Operation of power systems incorporating fault current limiting devices

Power systems on large offshore plants such as Floating Production Storage Offloading (FPSO) must have minimal footprint and weight. This together with the move to all electric drives often results in the use Fault Current Limiters (FCL) to avoid exceeding the short-circuit current ratings of the electrical equipment. Pyrotechnic devices are often used and these operate within less than 4 milliseconds which is much faster than the circuit-breakers which need 50-70 milliseconds to open. Also the FCLs will operate only based on the current flowing through them, independent of the location of the fault which could be on a bus-section or somewhere on an outgoing feeder, even downstream of the breaker. Thus a feeder fault, correctly cleared by its breaker could result in separation of the main switchgear into two or more islands. It is necessary to take the operation of FCLs into account when defining the possible acceptable operation configurations in order to be able to maintain production after a serious fault. Recent experiences where the complete switchgear lineup was tripped for a single fault are not acceptable. Load-shedding algorithms must also be designed with FCL operation in mind. This will require consideration of multiple conditions during a sliding time window in order to define which loads must be tripped in order to avoid unnecessary production losses. Special care is required when defining the protection functions and setting the relays. Finally the operation of the gas turbine generators and the distribution of the load among different busbar sections will be reviewed.