Auto recloser function is used for transmission line protection system to avoid tripping during transient fault of the line. The function is available in the distance protection relay however separate auto recloser relay is also available for using the function.
Auto Recloser Relay Function:
We know that the distance protection relay is used to protect the transmission line during any fault of the line. There are many types of fault occurred in the transmission line, some of the faults are transient which occurred for some moment and clear the fault automatically. Lightning is the perfect example of transient fault. During lightning on the transmission system, the Phase to earth fault occurs and which is in transient nature.
Whenever any phase to earth fault occurred in the transmission line, the distance relay detects the fault and it will trip that phase of the circuit breaker of the line to isolate the fault. Except for that phase, other healthy phases will remain close position. The opened CB pole of the faulty phase is again close after 1 second by an auto recloser relay. If the fault is in transient nature, in that case, the fault may clear within 1 second and after the closing of the CB pole, the line will hold or power will remain flowing.
If the fault is persisting in the transmission line, then the distance relay detects the fault again and it will trip all the 3 phases of the circuit breaker to isolate the line permanently from the substation bus.
In this auto reclose function, the tripping or outage of the transmission line can be avoided at the time of the transient fault.
Blocking Mode (AR Block):
Before sending the close command during the auto reclose, the relay will check the following status, if the same are not satisfied then the AR relay will not send the close command and it will be shifted to AR Block mode.
- The CB must be in healthy condition. If the CB unhealthy status is received by the AR relay it will block the AR function.
- If the fault detects in SOTF or Zone 3 or Zone 4, in that case, the relay will block the AR function.
Lockout mode (AR Lockout)
Lockout mode is the important function in the Auto reclose relay. In the following condition, the AR lockout function will activate and it will trip the circuit breaker directly.
- If any AR block command is received after the tripping of any phase.
- If the AR function is in progress mode for any single-phase fault, during the reclaim time, if any fault is detected by the other phase, the AR lockout function will work.
Auto recloser reclaims time is the duration when the AR relay will not accept any reclose command. When auto reclose function is started for any single-phase, the reclaim time will start and after the reclaim time, the AR relay will be ready for accepting another auto reclose command. The reclaim time depends on the fault incident, CB spring charging time and TZ2 zone delay time.