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

차동 계전기는 발전기, 버스 및 변압기를 보호합니다.
무고장 발전기에서 동일한 변류기는 릴레이의 작동 코일을 통해 전류가 흐르지 않기 때문에 릴레이를 비활성 상태로 유지합니다.
위상-접지 또는 위상-위상 단락과 같은 내부 오류는 이 균형을 방해하여 차동 전류를 유발하고 잠재적으로 릴레이를 트리거합니다.
밸런스 빔 릴레이와 같은 전기 기계 차동 계전기는 한쪽의 힘이 다른 쪽을 초과할 때 작동합니다. 두 개의 변류기가 동일하지 않기 때문에 동일한 전류에서도 외부 오류 중에 상당한 차동 전류가 발생할 수 있습니다.
버스 보호를 위해 각 단계는 차동 릴레이를 사용합니다. 하나가 활성화되면 버스에 연결된 모든 3상 회로 차단기가 열립니다.
변류기 사이에 내부 오류가 없으면 차동 계전기 전류는 0으로 유지됩니다. 그러나 버스 오류는 0이 아닌 차동 전류를 생성하여 릴레이를 트리거합니다.
10MVA보다 큰 변압기는 보호를 위해 차동 릴레이를 사용합니다.
다중 권선 변압기 및 전압 조절 변압기에 대한 특수 적응이 존재합니다.

차동 릴레이

Differential Relays

차동 릴레이는 발전기, 버스, 변압기를 보호하기 위해 다양한 지점에서 전기량을 비교하는 데 사용됩니다. 오류가 발생하면 두 지점 사이의 전류 차이로 인해 릴레이가 작동하여 회로 차단기가 열립니다. 정상적인 조건에서는 발전기에 들어오는 전류(i_1)와 나가는 전류(i_2)가 같습니다. 그러나 오류가 발생하면 이러한 전류가 같지 않게 되고 차이 전류가 릴레이 작동 코일로 흘러 릴레이가 트립됩니다. 밸런스 빔 릴레이라고 하는 전기 기계식 차동 릴레이는 차동 전류에 의해 생성된 전자기력을 비교하여 작동합니다. 작동 코일의 힘이 제한력을 초과하면 릴레이가 트립됩니다. 릴레이 작동 조건은 다음과 같습니다.

<img alt="Equation1" src="/files/ftp_upload/16167/16167_PT_Equation1.svg" style="height: 30px;">

버스 보호는 버스 구역 내의 오류를 감지하기 위해 차동 릴레이를 사용하여 달성됩니다. 릴레이는 버스에 들어오고 나가는 전류의 합이 0이 아닐 때 작동하여 오류를 나타냅니다.

변압기의 차동 보호는 권선과 권선비가 다르기 때문에 더 복잡합니다. 변압기가 내부 고장 없이 정상 조건에서 작동할 때, 각각의 전류 변압기(CT) 비율에 의해 조정된 1차 및 2차 전류는 균형을 이루어야 합니다. 그러나 내부 고장의 경우, 차동 전류가 릴레이 작동 코일을 통해 흐르면서 트립이 발생합니다.

3상 변압기의 경우 CT는 변압기 권선으로 인한 위상 변화를 고려하여 올바르게 연결해야 합니다. 이렇게 하면 2차 전류가 동상이 되어 잘못된 릴레이 작동을 방지할 수 있습니다. Y-Δ 변압기의 경우 Y 측의 CT는 Δ로 연결해야 하고 Δ 측의 CT는 Y로 연결해야 합니다.

차동 보호 방법은 다중 권선 변압기, 위상각 조절 변압기, 특수 연결 변압기 등 다양한 변압기 구성에 맞게 조정되었습니다.

차동 계전기는 발전기, 버스 및 변압기를 보호합니다.
무고장 발전기에서 동일한 변류기는 릴레이를 비활성 상태로 유지합니다.

Education

교육

JoVE Core

Electrical Engineering

전기공학

Unit 1

제1단원

System Protection

시스템 보호

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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

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 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 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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