Name: voltage and current sensing in power grids
Uploaded: 2024-11-21T14:54:34.000Z
Duration: 1 min 23 s
Channel: JoVE

計器用変成器には、電圧変圧器と電流変圧器が含まれます。
変流器の一次巻線には、通常、1巻線または導電バーがあり、その周りに二次巻線の複数の巻線が巻かれています。
一次巻線を流れる大電流は、二次巻線に減少した電流を誘導します。二次巻線は、通常、最大の電流の流れを可能にするために、ゼロインピーダンス測定デバイスに直列に接続されます。 
変流器の性能は、エラーの原因となる飽和なしに一次電流を正確に再現することに依存しています。ただし、変流器はシャント励起インピーダンスのために電流を失う場合があります。
次に、二次巻線よりも多くの巻線を持つ一次巻線で構成される電圧変圧器について考えてみます。
2次巻線は、高インピーダンス電圧検出デバイスに並列に接続されており、正確な電圧伝送を保証します。
保護のために、電圧トランスは理想的にモデル化され、一次電圧のスケールダウンされた同相表現が生成されます。 
ただし、電圧トランスでは、電圧降下と位相シフトが小さくなります。

計器用変成器

計器用変圧器は、電圧変圧器 (VT) と変流器 (CT) で構成され、計測や保護の目的で電流または電圧の独立したレプリカを提供することで、変電所で重要な役割を果たします。電圧変圧器は一次電圧をリレーの動作と計測に適したレベルまで下げ、変流器は一次電流をスケールダウンします。変流器の一次巻線は、電力システムの一次導体をコアに通すことで 1 ターンで構成されていることが多いですが、アプリケーションによっては複数の一次ターンが必要になる場合もあります。 
保護の目的から、電圧変圧器は、一次電圧を縮小された同相表現を生成するように設計するのが理想的です。電圧変圧器の二次側は、高インピーダンスの電圧検知装置に接続し、二次電圧全体が検知装置全体に現れるようにします。逆に、変流器の二次側は、低インピーダンスの電流検知装置に接続し、二次電流全体が検知装置を流れるようにします。 
実際のアプリケーションでは、電圧変圧器では一次側と二次側の間で電圧降下や位相角の差が生じることがあります。同様に、変流器では、低インピーダンス検出装置と変流器の並列励起インピーダンスの間で電流の一部が分割されることがあります。変流器の性能は、大きな誤差や飽和効果なしに一次電流を正確に再現できるかどうかに大きく依存します。 
これらの変圧器は、保護リレーや測定装置の正確な動作に不可欠であり、電力システムの安全で信頼性の高い動作を保証します。計器用変圧器は、高電圧と高電流をスケールダウンすることで、管理可能な範囲内で電気パラメータを監視および制御し、システムの安定性と保護を維持します。

計器用変成器には、電圧変圧器と電流変圧器が含まれます。
変流器の一次巻線は、通常、1回転または導電...

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

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 transformer scales down the primary current in the same way.

A current transformer often uses a single-turn primary winding. In many cases, the power conductor is simply threaded through the core to act as that turn. Some applications need multiple primary turns instead.

For protection, a voltage transformer should produce a scaled-down secondary voltage that stays in phase with the primary voltage. Its secondary should connect to a high-impedance voltage-sensing device. That setup lets the full secondary voltage appear across the sensing device.

A current transformer works differently. Its secondary should connect to a low-impedance current-sensing device so the full secondary current flows through the device. In practice, some current can split between the sensing device and the transformer’s shunt excitation impedance. VTs can also show voltage drops and phase-angle differences between the primary and secondary sides.

Current transformer performance depends on how well it reproduces the primary current without large errors or saturation. By reducing very high voltages and currents to manageable levels, instrument transformers let engineers monitor electrical values and protect the power system.

Voltage and Current Sensing in Power Grids

voltage-and-current-sensing-in-power-grids

instrument transformers

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 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

Explore how voltage transformers and current transformers scale high power-grid signals for safe measurement, relay operation, and system protection.

Voltage and Current Sensing in Power Grids | 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

Voltage and Current Sensing in Power Grids

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