Description: The ANSI 96 BB/LBB Relay is a specialized trip relay designed to provide Busbar Protection (BB) and Local Breaker Backup (LBB) protection, ensuring fast fault isolation in case of primary protection or breaker failure.
Where is the ANSI 96 Relay Used?
The 96 BB/LBB Relay is typically employed in:
✅ Busbar Protection Panels → For tripping multiple breakers during a bus fault.
✅ Breaker Failure Protection Schemes → For backup tripping when a breaker fails to operate.
✅ Transformer Panels → To isolate faulty transformers connected to the busbar.
✅ Line Panels → For isolating faulty lines during breaker failure conditions.
Key Functions of the ANSI 96 Relay:
1. Busbar Protection (BB Function):
- Detects busbar faults and sends a trip command to all connected breakers to isolate the faulty bus section.
- Works with protection relays like 87B (Busbar Differential) to ensure fast clearance.
Example:
In a 220kV busbar system, if a bus fault occurs, the 96 BB relay trips all associated breakers to isolate the entire bus section, preventing system-wide disruption.
2. Local Breaker Backup (LBB Function):
- Provides backup protection when the primary breaker fails to trip during a fault.
- After a short delay, the LBB relay sends a trip command to the upstream and downstream breakers to clear the fault.
Example:
Suppose a 132kV breaker fails to trip during a fault. The LBB relay:
➡️ Detects the failure.
➡️ Sends a trip signal to the surrounding breakers (e.g., incomer or adjacent breakers) to isolate the faulty section.
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How Does the LBB Relay Detect Breaker Failure?
The LBB relay activates under these conditions:
✅ Trip signal given to the breaker.
✅ Breaker position (auxiliary contacts) shows breaker still closed after a set time delay.
✅ The LBB relay then issues a backup trip command to the relevant breakers.
Key Benefits:
- Ensures fast busbar fault isolation to prevent widespread outages.
- Provides reliable backup protection for breaker failure conditions.
- Minimizes damage to equipment by ensuring faults are cleared quickly.
- Essential in systems requiring high stability and minimal downtime.
Difference Between Busbar Protection (BB) and Local Breaker Backup (LBB) Protection, Learn More
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