Interlocking Relays in Txmission lines.

[busfault]

Hi guys
In our state in some of the stations we have interlock relays (zero,positive and negative sequence relays) in conjuction with distance protection and in some we don`t have these interlock relays.My question is how important are they and what do they do?
Thank you!!!

 

[busbar]

They may provide logic to establish varying operation of switchgear during a fault.

Partially related discussion at thread238-66404

One non-preducer-specific reference is IEEE Std C37.113-1999 Guide for Protective Relay Applications to Transmission Lines Description (only) at

http://standards.ieee.org/reading/ieee/std_public/description/relaying/C37.113-1999_desc.html