Page 357 - Offshore Electrical Engineering Manual

344 CHAPTER 6 Notes on Offshore Renewable Energy Substation Platforms

Electric hoists/davits will be required for loading supplies from the small service
boat but larger supply boats would need to use a crane. If the substation platform is
well out to sea, consideration would need to be given to providing a helideck.
Sacrificial cathodic protection anodes should be fitted to the jacket structure and
the splash-zone will be made of thicker metal with a special paint coating system as
with any offshore structure.

HAZARDS

The biggest hazard is likely to be the two large 33 /132 kV step-up transformers,
which are currently oil-filled with separate coolers. There is a risk of explosion if
an internal winding (interturn) fault causes an explosion though generation of gases
from the hot oil. For environmental reasons, relief valves should be provided to dis-
charge the oil pressurised by the hot gases into a dump tank. Assuming that trans-
formers are geographically separated, the dump tank would only have capacity for
one transformer failure. However, it is not considered acceptable to allow the trans-
former oil to be dumped into the sea apart from in the event of catastrophic loss of
the substation platform. Therefore use of H120 fire barriers between the transform-
ers, although beneficial, may not be sufficient without physical separation. Typical
transmission transformers weigh 135 tons (108 tons dry) and installation of topsides
would normally be complete with the main transformers in ‘wet’ condition.