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Breaker failure protection composition _ breaker failure protection startup process
Breaker failure protection is a critical safety mechanism in power systems designed to prevent widespread outages and damage to equipment when a circuit breaker fails to operate correctly after a protective relay has issued a trip command. This protection system identifies the failure of a circuit breaker by analyzing both the protection action information from the faulty equipment and the current status of the failed breaker. Once confirmed, it initiates the tripping of other related breakers within the same substation, thereby limiting the affected area and ensuring the stability of the entire power grid. It also helps avoid severe damage to critical components like generators and transformers, and prevents potential grid collapse.
The breaker failure protection system typically consists of three main components:
1. **Start-up Circuit**: This circuit is triggered by the trip relay of the faulty device and a fault detection component. It only activates the failure protection if the protection relay does not reset and the fault remains within the protected zone.
2. **Time Component**: Once the busbar protection is activated, the timing component begins its delay. This time must be sufficient to allow for the circuit breaker’s trip time and the return time of the protection relay (typically around 0.3 seconds), without interfering with normal fault clearance.
3. **Trip Circuit**: All circuit breakers connected to the busbar are linked through a common trip relay, enabling them to be tripped simultaneously when a failure is detected.
The start-up process of breaker failure protection involves a series of steps, as illustrated in the accompanying diagrams. When a fault occurs, the protection device sends a trip signal to the circuit breaker. If the breaker fails to respond, the failure protection system is activated. A time delay is then introduced, allowing enough time for the circuit breaker to act. If the fault persists, the system triggers the tripping of all other breakers on the same busbar, isolating the fault and preventing further damage.
To enhance the reliability of the system, an AND gate is used to ensure that the failure protection only activates when both the protection relay and the current presence conditions are met. The current detection should be set above the load current to ensure sensitivity. Additionally, low-voltage or zero-sequence overvoltage components may be added to improve the reliability of the trip circuit. These components are connected in series with the trip relays, forming a robust trip loop.
The system usually includes two levels of delay: a shorter one (delay I) that trips the busbar or sectional breakers, and a longer one (delay II) that trips all outgoing breakers with power. This ensures a controlled and effective isolation of the faulted section.
Since the failure protection and busbar protection often share the same trip circuits, they are frequently integrated into the same panel. This integration enhances coordination and reduces complexity in the overall protection scheme. Proper design and configuration of these systems are essential to ensure accurate and timely response during critical fault scenarios.