Description: ANSI 87CU relay provides fast and reliable busbar differential protection, ensuring fault detection and isolation in busbar systems.
🔎 What is ANSI 87CU?
The ANSI 87CU relay is a Busbar Central Unit used for differential protection in busbar systems. It detects internal faults within the busbar zone and trips the breakers to isolate the faulty section.
🛠️ Where is ANSI 87CU Used?
✅ Busbar Protection Systems (in substations)
✅ Main Incomer Bays (to protect incoming power sources)
✅ Feeder Bays (to monitor outgoing circuits connected to the busbar)
✅ Transformer Bays (when transformers are part of the busbar network)
⚙️ How Does It Work?
- The 87CU relay compares the sum of currents entering and leaving the busbar.
- Under normal conditions:
➡️ Incoming Current = Outgoing Current - During a busbar fault:
➡️ Incoming Current ≠ Outgoing Current - The relay detects this imbalance and instantly trips the associated circuit breakers to isolate the faulty section.
🔋 Real-World Example (Busbar Fault Scenario):
Imagine a substation busbar with:
- 2 Incoming Lines (from generators or transformers)
- 4 Outgoing Feeders (to supply different loads)
If one of the busbar connections has a short circuit, the 87CU relay will:
✅ Detect the unbalanced current flow.
✅ Trip only the faulty section’s breaker to maintain system stability.
🔍 Key Benefit:
The 87CU relay ensures fast fault clearance with minimal disruption, making it essential for protecting critical power distribution systems.
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