These relays continuously monitor the health of the trip circuit to ensure that the breaker can successfully trip when required.
A faulty trip circuit can prevent a protection relay (e.g., 87B, 87L, 50/51) from operating correctly. Trip Circuit Supervision Relays detect these issues in advance to prevent system failure.
Why Are They Used with the 86 Master Trip Relay?
The 86 Master Trip Relay is crucial for isolating faulty equipment. If the trip circuit wiring or coil is defective, the 86 relay may not successfully trip the breaker.
➡️ Trip Circuit Supervision Relays (95/195/295) are installed to:
✅ Continuously monitor the trip coil, wiring, and breaker’s health.
✅ Alert operators via alarms or indication lights if any fault is detected.
✅ Ensure that when the 86 Master Trip Relay issues a trip command, the trip circuit is healthy and capable of functioning.
Working Concept:
- Healthy Condition:
- The Trip Circuit Supervision Relay constantly sends a small current (DC voltage) through the trip coil circuit to check continuity.
- If the circuit is intact, no alarm is triggered.
- Fault Condition:
- If the trip coil is open, disconnected, or has a broken wire, the Trip Circuit Supervision Relay detects this fault.
- It triggers an alarm or indication to alert the operator.
- During Fault Trip Operation:
- If the protection relay (e.g., 87B) sends a trip signal to the 86 Master Trip Relay, the Trip Circuit Supervision Relay ensures the trip path is clear and operational.
Example in a Busbar System:
➡️ A 220kV busbar has:
- Incomer 1, Incomer 2, Feeder 1, and Feeder 2.
- An 86 Master Trip Relay is used for bus protection.
- Trip Circuit Supervision Relays (195/295) are installed to monitor each breaker’s trip circuit.
Scenario:
✅ A fault occurs in Zone 1 (Incomer 1 area).
✅ The 87B relay signals the 86 Master Trip Relay to trip all Zone 1 breakers.
✅ The Trip Circuit Supervision Relay verifies the trip circuits are intact before the 86 relay trips the required breakers.
➡️ If one trip coil was faulty, the supervision relay would have already raised an alarm before this critical moment — ensuring immediate action can be taken.
Key Takeaway:
- 95/195/295 Trip Circuit Supervision Relays provide an early warning system for trip circuit faults.
- When combined with the 86 Master Trip Relay, they ensure reliable system protection by identifying potential failures before they cause major issues.