# Parametric Selection of Optimized Epicyclic Gearbox Layouts for Wind Power Plant Applications
## 1 Introduction  
Energy is the keystone for the development of any civilization. However, the generation of energy comes at a price, as resources must be spent. As human civilization has developed using fossil fuels so far, the price of progress must be paid in the form of climate changes and global warming. The influence of these changes may be mitigated, reduced, or their rate slowed down by performing a change to renewable and, therefore, sustainable energy sources [1, 2, 3, 4, 5, 6]. Wind power has been historically known as a source of renewable mechanical energy, and nowadays, wind turbines are being built to harness wind power to produce electricity. Wind turbines also have the advantage that they can be used to provide electricity in areas that do not have access to an electric grid at all or need long-distance power lines that are very expensive to build, for example, in a developing country [7, 8, 9]. Furthermore, 700 kW turbines are most likely the largest size suitable for small island type grids, as with larger units, supply and maintenance costs begin to rise considerably [10]. The 700 kW wind turbine power plant is also the largest size that can be relatively easily broken down for transport and can be reassembled with a single large crane or helicopter. The power output is enough to supply a large village, or to provide extra power on industrialized locations with constant wind supply, and may be even coupled to a battery bank to harvest wind power during times of low demand [11, 12, 13, 14]. As the wind turbine is a machine extracting power from a fluid in motion [15; 16; 17], its primary efficiency is constrained to 59.3% of the energy of the incoming fluid according to Betz's law, and contemporary designs can extract up to 80% of this amount [18]. Further inefficiencies that are hard to mitigate, such as turbine rotor losses, generator losses, turbine blade losses, and power transmission losses [19; 20], point to the turbine gearbox as the primary component that can be used to improve the power efficiency of a wind turbine. The wind turbine is a machine that operates at a relatively low number of revolutions per minute; therefore, a multiplier gearbox is required to turn the generator shaft at a speed acceptable for power generation [21; 22; 23; 24; 25]. Historically, this was achieved with a multi-stage gearbox; however, these tend to be heavy, cumbersome, and require multiple stages as gear pairs are practically restricted to ratios of about 8:1 in a single stage, or 0.125 when operating as a multiplier. The gearbox performance may be enhanced with improved bearing systems [26; 27; 28], by increasing the accuracy and machining quality of the gears [29], and by switching to epicyclic gearboxes using planetary gearsets as its components. Epicyclic gearboxes offer considerable advantages, notably a reduced weight and increased loading capacity due to multiple gears in mesh at the same time [30; 31; 32; 33; 34]. Furthermore, single-stage gearboxes of this type may be built for gear ratios up to 12:1 (multiplication 0.0833), and even more may be achieved by opting for two, three, or even four carrier boxes. The downside of these advanced gearboxes is that they require specialized calculation procedures to establish whether the gearbox design is kinematically feasible and whether the box can operate as a multiplier with a satisfactory efficiency ratio. Due to their complex design, they also require the provision of optimal lubrication [35; 36]. The advantages of the application of epicyclic (planetary) gear trains in relation to conventional gear trains [37; 38] include reduced size and increased resistance to wear and tear [39]. The application of planetary gear drives has significantly expanded into various engineering products such as, but not limited to, drives and actuators in robotics, machine tool drives, vessel propulsion, railway vehicles, aircraft main drives, etc. [40; 41; 42; 43; 44; 45].