In a wind turbine, the gear unit's task is to step up the low speed of the rotor shaft through several gear stages to that of the output high speed drive shaft. The unit must be built for a 20-year working life in arduous conditions, a requirement that wind turbine gearbox manufacturers have struggled to meet. Gearbox failure is a serious problem in the wind industry.
The basic design of the Winergy test beds is nearly the same for all power classes: the gear units are clamped into place "back-to-back" so two can be tested at a time. The first unit operates as a speed reduction gearbox, delivering low speed, high torque power to the input shaft of the second gearbox in much the same way as delivered to a gearbox in a fully operating wind turbine in the field. A specific testing sequence is used for each gear type and the load is gradually increased -- and well beyond the actual rating in some cases. Prototype gear units are tested at double their rated capacity. Winergy's testing capacity of 14 MW suggests the company is taking a long term view. The largest gear unit sizes in the wind industry today are typically for use in turbines with rated capacities of no more than 5 MW.
The purpose of testing is to check the contact profiles of the gear teeth and their response throughout the load range. At the same time, various vibration, noise and temperature measurements are taken so the results can be recorded, archived and evaluated using sophisticated software. This enables a wide range of operating conditions to be delivered, including simulation of sudden gusts of wind.
Another task that is handled by the software is plant safety. Failsafe controls and monitors watch over the normal sequence of events and safety-related equipment on the test bed -- including several emergency stop circuits -- and initiate defined power-down (brake and/or coast down) if the vibration limits are reached, monitored by sensors in nine places.
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