3.2.3. Failure analysis
The wind turbine system failure process is implemented using
the methodology developed by Billinton (1970). Each wind turbine
is modelled as a series of subsystems, for which a probability of
‘moving from an operating state to a failed or reduced operating
state’ is envisaged. The probability of shifting states is governed by
the component reliability, which is the probability that the
component performs satisfactorily for the specified time interval
Table 8
Cost inputs.
No Name Explanation Unit
1 Electricity price Unit electricity price d=MWh
2 CTV charter cost Charter cost of the CTV d=day
3 CTV technician cost Cost of the CTV technician d=year
4 CTV fixed cost Fixed cost of the CTV such as insurance, maintenance, etc. d=year
5 Helicopter charter cost Charter cost of the helicopter d=h
6 Helicopter technician cost Cost of the helicopter technician (may require training) d=year
7 OAV charter cost Charter cost of the OAV d=day
8 OAV mobilisation cost Mobilisation cost of the OAV d
9 OAV technician cost Cost of the OAV technician d=year
10 Jack-up vessel charter cost Charter cost of the jack-up vessel d=day
11 Jack-up vessel mobilisation cost Mobilisation cost of the jack-up vessel d
12 Jack-up vessel technician cost Cost of the jack-up vessel technician (high skilled) d=year
13 Jack-up vessel CAPEX Initial investment required to purchase the jack-up vessel d
14 CTV fuel cost Fuel cost of the CTV d=m3
15 Helicopter fuel cost Fuel cost of the helicopter d=m3
16 OAV fuel cost Fuel cost of the OAV d=m3
17 Jack-up vessel fuel cost Fuel cost of the jack-up vessel d=m3
18 Preventive maintenance cost Cost of materials and equipment required to perform the task d=turbine=year
19 Component repair cost Cost of each component repair (only OEM) d=repair
20 Port and operations cost Cost of port, repair dock, maintenance base, helipad, etc. d=year
21 Insurance cost Insurance of the wind farm d=year
Y. Dalgic et al. / Ocean Engineering 101 (2015) 211–226 217
t. In this context, the hazard rates hðtÞ, which are determined from
observed annual failure rates in operational history and expert
judgement, are utilised to calculate the reliability of the turbine
components. Time dependent hazard rates provide flexibility to
investigate the change of reliability throughout the simulated life
time. If constant hazard rates are employed, there will no change
in the reliability within the simulation period. In the simulation
block, a uniformly distributed random number, R, in the interval
0 to 1 is generated at each time step and then employed to
determine if a failure has occurred. In this context, if the generated
random number is higher than the reliability value of the component
at that particular time step, the component fails, otherwise
continues functioning. If a component has a higher hazard rate,
there is a higher probability that this particular components fails.
The turbines are modelled as a series of sub-systems; therefore,
any component failure causes entire turbine system failure. After a
failure is identified, O&M technicians are allocated to perform the
repair. The transfer system of the O&M technicians is defined by
the ‘Transportation type’. The allocation of the O&M technicians
and the actual O&M activity is explained in the operational
simulations section in detail.