1. Supervision Relay – Why It's Used in HT Panels
A supervision relay monitors the health of auxiliary circuits (like trip circuits, closing coils, control wiring, etc.) in an HT panel.
Purpose:
Trip Circuit Supervision - Ensures the trip coil circuit is healthy.
Fault Prevention - Detects issues like open trip coils or blown fuses before an actual fault occurs.
Alarm & Indication - Provides alarms for faulty conditions.
System Reliability - Increases system uptime and safety.
2. Feeder Protection Relay
A Feeder Protection Relay protects outgoing feeders from electrical faults such as:
Protections Provided:
Overcurrent (O/C)
Earth Fault (E/F)
Short Circuit
Directional Protection (in ring mains)
Breaker Failure Protection
4
Types:
Electromechanical (old)
Static
Numerical (modern & preferred) - Microprocessor-based
3. Lockout Relay (86 Relay)
A Lockout Relay is a master trip relay used to isolate the system in critical fault conditions. Once operated, it locks out the breaker until it is manually reset.
Key Functions:
Receives trip signals from protection relays.
Sends a final trip to the breaker.
Activates alarms.
Prevents automatic reclose until manual inspection and reset.
Application:
Transformer protection (e.g., via Buchholz or Differential relay)
Generator or feeder trip logic
Busbar protection schemes
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