Name: impedance relays for fault detection
Uploaded: 2024-11-21T14:54:35.000Z
Duration: 1 min 27 s
Channel: JoVE

복잡한 방사형 시스템에서 시간 지연 과전류 릴레이를 조정하는 것은 다중 소스 전송 루프에서 방향성 과전류 릴레이와 마찬가지로 어려울 수 있습니다.
임피던스 계전기는 전압 대 전류 비율에 응답하여 이러한 문제를 해결하며, 전류가 증가하고 전압이 감소할 때 3상 오류 중에 더 민감해집니다.
이러한 릴레이에는 임피던스에 의해 정의되는 블록 및 트립 영역이 있습니다.
정상 작동 시 낮은 부하 전류는 임피던스를 계전기의 원 밖으로 유지하여 트립을 방지하지만, 릴레이 설정이 라인 임피던스를 초과하는 오류로 인해 트립이 발생합니다.
임피던스 릴레이는 무방향이지만 방향 제한 또는 수정된 임피던스 릴레이를 통한 방향 기능을 포함할 수 있습니다.
임피던스 릴레이의 도달 범위는 오류 감지 범위를 나타냅니다. 일반적으로 위상당 3개의 릴레이가 사용되며, 각 릴레이는 도달 범위가 증가하고 지연이 길어집니다.
접지 오류 임피던스 릴레이는 라인-중성 전압 및 라인 전류에서 작동하여 3상, 단일 및 이중 라인-접지 오류에 효과적으로 응답합니다. 그러나 라인 간 결함에 둔감합니다.
이러한 결함의 경우 라인 간 전압 및 라인 전류 차이를 사용하는 위상 릴레이가 사용되지만 단일 라인-접지 결함에 덜 민감합니다.

임피던스 릴레이를 사용한 라인 보호

Line Protection with Impedance Relays

복잡한 방사형 시스템에서 시간 지연 과전류 릴레이를 조정하고 다중 소스 전송 루프에서 방향성 과전류 릴레이를 조정하는 것은 어려울 수 있습니다. 임피던스 릴레이는 전압 대 전류 비율에 대응하여 이러한 문제를 해결하고 특히 회선의 겉보기 임피던스를 측정합니다. 이러한 릴레이는 전류가 증가하고 전압이 감소함에 따라 고장 중에 더 민감해져 겉보기 임피던스가 감소합니다.

정상 조건에서 낮은 부하 전류는 측정된 임피던스를 릴레이의 트리핑 영역 밖에 유지하여 불필요한 트립을 방지합니다. 오류가 발생하면 임피던스가 릴레이의 트리핑 영역으로 떨어져 트립이 발생합니다. 일반적으로 비방향성이지만 임피던스 릴레이는 방향성 제한 또는 수정된 임피던스 릴레이를 통해 방향성 기능을 갖출 수 있습니다.

임피던스 릴레이의 도달 범위는 오류 감지 범위를 나타냅니다. 일반적으로 단일 임피던스 릴레이는 여러 구역에서 작동하도록 설정할 수 있으며, 각 구역은 점점 더 증가하는 도달 범위와 더 긴 지연을 갖습니다. 접지 고장 임피던스 릴레이는 라인-중성 전압과 라인 전류를 사용하여 작동하며, 단일 라인-접지 및 이중 라인-접지 고장에 효과적으로 대응하지만 라인-라인 고장에는 민감하지 않습니다.

선간 고장의 경우 선간 전압과 선 전류의 차이를 사용하는 위상 릴레이가 사용됩니다. 이러한 릴레이는 선간 고장에 효과적이지만 단일 선간 접지 고장에는 덜 민감합니다. 릴레이 감도의 이러한 차별화는 적절한 릴레이가 특정 고장 유형에 대응하여 전력 시스템의 전반적인 보호 및 안정성을 향상시킵니다.

최신 디지털 임피던스 릴레이는 자체 모니터링, 통신 기능, 정밀한 타이밍 조정과 같은 고급 기능을 제공하여 전력 시스템 보호의 신뢰성과 효과를 더욱 향상시킵니다. 이러한 릴레이의 설정을 신중하게 조정함으로써 전력 시스템은 높은 수준의 오류 감지 및 격리를 달성하여 안정성을 유지하고 중단을 최소화할 수 있습니다.

복잡한 방사형 시스템에서 시간 지연 과전류 릴레이를 조정하는 것은 다중 소스에서 방향성 과전류 릴레이와 마찬가지로 어려울 수 있습니다.

Education

교육

JoVE Core

Electrical Engineering

전기공학

Unit 1

제1단원

System Protection

시스템 보호

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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, the apparent impedance drops. Under normal load, the current is low, so the measured impedance stays outside the relay’s tripping region and the line does not trip by mistake. When a fault drives the impedance into that tripping region, the relay operates.

Impedance relays are usually non-directional, but they can be made directional with a directional restraint or a modified relay design. Their reach is the fault detection range, and one relay can often be set with several zones. Each zone has a longer reach and a longer time delay, which helps coordinate protection across the line.

Ground fault impedance relays use line-to-neutral voltages and line currents. They can respond to single line-to-ground and double line-to-ground faults, but they do not detect line-to-line faults well. For line-to-line faults, phase relays are used instead. These relays use line-to-line voltages and the differences in line currents, so they are effective for line-to-line faults but less sensitive to single line-to-ground faults.

This split in relay sensitivity helps the right device respond to the right fault type. Modern digital impedance relays add self-monitoring, communication features, and precise timing adjustments. With careful setting coordination, power systems can detect faults quickly, isolate damaged sections, and stay more stable with fewer interruptions.

Impedance Relays for Fault Detection

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 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

Learn how impedance relays detect power line faults by measuring apparent impedance, using zones, and matching ground or phase relays to fault type.

Impedance Relays for Fault Detection | 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

Impedance Relays for Fault Detection

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