Delayed current zeros in FPSO offshore units

Abstract

It is well established that when short-circuit occurs close to generators' terminals, the instantaneous value of the fault current through the circuit-breaker may not reach zero amperes for some considerable time, so called delayed current zero phenomenon. Therefore circuit-breakers may not be suitable to clear the fault under this condition. Today's floating production, storage and offloading (FPSO) units are very large in terms of installed generation capacity, in the range of 100 MVA, and in terms of number of medium voltage motors, many of them connected directly to the generation voltage level. This leads to a very favorable condition for the occurrence of delayed currents zeros in FPSO's electrical power systems. This paper presents the results obtained in the analysis for a typical FPSO electrical power system. The main objective of this analysis is to verify the presence of delayed currents zeros, the non-zero times and how the system operational condition and type of event may influence the results.