Page 95 - Offshore Electrical Engineering Manual

82 CHAPTER 5 Generation and Distribution Switchgear and Transformers

TRANSFORMERS

Offshore distribution transformers are usually of either sealed silicon oil filled or
encapsulated resin types. Standard mineral oil filled types are too great a fire hazard
and askarel-based insulants are regarded as a health hazard due to the presence of
PCBs and the use of all such material was prohibited in most parts of the world in
the early 1990s.
Air cored types are not recommended offshore in external locations because the
salt-laden environment tends to lead to insulation problems even with good enclosure
IP ratings. The sealed silicon-filled type have the advantages that a faster repair can
normally be obtained and Buchholz type pressure sensing for winding faults can be
fitted. Being heavy devices, transformer weights, in particular, need to be checked
against switchroom maximum floor loadings. If a transformer is used to interconnect
the main system with the drilling system, the heating effect of SCR harmonics may
need to be considered.
High voltage transmission transformers in offshore wind farm substations are
covered in PART 6 Chapter 6.