- Backup Relay Definition: A backup relay is an additional relay system that operates if the main relay fails, ensuring continued protection.
- Function of Backup Relay: The primary function of a backup relay is to trip the circuit breaker when the main relay fails.
- Reasons for Main Relay Failure: Main relays can fail due to mechanical defects, power supply issues, or problems in the CT/PT circuits.
- Importance of Backup Relay: Backup relays provide an extra layer of reliability, essential for protecting expensive and high-voltage equipment.
- Operation of Backup Relay: Backup relays are designed to act slower than main relays, stepping in only when the main relay fails.
A power transformer is expensive plant, and so is an extra-high-voltage line. The main transformer protection can fail. A backup relay is a second scheme whose job is to trip the circuit breaker if that main relay does not. The main relay can fail for the following reasons:
- Mechanical defect of moving parts of the main relay,
- Failure of DC power supply to the relay,
- Failure of tripping pulse to the breaker from relay,
- Failure of current or voltage to the relay from CT or PT circuits etc.
In such situations, a backup relay provides another line of protection. Backup relays must have separate systems from the main relay scheme. This ensures they operate if the main relays fail.
Sometimes, main relays must be disconnected for maintenance or troubleshooting. Backup relays allow this without interrupting the equipment or circuit. During this time, the backup protection scheme ensures the system remains protected.
Since backup relays are the second line of protection, they act slower than main relays. This ensures they only operate when the main relay system fails.
