TIE LBB IN ONE AND HALF BREAKER SCHEME
GENERALLY IN 400 KV SWITCHYARD ONE AND HALF BREAKER SCHEME OR ONE AND HALF BREAKER BUS ARRANGEMENT IS USED. THIS ARRANGEMENT HAVE SEVERAL ADVANTAGES. IN THE UPCOMING VIDEO WE WILL DISCUSS IN DETAIL ABOUT THIS BUS ARRANGEMENT. IN THIS SCHEME THERE ARE 3 NOS.OF CBs IN SERVICE FOR EACH SET OF 2 FEEDERS IN ONE DIA. TEE DIFFERENTIAL PROTECTION IS ALSO REQUIRED FOR THIS TYPE OF BUS ARRANGEMENT AS DISTANCE AND BACKUP OVERCURRENT/EARTHFAULT PROTECTION IS TAKEN AT LINE SIDE CT. FOR PROTECTION OF DIAGONAL TWO NOS. Of #TEE-DIFFERENTIAL RELAYS ARE INSTALLED. BESIDES REGULAR LBB PROTECTION WHICH GENERALLY TRIP ALL OTHER SOURCE SIDE CB TO CLEAR THE FAULT, A SEPARATE TIE LBB PROTECTION IS USED IN EACH DIAGONAL. TIE LBB INITIATES BY MAIN 86 / 21 RELAYS AND ISSUE TRIP COMMAND IF TIE CB FAILS TO CLEAR THE FAULT.