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

I relè differenziali proteggono generatori, bus e trasformatori.
In un generatore privo di guasti, trasformatori di corrente identici mantengono il relè inattivo poiché la corrente non scorre attraverso la bobina di funzionamento del relè.
Un guasto interno, come un cortocircuito fase-terra o fase-fase, interrompe questo bilanciamento, causando corrente differenziale e potenzialmente attivando il relè.
I relè differenziali elettromeccanici, come i relè a trave di bilanciamento, funzionano quando la forza di un lato supera l'altro. Poiché non esistono due trasformatori di corrente identici, possono verificarsi correnti differenziali significative durante i guasti esterni, anche con correnti uguali.
Per la protezione del bus, ogni fase utilizza un relè differenziale. Se uno si attiva, tutti gli interruttori trifase collegati al bus si aprono.
Se non esiste alcun guasto interno tra i trasformatori di corrente, la corrente differenziale del relè rimane zero. Tuttavia, un guasto del bus genera una corrente differenziale diversa da zero, attivando il relè.
I trasformatori di dimensioni superiori a 10 MVA utilizzano relè differenziali per la protezione.
Esistono adattamenti specializzati per trasformatori multiavvolgimento e trasformatori di regolazione della tensione.

relè differenziali

Differential Relays

I relè differenziali vengono utilizzati per proteggere generatori, sbarre e trasformatori confrontando grandezze elettriche in punti diversi. Quando si verifica un guasto, la differenza di corrente tra i due punti attiva il relè, aprendo l'interruttore. In condizioni normali, la corrente che entra (i_1) e che esce (i_2) da un generatore sono uguali. Quando si verifica un guasto, tuttavia, queste correnti diventano disuguali e la corrente differenziale scorre nella bobina di azionamento del relè, causandone lo scatto. Un relè differenziale elettromeccanico, noto come relè a bilanciere, funziona in base al confronto delle forze elettromagnetiche generate dalla corrente differenziale. Il relè scatta quando la forza sulla bobina di azionamento supera la forza di contenimento. La condizione per il funzionamento del relè è data da:

<img alt="Equation1" src="/files/ftp_upload/16167/16167_PT_Equation1.svg" style="height: 30px;">

La protezione della sbarra di distribuzione si ottiene utilizzando relè differenziali per rilevare guasti all'interno della zona della sbarra. Il relè funziona quando la somma delle correnti in entrata e in uscita dalla sbarra non è zero, indicando un guasto.

La protezione differenziale per i trasformatori è più complessa a causa della presenza di avvolgimenti e rapporti di spire diversi. Quando il trasformatore funziona in condizioni normali e senza guasti interni, le correnti primaria e secondaria, regolate dai rispettivi rapporti del trasformatore di corrente (TC), dovrebbero bilanciarsi. Ma in caso di guasto interno, la corrente differenziale scorre attraverso la bobina di azionamento del relè, facendola scattare.

Per i trasformatori trifase, i TC devono essere collegati correttamente per tenere conto degli sfasamenti causati dagli avvolgimenti del trasformatore. Ciò garantisce che le correnti secondarie siano in fase, impedendo il funzionamento errato del relè. Per i trasformatori Y-Δ, i TC sul lato Y devono essere collegati a Δ e i TC sul lato Δ devono essere collegati a Y.

I metodi di protezione differenziale sono stati adattati a varie configurazioni di trasformatori, tra cui trasformatori multi-avvolgimento, trasformatori di regolazione dell'angolo di fase e trasformatori con connessioni speciali.

Relè differenziali

I relè differenziali proteggono generatori, bus e trasformatori.
In un generatore privo di guasti, trasformatori di corrente identici mantengono il relè inattivo ...

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JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

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System Protection

Protezione del sistema

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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Relay Settings for Circuit Fault Protection

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Breaker Coordination in Radial Systems

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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...

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Power System Protection Zones

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Impedance Relays for Fault Detection

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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 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

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