3.2.4.1. If the ‘Transportation type’ is a CTV/helicopter. These
transportation systems are assumed to be occupied by the maximum
number of technicians defined by the number of technicians for each
transportation type at the beginning of each shift. When the failure is
repaired, same technician team continues to do preventive maintenance
(if required/applicable), otherwise stays in the wind turbine. The teams
are not allocated to different wind turbines in a single shift. CTVs are
allocated dynamically during the operating shift. In this context, Fig. 2
shows the CTV and technician allocation order and the dependencies
between simultaneous operations in a repair day. It is aimed to sustain
the power productivity at highest level; therefore the capability of
completing the repair task in a single shift is the most important
consideration in the CTV allocation. If there are more than one CTV that
can complete the task in a single shift, it is targeted to use minimum
number of vessels; therefore it is prioritised to utilise a CTV which is
already in the offshore wind farm. However, at the beginning of a repair
shift, none of the CTVs would be allocated; therefore the number of
CTVs in the wind farm would be zero. In this case, having the maximum
number of working hours will be the consideration; thus, the number of
turbines, which can potentially be visited by this particular CTV, can be
maximised. When all the explained priorities are taken into account, the
CTV with maximum number of working hours will be allocated at the
beginning of the shift, and because this CTV will be in the wind farm, it
will again be allocated for the subsequent repairs until that particular
CTV runs out technicians or the number of visits becomes equal to the
‘Maximum visit per CTV’ value.
Helicopter operations are simulated after the main CTV operations,
however the repair process is simulated concurrently to
other repair operations. Helicopter is only utilised if a number of
criteria are met in order to represent the current operational
practices. In a single shift, the helicopter can perform visits only to
the turbines that have not been visited by any CTV (either due to
high number simultaneous failures or higher accessibility criteria
for the helicopter). In this case, the helicopter is utilised for the
repairs subject to having remaining flight hours in the year and the
site being accessible.
3.2.4.2. If the ‘Transportation type’ is a OAV. OAV repairs are
performed sequentially as soon as a failure of this category occurs.
After the first failure is simulated, an OAV is mobilised. Once the
mobilisation time is completed, the repairs can be performed subject
to the ‘Maximum operational wind speed’ and ‘Maximum operational
wave height’ limits of the OAV. The OAV remains in the wind farm for
the duration of the charter period, but repair work and/or travels
between wind turbines are only carried out during daylight hours and
when climate conditions allow. Any unfinished maintenance at the
end of charter period remains incomplete until another vessel is
mobilised.
3.2.4.3. If the ‘Transportation type’ is a jack-up vessel. Jack-up vessel
repairs are performed sequentially as soon as a failure of this
category occurs. After the first failure is simulated, a jack-up vessel
is mobilised. Once the mobilisation time is complete repairs can be
performed subject to the ‘Maximum operational wind speed’ and
‘Maximum operational wave height’ limits of the jack-up vessel.
The jacking-up/down operations are determined by wave height
and wind speed at sea level values, whilst the main repair
operation is performed subject to wind speed at hub level
criteria. The jack-up vessel remains available for the duration of
the charter period and repair work and/or travels between wind
turbines or to port to re-supply are only carried out when climate
conditions allow. Any unfinished jobs at the end of charter period
remain incomplete until another vessel is mobilised.