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

Les relais différentiels protègent les générateurs, les bus et les transformateurs.
Dans un générateur sans défaut, des transformateurs de courant identiques maintiennent le relais inactif car aucun courant ne circule dans la bobine de fonctionnement du relais.
Un défaut interne, comme un court-circuit phase-terre ou phase-phase, perturbe cet équilibre, provoquant un courant différentiel et déclenchant potentiellement le relais.
Les relais différentiels électromécaniques, comme les relais d'équilibrage, fonctionnent lorsque la force d'un côté dépasse l'autre. Étant donné qu’il n’y a pas deux transformateurs de courant identiques, des courants différentiels importants peuvent se produire lors de défauts externes, même avec des courants égaux.
Pour la protection du bus, chaque phase utilise un relais différentiel. Si l’un d’eux s’active, tous les disjoncteurs triphasés connectés au bus s’ouvrent.
S’il n’existe aucun défaut interne entre les transformateurs de courant, le courant du relais différentiel reste nul. Cependant, un défaut de bus génère un courant différentiel non nul, déclenchant le relais.
Les transformateurs de plus de 10 MVA utilisent des relais différentiels pour la protection.
Des adaptations spécialisées existent pour les transformateurs à enroulements multiples et les transformateurs de régulation de tension.

relais différentiels

Differential Relays

Les relais différentiels sont utilisés pour protéger les générateurs, les bus et les transformateurs en comparant les quantités électriques à différents points. Lorsqu'un défaut se produit, la différence de courant entre les deux points déclenche le fonctionnement du relais, ouvrant le disjoncteur. Dans des conditions normales, le courant entrant (i_1) et sortant (i_2) d'un générateur sont égaux. Cependant, lorsqu'un défaut se produit, ces courants deviennent inégaux et la différence de courant circule dans la bobine de fonctionnement du relais, provoquant le déclenchement du relais. Un relais différentiel électromécanique, appelé relais à balancier, fonctionne sur la base de la comparaison des forces électromagnétiques générées par le courant différentiel. Le relais se déclenche lorsque la force exercée sur la bobine de fonctionnement dépasse la force de retenue. La condition de fonctionnement du relais est donnée par :

<img alt="Equation1" src="/files/ftp_upload/16167/16167_PT_Equation1.svg" style="height: 30px;">

La protection du bus est assurée par l'utilisation de relais différentiels pour détecter les défauts dans la zone du bus. Le relais fonctionne lorsque la somme des courants entrant et sortant du bus n'est pas nulle, ce qui indique un défaut.

La protection différentielle des transformateurs est plus complexe en raison de la présence de différents enroulements et rapports de transformation. Lorsque le transformateur fonctionne dans des conditions normales sans défaut interne, les courants primaire et secondaire, ajustés par leurs rapports de transformateur de courant (CT) respectifs, doivent s'équilibrer. Mais en cas de défaut interne, le courant différentiel traverse la bobine de fonctionnement du relais, provoquant son déclenchement.

Pour les transformateurs triphasés, les CT doivent être correctement connectés pour tenir compte des déphasages causés par les enroulements du transformateur. Cela garantit que les courants secondaires sont en phase, ce qui évite un fonctionnement incorrect du relais. Pour les transformateurs Y-Δ, les CT du côté Y doivent être connectés en Δ, et les CT du côté Δ doivent être connectés en Y.

Des méthodes de protection différentielle ont été adaptées à diverses configurations de transformateurs, notamment les transformateurs à enroulements multiples, les transformateurs régulateurs d'angle de phase et les transformateurs avec connexions spéciales.

Relais différentiels

Les relais différentiels protègent les générateurs, les bus et les transformateurs.
Dans un générateur sans défaut, des transformateurs de courant identiques maintiennent le relais inactif car il n’y a pas de ...

Education

Enseignement

JoVE Core

Electrical Engineering

Génie électrique

Unit 1

Unité 1

System Protection

Protection du système

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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...

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 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 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 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

Differential Relay Protection in Power Systems

Description

Transcript

Tags