Generating steady shaft speed on a wind turbine means constantly adjusting the pitch of each blade to accommodate wind variations. The blades connect to a huge hub mounted to a shaft that turns a gearbox and a generator. Best turbine efficiency calls for a continuous pitch control on the blades. Blade pitch is powered by either an electric or hydraulic drive. Electrical pitch control uses slip rings to conduct power to large powerful motors rotating in the hub, which require reliable battery backup. Hydraulic systems, on the other hand, use a rotary union to deliver hydraulic power to the drive motor. The advantage of hydraulic control is that its power density is higher than electrical equipment and it needs fewer components, making for a simpler system and lower wear on moving components.
The most important part of the hydraulic unit is the high pressure rotating union allowing the hydraulic liquid to be pumped from the stationary pressure accumulator into the rotating hub to reach the adjustment cylinders. The requirements for this small component are extremely high: it must safely seal the static part from the rotating part; it must guide the hydraulic medium in a safe manner; it must be installed easily; it must be made of materials which can resist adverse environmental conditions; and it must have a long service life, even with contamination of the medium.
Rotating unions from Deublin, the market leader in this field, meet these requirements. They are based on a hydrostatic sealing principle with controlled bypass flow to ensure that the sealing faces are lubricated on a permanent basis, a feature contributing to durability. They are available in single- to multi-channel designs and, depending on the model, generate up to 250 bar hydraulic pressure, as well as having a central channel for sensor technology or connection to a slip ring. Furthermore hydraulic systems equipped with a Deublin rotating union are secured against oil leakage, so there are no environmental implications.
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