Interlocking System (Exercise 14)
general goal
interlocking prevents undesired operation states and demage of equipment
feeder level
feeder level interlocking uses information available in the feeder
objective: do not switch non zero currents with isolator
rule: do not switch isolators when circuit-breaker is closed
station level
station level interlocking uses information available in a substation
feeder equipment is rated for currents refering to the nominal values of the connected branch (e.g. 1000 A)
busbar conductors and busbar coupling may cover much higher currents (e.g. 3500 A)
objective: prevent overload of feeder equipment (switches, conductors) => prevent bus bar coupling with isolators
rule: do not close a second bus bar isolator in a feeder if the busbar coupling is not closed
control center level
the following interlocking conditions can only be checked in the control center because they relate to more than one substation
- grounding
objective: prevent grounding of energized circuits
- switching off load
objective: prevent unintended disconnection of loads
In the control center the local interlocking conditions (mentioned above) are also checked:
- SCADA prevents operator from sending undesired signals to substation
- operator may unlock ("Entriegeln"-Button) to send the signal anyway
- local interlocking equipment refuses switching and returns alarm message
remarks
the interlocking rule is sometimes stricter than needed to fullfill the objective