Switchgear main-tie-main closed-transition transfer design strategy for high levels of available fault current

Large offshore production platform designs are characterized by high levels of horsepower for driven equipment. It is common to design around an all-electric approach where a central electrical power plant is installed and few (if any) turbine or diesel engine drivers are included other than for generators. This approach leads to the use of relatively large transformers and to higher levels of available short circuit current. Distribution Main-Tie-Main switchgear configurations in such facilities are frequently operated in an open tie configuration to avoid excessive levels of short circuit current. If one of the main supplies needs to be removed from service, it is preferable to closed-transition transfer the affected loads to the other main supply through the tie breaker. During the closed-transition transfer period, the switchgear may be exposed to a high level of available short circuit current. This paper discusses this closed-transition transfer scheme and addresses safeguards that may be taken to mitigate the short circuit current risks during the transfer period.