Name: directional relays in power system protection
Uploaded: 2024-11-21T14:54:35.000Z
Duration: 1 min 25 s
Channel: JoVE

I relè direzionali, progettati per correnti di guasto unidirezionali, migliorano la sicurezza e l'efficienza del sistema di alimentazione.
Sulle linee elettriche con un relè direzionale, i guasti a destra del trasformatore di corrente causano un ritardo della corrente di guasto rispetto alla tensione del bus di quasi 90 gradi, definita direzione di avanzamento. Al contrario, i guasti sul lato sinistro provocano una corrente di guasto che porta la tensione del bus di quasi 90 gradi, definita direzione inversa
Un relè direzionale utilizza la tensione di riferimento e gli ingressi di corrente per definire le regioni di intervento e blocco in base all'angolo tra la corrente e la tensione.
In serie con un relè di sovracorrente, il relè direzionale eccita la bobina di scatto dell'interruttore solo quando la corrente secondaria del trasformatore di corrente supera il valore di attivazione del relè di sovracorrente e si trova nella direzione di intervento in avanti.
Funzionando come un contatore, i relè direzionali elettromeccanici utilizzano bobine di tensione e corrente e un elemento a disco rotante.
I guasti in avanti creano la coppia positiva massima sul disco rotante, chiudendo i contatti del relè, mentre i guasti in direzione inversa generano la coppia negativa massima, trattenuta da arresti meccanici.
Per i sistemi a due sorgenti, i relè direzionali possono superare le sfide di coordinamento, garantendo un servizio ininterrotto ai carichi durante i guasti.

relè direzionali

Directional Relays

I relè direzionali, essenziali per la gestione delle correnti di guasto unidirezionali, migliorano la sicurezza e l'efficienza dei sistemi di alimentazione. Sulle linee elettriche dotate di relè direzionali, i guasti a valle (a destra) del trasformatore di corrente in genere causano un ritardo della corrente di guasto rispetto alla tensione della sbarra di circa 90 gradi, noto come direzione in avanti. Al contrario, i guasti a monte (lato sinistro) possono far sì che la corrente di guasto anticipi la tensione della sbarra di circa 90 gradi, definita direzione inversa. Tuttavia, lo sfasamento effettivo dipende dall'impedenza del sistema e dalle condizioni di guasto specifiche.

I relè direzionali utilizzano ingressi di tensione e corrente di riferimento per definire le loro regioni di sgancio e blocco in base all'angolo tra corrente e tensione. In genere, la tensione di riferimento viene presa dalla sbarra o dalla tensione linea-terra e la corrente viene presa dal trasformatore di corrente (TC). Quando abbinato a un relè di sovracorrente, il relè direzionale attiva la bobina di sgancio dell'interruttore solo se la corrente secondaria del TC supera il valore di attivazione del relè di sovracorrente e si allinea con la direzione di sgancio in avanti.

I relè direzionali elettromeccanici funzionano in modo simile ai misuratori di wattora. Incorporano bobine di tensione e corrente insieme a un elemento a disco rotante. I guasti in direzione anteriore producono la massima coppia positiva sul disco rotante, chiudendo i contatti del relè. Al contrario, i guasti inversi generano la massima coppia negativa, che è trattenuta da arresti meccanici.

Nei sistemi a due sorgenti, i relè direzionali servono al coordinamento, assicurando un servizio continuo ai carichi durante i guasti. Distinguendo accuratamente tra condizioni di guasto in avanti e indietro, i relè direzionali consentono un isolamento dei guasti preciso e affidabile, mantenendo così la stabilità del sistema e riducendo al minimo le interruzioni. I moderni relè direzionali digitali offrono funzionalità avanzate come automonitoraggio, capacità di comunicazione e regolazioni precise della temporizzazione, migliorando ulteriormente l'affidabilità e l'efficacia della protezione del sistema di alimentazione.

Relè direzionali

I relè direzionali, progettati per correnti di guasto unidirezionali, migliorano la sicurezza e l'efficienza del sistema di alimentazione.
Sulle linee elettriche con relè direzionale, ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

System Protection

Protezione del sistema

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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 the bus voltage by nearly 90 degrees. That is the reverse direction. The exact phase shift can change with system impedance and fault conditions.

These relays compare a reference voltage and a current input to set trip and block zones. The reference voltage is often taken from the bus or from line-to-ground voltage. The current comes from the current transformer, or CT. When a directional relay works with an overcurrent relay, the breaker trip coil operates only if the CT secondary current passes the pickup value and points in the forward-tripping direction.

Electromechanical directional relays work much like watt-hour meters. They use voltage coils, current coils, and a rotating disc. Forward faults create maximum positive torque, which closes the relay contacts. Reverse faults create maximum negative torque, and mechanical stops restrain the disc.

Directional relays are especially important in two-source systems, where coordination can be difficult. They help keep loads in service during faults by isolating only the faulted section. By separating forward from reverse fault conditions, these relays support stable and reliable power system protection. Modern digital directional relays add self-monitoring, communication features, and precise timing adjustments.

Directional Relays in Power System Protection

directional-relays-in-power-system-protection

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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directional relays

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...

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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 directional relays distinguish forward and reverse faults, coordinate with overcurrent relays, and improve power system protection.

Directional Relays in Power System Protection | 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

Directional Relays in Power System Protection

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