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

К измерительным трансформаторам относятся трансформаторы напряжения и тока.
Первичная обмотка трансформатора тока обычно имеет один виток или токопроводящий стержень, вокруг которого наматывается несколько витков вторичной обмотки.
Большой ток, протекающий через первичную обмоток, индуцирует уменьшенный ток во вторичной обмотке. Вторичная обмотка обычно последовательно подключается к измерительным устройствам с нулевым импедансом для обеспечения максимального протекания тока. 
Производительность трансформатора тока зависит от точного воспроизведения первичного тока без насыщения, вызывающего ошибки. Однако трансформаторы тока могут терять часть тока для снижения импеданса возбуждения.
Теперь рассмотрим трансформаторы напряжения, состоящие из первичной обмотки, имеющей большее количество обмоток, чем вторичная обмотка.
Вторичная обмотка подключена параллельно высокоомному устройству измерения напряжения, что обеспечивает точную передачу напряжения.
Для защиты трансформаторы напряжения моделируются как идеальные, создавая уменьшенное синфазное представление первичного напряжения. 
Однако трансформаторы напряжения испытывают небольшие перепады напряжения и фазовые сдвиги.

Измерительные трансформаторы

Измерительные трансформаторы, включающие трансформаторы напряжения (ТН) и трансформаторы тока (ТТ), играют важную роль в подстанциях, обеспечивая изолированные копии тока или напряжения для измерения и защиты. Трансформаторы напряжения снижают первичное напряжение до уровней, подходящих для работы реле и измерения, в то время как трансформаторы тока уменьшают первичный ток. Первичная обмотка трансформатора тока часто состоит из одного витка, что достигается путем пропускания первичного проводника энергосистемы через его сердечник, хотя в некоторых случаях может потребоваться несколько первичных витков.

В целях защиты трансформаторы напряжения идеально спроектированы для создания уменьшенного, синфазного представления первичного напряжения. Вторичная обмотка трансформатора напряжения должна подключаться к высокоомному устройству измерения напряжения, гарантируя, что всё вторичное напряжение появляется на чувствительном устройстве. И наоборот, вторичная обмотка трансформатора тока должна подключаться к низкоомному устройству измерения тока, позволяя всему вторичному току протекать через чувствительное устройство.

В практических применениях трансформаторы напряжения могут испытывать падения напряжения и разницу фазового угла между первичной и вторичной сторонами. Аналогично, в трансформаторах тока часть тока может быть разделена между датчиком с низким импедансом и импедансом возбуждения шунта трансформатора. Производительность трансформатора тока во многом зависит от его способности точно воспроизводить первичный ток без существенных ошибок или эффектов насыщения.

Эти трансформаторы необходимы для точной работы защитных реле и измерительных приборов, обеспечивая безопасную и надежную работу энергосистем. Уменьшая высокие напряжения и токи, измерительные трансформаторы позволяют контролировать и управлять электрическими параметрами в управляемых диапазонах, поддерживая стабильность и защиту системы.

К измерительным трансформаторам относятся трансформаторы напряжения и тока.
Первичная обмотка трансформатора тока обычно имеет один виток или проводящую обмотку ...

Education

JoVE Core

Electrical Engineering

Электротехника

Unit 1

Раздел 1

System Protection

Защита системы

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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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