Description: The ANSI 87L relay provides high-speed differential protection for transmission lines, ensuring precise fault detection and isolation.
What is ANSI 87L?
The ANSI 87L relay is a Line Differential Protection Relay designed to protect transmission lines and feeder circuits. It operates using the differential protection principle, comparing current at both ends of the protected line.
Where is ANSI 87L Used?
- Transmission Line Protection (long-distance power transfer lines)
- Feeder Line Protection (in distribution networks)
- Cable Protection (for underground or submarine cables)
- Hybrid Circuits (a mix of overhead lines and cables)
How Does It Work?
- The 87L relay measures the current at both ends of the protected line.
- Under normal conditions:
- Current entering the line = Current leaving the line
- During a fault within the protected zone:
- Current entering ≠ Current leaving (due to leakage or short circuit)
- The relay detects this imbalance and trips the associated circuit breakers to isolate the faulty section.
Real-World Example (Line Fault Scenario):
Imagine a 132kV transmission line connecting two substations.
- Station A measures 800A current entering the line.
- Station B measures only 700A current leaving the line.
- The 100A difference indicates a fault in the protected section.
The 87L relay detects this imbalance and trips the circuit breakers at both ends to isolate the faulty line segment.
Key Benefits:
- Fast and selective fault detection minimizes power disruption.
- Ideal for protecting long transmission lines with complex network conditions.
- Provides high stability even during external faults or system disturbances.
How Do Substations Exchange and Compare Currents in 87L Protection? Let’s now
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