5 which is the mechanical input to speed increaser 3 the mechanical output of the speed increaser is the high speed shaft 4 which is connected to a high speed generator 2 the gear ratio of the gearbox 3 is selected to match the required speed of the low speed shaft 5 to that of the high speed generator 2 and shaft 4 the wind turbine tower structure is identified as 1 in the figure this structure is used to elevate the turbine and provides static and dynamic support for mechanical loads subjected to the up tower structure it is customary for the tower to have an entry door as shown at 9 and this door is vented to allow the passage of outside air into the tower in addition to the door an opening is placed 180 degrees from the door to allow for additional air to enter the tower at 13 the additional tower cutout is undesirable as it weakens the tower structure yet it is required to allow for adequate air entry into the tower 1 further in fig1 in the case of a variable speed wind turbine the generator is electrically connected to the power electronic control system 11 via electrical pendant cables 15 the same is true for a constant speed wind turbine except that the control system at the bottom of the tower 11 is more conventional electromechanical or power electronic switchgear rather than a variable speed converter the control system 11 sits on a platform 10 heat removal from the control system 11 is accomplished by heat sinks 19 shown at the top of the control.