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

Os transformadores de instrumentos incluem transformadores de tensão e corrente.
O enrolamento primário de um transformador de corrente normalmente tem uma única volta ou uma barra condutora, em torno da qual várias voltas do enrolamento secundário são enroladas.
A alta corrente que flui através do enrolamento primário induz uma corrente reduzida no enrolamento secundário. O enrolamento secundário é geralmente conectado em série aos dispositivos de medição de impedância zero para permitir o fluxo máximo de corrente. 
O desempenho de um transformador de corrente depende da replicação precisa da corrente primária sem saturação causadora de erros. No entanto, os transformadores de corrente podem perder alguma corrente para desviar a impedância de excitação.
Agora, considere os transformadores de tensão, que consistem em um enrolamento primário com um número maior de enrolamentos do que o enrolamento secundário.
O enrolamento secundário é conectado em paralelo a um dispositivo de detecção de tensão de alta impedância, garantindo uma transferência de tensão precisa.
Para proteção, os transformadores de tensão são modelados como ideais, produzindo uma representação em fase reduzida da tensão primária. 
No entanto, os transformadores de tensão sofrem pequenas quedas de tensão e mudanças de fase.

transformadores de instrumentos

Transformadores de instrumentos, incluindo transformadores de tensão (VTs) e transformadores de corrente (CTs), desempenham papéis cruciais em subestações de energia, fornecendo réplicas isoladas de corrente ou tensão para fins de medição e proteção. Transformadores de tensão reduzem a tensão primária a níveis adequados para operação e medição de relés, enquanto transformadores de corrente reduzem a corrente primária. O enrolamento primário de um transformador de corrente geralmente consiste em uma única volta, obtida ao passar o condutor primário do sistema de energia por seu núcleo, embora algumas aplicações possam exigir várias voltas primárias.


 Para fins de proteção, transformadores de tensão são idealmente projetados para produzir uma representação reduzida e em fase da tensão primária. O secundário de um transformador de tensão deve se conectar a um dispositivo de detecção de tensão de alta impedância, garantindo que toda a tensão secundária apareça no dispositivo de detecção. Por outro lado, o secundário de um transformador de corrente deve se conectar a um dispositivo de detecção de corrente de baixa impedância, permitindo que toda a corrente secundária flua através do dispositivo de detecção.


 Em aplicações práticas, transformadores de tensão podem sofrer quedas de tensão e diferenças de ângulo de fase entre os lados primário e secundário. Da mesma forma, em transformadores de corrente, alguma corrente pode ser dividida entre o dispositivo de detecção de baixa impedância e a impedância de excitação de derivação do transformador. O desempenho de um transformador de corrente depende em grande parte de sua capacidade de reproduzir com precisão a corrente primária sem erros significativos ou efeitos de saturação.


 Esses transformadores são essenciais para a operação precisa de relés de proteção e dispositivos de medição, garantindo a operação segura e confiável de sistemas de energia. Ao reduzir altas tensões e correntes, os transformadores de instrumentos permitem o monitoramento e o controle de parâmetros elétricos dentro de faixas gerenciáveis, mantendo a estabilidade e a proteção do sistema.

Transformadores de Instrumentos

Os transformadores de instrumentos incluem transformadores de tensão e corrente.
O enrolamento primário de um transformador de corrente normalmente tem uma única volta ou uma ...

Education

JoVE Core

Electrical Engineering

Engenharia Elétrica

Unit 1

Unidade 1

System Protection

Proteção do Sistema

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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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