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

Differenzialrelais schützen Generatoren, Busse und Transformatoren.
In einem störungsfreien Generator halten identische Stromwandler das Relais inaktiv, da kein Strom durch die Betriebsspule des Relais fließt.
Ein interner Fehler, wie z. B. ein Phase-Masse- oder Phase-zu-Phase-Kurzschluss, stört dieses Gleichgewicht, verursacht Differenzstrom und löst möglicherweise das Relais aus.
Elektromechanische Differentialrelais funktionieren, wie Schwebebalkenrelais, wenn die Kraft einer Seite die der anderen übersteigt. Da keine zwei Stromwandler identisch sind, können bei externen Fehlern auch bei gleichen Strömen erhebliche Differenzströme auftreten.
Zum Schutz des Busses wird für jede Phase ein Differenzialrelais verwendet. Wird einer aktiviert, öffnen alle an den Bus angeschlossenen dreiphasigen Leistungsschalter.
Liegt kein interner Fehler zwischen den Stromwandlern vor, bleibt der Differenzrelaisstrom Null. Ein Busfehler erzeugt jedoch einen Differenzstrom ungleich Null, der das Relais auslöst.
Transformatoren, die größer als 10 MVA sind, verwenden Differenzialrelais zum Schutz.
Spezielle Adaptionen gibt es für Mehrwicklungstransformatoren und spannungsregulierende Transformatoren.

differenzialrelais

Differential Relays

Differenzialrelais schützen Generatoren, Sammelschienen und Transformatoren, indem sie elektrische Größen an verschiedenen Punkten vergleichen. Wenn ein Fehler auftritt, löst die Stromdifferenz zwischen den beiden Punkten die Aktivierung des Relais aus, wodurch der Leistungsschalter geöffnet wird. Unter normalen Bedingungen sind der in einen Generator eintretende (i_1) und der aus ihm austretende (i_2) Strom gleich. Wenn jedoch ein Fehler auftritt, werden diese Ströme ungleich und der Differenzstrom fließt in der Betriebsspule des Relais, wodurch das Relais auslöst. Ein elektromechanisches Differenzialrelais, auch als Waagebalkenrelais bekannt, funktioniert auf der Grundlage des Vergleichs elektromagnetischer Kräfte, die durch den Differenzstrom erzeugt werden. Das Relais löst aus, wenn die Kraft auf die Betriebsspule die Rückhaltekraft überschreitet. Die Bedingung für den Relaisbetrieb ist gegeben durch:

<img alt="Equation1" src="/files/ftp_upload/16167/16167_PT_Equation1.svg" style="height: 30px;">

Der Busschutz wird durch den Einsatz von Differenzialrelais zur Erkennung von Fehlern innerhalb der Buszone erreicht. Das Relais wird aktiviert, wenn die Summe der in den Bus ein- und austretenden Ströme nicht Null ist, was auf einen Fehler hinweist.

Der Differentialschutz für Transformatoren ist aufgrund der unterschiedlichen Wicklungen und Windungszahlen komplexer. Wenn der Transformator unter normalen Bedingungen ohne internen Fehler arbeitet, sollten die Primär- und Sekundärströme, angepasst durch die jeweiligen Stromwandler-Übersetzungszahlen, ausgeglichen sein. Im Falle eines internen Fehlers fließt der Differentialstrom jedoch durch die Betriebsspule des Relais und führt zu dessen Auslösung.

Bei Dreiphasentransformatoren müssen die Stromwandler korrekt angeschlossen werden, um Phasenverschiebungen auszugleichen, die durch die Transformatorwicklungen verursacht werden. Dadurch wird sichergestellt, dass die Sekundärströme in Phase sind, wodurch ein fehlerhafter Relaisbetrieb verhindert wird. Bei Y-Δ-Transformatoren sollten die Stromwandler auf der Y-Seite in Δ und die Stromwandler auf der Δ-Seite in Y angeschlossen werden.

Differentialschutzmethoden wurden für verschiedene Transformatorkonfigurationen angepasst, darunter Transformatoren mit mehreren Wicklungen, Winkelphasentransformatoren und Transformatoren mit speziellen Anschlüssen.

Differenzialrelais

Differenzialrelais schützen Generatoren, Busse und Transformatoren.
In einem störungsfreien Generator halten identische Stromwandler das Relais inaktiv, da kein ...

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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

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Directional Relays in Power System Protection

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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...

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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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