地電圧から取得され、電流は変流器 (CT) から取得されます。過電流リレーと組み合わせると、方向リレーは、CT の二次電流が過電流リレーのピックアップ値を超え、順方向トリップ方向と一致する場合にのみ、遮断器トリップコイルを有効にします。 
電気機械式方向リレーは、電力量計と同様に機能します。回転ディスク要素とともに電圧コイルと電流コイルが組み込まれています。順方向障害が発生すると、回転ディスクに最大の正トルクが発生し、リレー接点が閉じます。逆に、逆方向障害が発生すると、最大の負トルクが発生しますが、これは機械的な停止装置によって抑制されます。 
2 つの電源システムでは、方向リレーが調整の課題に対処し、障害発生時に負荷への継続的なサービスを保証します。方向リレーは、順方向障害状態と逆方向障害状態を正確に区別することで、正確で信頼性の高い障害分離を可能にし、システムの安定性を維持し、中断を最小限に抑えます。最新のデジタル方向リレーは、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をさらに高めます。

指向性リレーは、一方向の障害電流用に設計されており、電力システムの安全性と効率を向上させます。
指向性リレーを備えた電力線では、...

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

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 the bus voltage by nearly 90 degrees. That is the reverse direction. The exact phase shift can change with system impedance and fault conditions.

These relays compare a reference voltage and a current input to set trip and block zones. The reference voltage is often taken from the bus or from line-to-ground voltage. The current comes from the current transformer, or CT. When a directional relay works with an overcurrent relay, the breaker trip coil operates only if the CT secondary current passes the pickup value and points in the forward-tripping direction.

Electromechanical directional relays work much like watt-hour meters. They use voltage coils, current coils, and a rotating disc. Forward faults create maximum positive torque, which closes the relay contacts. Reverse faults create maximum negative torque, and mechanical stops restrain the disc.

Directional relays are especially important in two-source systems, where coordination can be difficult. They help keep loads in service during faults by isolating only the faulted section. By separating forward from reverse fault conditions, these relays support stable and reliable power system protection. Modern digital directional relays add self-monitoring, communication features, and precise timing adjustments.

Directional Relays in Power System Protection

directional-relays-in-power-system-protection

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 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 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,...

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 directional relays distinguish forward and reverse faults, coordinate with overcurrent relays, and improve power system protection.

Directional Relays in Power System Protection | 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

Directional Relays in Power System Protection

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