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

Les transformateurs de mesure comprennent les transformateurs de tension et de courant.
L’enroulement primaire d’un transformateur de courant a généralement un seul tour ou une barre conductrice, autour de laquelle plusieurs tours de l’enroulement secondaire sont enroulés.
Le courant élevé circulant dans l’enroulement primaire induit un courant réduit dans l’enroulement secondaire. L’enroulement secondaire est généralement connecté en série aux appareils de mesure à impédance zéro pour permettre un flux de courant maximal. 
Les performances d'un transformateur de courant reposent sur la reproduction précise du courant primaire sans saturation provoquant une erreur. Cependant, les transformateurs de courant peuvent perdre du courant à l’impédance d’excitation du shunt.
Considérons maintenant les transformateurs de tension, constitués d’un enroulement primaire ayant un plus grand nombre d’enroulements que l’enroulement secondaire.
L’enroulement secondaire est connecté en parallèle à un dispositif de détection de tension à haute impédance, assurant un transfert de tension précis.
Pour la protection, les transformateurs de tension sont modélisés comme idéaux, produisant une représentation en phase réduite de la tension primaire. 
Cependant, les transformateurs de tension subissent de petites chutes de tension et des déphasages.

transformateurs d'instruments

Les transformateurs de mesure, comprenant les transformateurs de tension (TT) et les transformateurs de courant (TC), jouent un rôle crucial dans les sous-stations électriques en fournissant des répliques isolées du courant ou de la tension à des fins de mesure et de protection. Les transformateurs de tension réduisent la tension primaire à des niveaux adaptés au fonctionnement et à la mesure du relais, tandis que les transformateurs de courant réduisent le courant primaire. L'enroulement primaire d'un transformateur de courant se compose souvent d'un seul tour, obtenu en enfilant le conducteur primaire du système électrique à travers son noyau, bien que certaines applications puissent nécessiter plusieurs tours primaires.

À des fins de protection, les transformateurs de tension sont idéalement conçus pour produire une représentation réduite et en phase de la tension primaire. Le secondaire d'un transformateur de tension doit être connecté à un dispositif de détection de tension à haute impédance, garantissant que la totalité de la tension secondaire apparaît à travers le dispositif de détection. Inversement, le secondaire d'un transformateur de courant doit être connecté à un dispositif de détection de courant à faible impédance, permettant à la totalité du courant secondaire de circuler à travers le dispositif de détection.

Dans les applications pratiques, les transformateurs de tension peuvent subir des chutes de tension et des différences d'angle de phase entre les côtés primaire et secondaire. De même, dans les transformateurs de courant, une partie du courant peut être divisée entre le dispositif de détection à faible impédance et l'impédance d'excitation shunt du transformateur. Les performances d'un transformateur de courant dépendent en grande partie de sa capacité à reproduire avec précision le courant primaire sans erreurs significatives ni effets de saturation.

Ces transformateurs sont essentiels au fonctionnement précis des relais de protection et des appareils de mesure, garantissant ainsi le fonctionnement sûr et fiable des systèmes électriques. En réduisant les tensions et les courants élevés, les transformateurs de mesure permettent de surveiller et de contrôler les paramètres électriques dans des plages gérables, tout en maintenant la stabilité et la protection du système.

Transformateurs d'instruments

Les transformateurs de mesure comprennent les transformateurs de tension et de courant.
L’enroulement primaire d’un transformateur de courant a généralement un seul tour ou un ...

Education

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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 Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Voltage and Current Sensing in Power Grids

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