Interlock basics

WHY  INTERLOCKS ARE REQUIRED?

1. PREVENTS HUMAN MISTAKES
2. INDEPENDENCY OF REQUIREMENT BETWEEN OPERATION OF CIRCUITS AND INTERLOCKING SHOULD BE KEPT IN MIND TO ACHIEVE HIGHEST POSSIBLE RELIABULITY.

INTERLOCKS

1. FOR BUS ISOLATON:  EACH BUS HAVING BUS ISOLATOR FOR EACH BAY.
2. FOR CB ISOLATION: CIRCUIT BREAKER HAVING BOTH SIDES ISOLATORS.
3. FOR LINE/ICT ISOLATION: LINE / ICT HAVING LINE ISOLATOR.
4. FOR BUS MAINTANENCE: EACH BUS HAVING BUS EARTH SWITCH.
5. FOR CB MAINTANENCE: EACH ISOLATOR HAVING EARTH SWITCH TOWARDS CB SIDE.
6. FOR LINE / ICT  MAINTANENCE: EACH LINE / ICT  HAVING LINE EARTH SWITCH. 

ISOLATORS

1. ISOLATORS ARE NO LOAD SWITCHES. THEY ARE NOT PERMITTED TO BREAK POWER CURRENT OR TO CONNECT DIFFERENT VOLTAGE SYSTEM.
2. MAKING OR BREAKING OF PARALLEL CIRCUITS IS PERMITTED.
3. AN ISOLATOR CONNECTED IN SERIES WITH A CB MAY BE OPERATED WHEN CB IS OPEN AND IF NONE OF ADJACENT EARTH SWITCHES IS CLOSED. EVEN IF ANOTHER ISOLATOR CONNECTED IN SERIES TO THE CB IS OPEN THE ISOLATOR IS NOT ALLOWED TO OPERATED UNLESS THE CB IS OPEN.
4. AN ISOLATOR CONNECTED TO A DUPLICATE BUSBAR OR AUXILIARY BUS MAY BE OPERATED IF

               i) NO LOAD IS CONNECTED AND NON OF THE EARTH SWITCH IS CLOSED.

                ii) A PARALLELING CIRCUIT TO THE ISOLATOR IS PRESENT. (ONLY THROUGH THE BUSCOUPLER FOR THE ISOLATORS THAT ARE CONNECTED TO THE TRANSFER BUS.

EARTH SWITCH

1. OPERATED ONLY IF THE ISOLATORS ON BOTH THE SIDES ARE OPEN.
2. EARTH SWITCHES WHICH CAN EARTH AN INCOMING LINE DIRECTLY OR THROUGH A CB CAN BE OPERATED IF AND ONLY IF THE LINE IS DEAD.