Name: differential relay protection in power systems
Uploaded: 2024-11-21T14:54:35.000Z
Duration: 1 min 20 s
Channel: JoVE

差動リレーは、発電機、バス、変圧器を保護します。
故障のない発電機では、リレーの動作コイルに電流が流れないため、同一の変流器がリレーを非アクティブに保ちます。
フェーズとグランド間、フェーズとフェーズ間の短絡などの内部障害は、このバランスを乱し、差動電流を引き起こし、リレーをトリガーする可能性があります。
電気機械式差動リレーは、バランスビームリレーと同様に、一方の力が他方の力を上回ったときに動作します。2つの変流器は同一ではないため、同じ電流であっても、外部障害時に大きな差動電流が発生する可能性があります。
バス保護のために、各フェーズは差動リレーを使用します。1つが作動すると、バスに接続されているすべての三相回路ブレーカーが開きます。
変流器間に内部障害がない場合、差動リレー電流はゼロのままです。ただし、バス障害が発生するとゼロ以外の差動電流が発生し、リレーがトリガされます。
10MVAを超える変圧器は、保護のために差動リレーを使用します。
多巻線トランスと電圧調整トランスに特化した適応が存在します。

差動リレー

Differential Relays

差動リレーは、異なる点の電気量を比較することで、発電機、バス、変圧器を保護するために使用されます。障害が発生すると、2点間の電流の差によってリレーが作動し、回路遮断器が開きます。通常の状態では、発電機に入る電流 (i_1) と発電機から出る電流 (i_2) は等しくなります。ただし、障害が発生すると、これらの電流は等しくなくなり、差動電流がリレーの動作コイルに流れ、リレーがトリップします。バランスビームリレーと呼ばれる電気機械式差動リレーは、差動電流によって生成される電磁力の比較に基づいて動作します。動作コイルにかかる力が拘束力を超えると、リレーがトリップします。リレーの動作条件は、次の式で与えられます。

<img alt="Equation1" src="/files/ftp_upload/16167/16167_PT_Equation1.svg" style="height: 30px;">

バス保護は、差動リレーを使用してバス領域内の障害を検出することで実現されます。リレーは、バスに出入りする電流の合計がゼロでない場合、つまり障害が発生したことを示す場合に動作します。

変圧器の差動保護は、異なる巻線と巻数比が存在するため、より複雑です。変圧器が内部障害のない通常の状態で動作している場合、それぞれの変流器 (CT) 比によって調整された一次電流と二次電流はバランスがとれているはずです。しかし、内部障害の場合は、差動電流がリレー動作コイルを流れ、リレーがトリップします。

3 相変圧器の場合、変圧器の巻線によって生じる位相シフトを考慮して、CT を正しく接続する必要があります。これにより、二次電流が同相になり、リレーの誤動作を防ぐことができます。Y-Δ 変圧器の場合、Y 側の CT は Δ に接続し、Δ 側の CT は Y に接続する必要があります。

差動保護方式は、多巻線変圧器、位相角調整変圧器、特殊接続の変圧器など、さまざまな変圧器構成に適応されています。

差動リレーは、発電機、バス、変圧器を保護します。
故障のない発電機では、同一の変流器がリレーを非アクティブに保ちます...

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

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 called a balance beam relay. It works by comparing the electromagnetic forces created by the differential current. The relay trips when the force on the operating coil becomes greater than the restraining force. This same basic idea is used to protect bus zones. For bus protection, the relay operates when the total current entering and leaving the bus is not zero, which signals a fault inside the bus area.

Differential protection is more complex for transformers because they have different windings and turn ratios. Under normal operation, with no internal fault, the primary and secondary currents should balance after they are adjusted for their current transformer, or CT, ratios. If an internal fault occurs, differential current flows through the relay operating coil and causes a trip.

Three-phase transformers also require the CTs to be connected correctly to match phase shifts caused by the windings. This keeps the secondary currents in phase and helps prevent unwanted relay operation. For Y-Δ transformers, the CTs on the Y side should be connected in Δ, and the CTs on the Δ side should be connected in Y. These protection methods have also been adapted for multi-winding transformers, phase-angle regulating transformers, and transformers with special connections.

Differential Relay Protection in Power Systems

differential-relay-protection-in-power-systems

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...

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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...

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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 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...

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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 differential relays protect generators, buses, and transformers by sensing current imbalance and tripping during faults, with CT connection details.

Differential Relay Protection in Power Systems | 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

Differential Relay Protection in Power Systems

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