The optimum design of the medium voltage (MV) cables consists in finding the best compromise between the initial cost of the cables and the total energy loss of the system.
For this reason we design wind farms with a radial network, and section of the cables decreasing from substation to the most faraway point of the wind farm: the lesser the distance from the substation, the greater the amount of energy carried by the cables.
Furthermore, the resistance of the cable depends on his temperature, and the temperature depends on the current.
Normally cable section is decided after an iterative process: cable section depends on the prospective short circuit current, which is related to the cable section, voltage drop and losses and last but not least the cost of the cable itself.
To simplify the problem one of the simplifications is to consider all the WTGs exposed to the same wind speed for the same number of hours. This hours will be determined by the Weibull distribution of the wind farm.