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What is the breaker failure protection _ breaker failure protection principle
Breaker failure protection is a critical safety mechanism used in power systems to ensure that, in the event of a circuit breaker failing to trip when it should, the fault is still effectively isolated. This protection system works by detecting the failure of the circuit breaker after the relay protection has issued a trip command but the circuit breaker does not respond. By analyzing the protection action information and the current status of the circuit breaker, the system identifies whether a failure has occurred.
Once a failure is detected, the breaker failure protection initiates a faster response than traditional backup methods, isolating other related circuit breakers within the same substation or power plant. This helps to minimize the affected area, reduce the risk of widespread outages, and maintain the stability of the entire power grid. Without such protection, faults could lead to severe damage to equipment like transformers and generators, or even cause a total grid collapse.
In high-voltage power systems—especially at 110kV and above—breaker failure protection plays a crucial role. When a fault occurs on a transmission line, transformer, or busbar, and the associated circuit breaker fails to open, the breaker failure protection is triggered. Common causes of such failures include issues with the trip coil or the operating mechanism of the circuit breaker. To address this, power systems are equipped with backup protection schemes. However, relying solely on far-backup protection from adjacent components can be problematic due to sensitivity issues and longer response times, which may worsen the fault's impact.
To overcome these challenges, modern power grids often implement dualized protection systems for critical lines, especially at 220kV and above. These systems provide two independent sets of full-line fast protection, reducing the chance of protection failure. Additionally, breaker failure protection is specifically installed to handle cases where the circuit breaker itself fails to operate as intended.
The principle behind breaker failure protection involves several key components: a voltage blocking element, a start-up circuit composed of both protection action and current discrimination, a time delay component, and a trip output circuit. The start-up circuit is essential for ensuring accurate operation, requiring double confirmation to avoid false trips caused by contact issues or accidental triggers. It typically uses an automatic trip signal from the circuit breaker’s own outlet, combined with auxiliary relays to confirm that the circuit breaker has not tripped.
The current discrimination element checks for residual current after a fault occurs, indicating that the fault remains unremoved. The time component acts as a buffer, ensuring that the protection does not activate prematurely. It works in conjunction with the start-up circuit using an AND logic gate to prevent false triggering. Voltage blocking elements, such as low voltage, negative sequence voltage, and zero-sequence voltage relays, are also used to enhance reliability.
Overall, breaker failure protection is a vital part of modern power systems, offering a near-backup solution that ensures faults are cleared quickly and safely, protecting both equipment and grid stability.