What are the conditions required for Successful Auto-reclosing of EHV Transmission Lines?

In this Article , we will explore the essential conditions for successful auto-reclosing of EHV transmission lines on fault. For the successful auto reclosing  Operation of overhead lines, following conditions should be satisfied:

1. Type of faults on overhead lines:
   Fault should be Zone 1 Single Phase Fault or Zone 2 Single Phase Fault with Carrier Receive.
   If the Zone 1 Single Phase Fault or Zone 2 Single Phase Fault with Carrier Receive occurs again in Reclaim Time (25 sec), AR will be attempted again.
   Zone 2 without Carrier Signal, Zone 3  covers a wider area. Here, a cautious method is needed. The longer distance can create doubts in figuring out the type of fault. In this zones, auto-reclosing is not carried out.
   
2. Position of ‘AR In/Out Switch’
   Auto-reclose should be in Service i.e ‘AR In’ position is chosen. The ‘AR In/Out Switch’ is commonly found on relay panels.
   Additionally, the ‘AR In/Out Switch’ is a safety tool which helps avoid any unplanned reclosure while maintenance of the Line is in progress, thereby keeping personnel safe and lowers the risk of damage to equipment.
   
3. CB Ready Signal:
   The CB Ready Signal coming from the Circuit Breaker consists of Spring Charge and SF6 ok.
   It indicates that the CB is ready to Close and the same needs to be given to the Distance Relay for the Auto-reclosing function
   
4. AR Block/86 Operated Signal:
   AR block can be activated by different reasons. These include certain grid conditions, protection scheme logic, or outside commands.
   There should be no AR Block (86 Operated) to Distance Relay.
   
5. CB Status:
   CB Close/Open Status should be available to the Distance Relay.
   

For other Faults, CB not Ready, AR Out of Service, CB Status not available, there will be Auto-reclose Lockout i.e. the Relay will issue a Three Phase Trip.