What is a hydraulic pitch control?
Hydraulic pitch control is a system where the blade angle is controlled by one or more hydraulic cylinders placed in the hub of the turbine.
Hydraulic pitch control is a drive system, which under emergency control is able to operate without an external power supply. Furthermore, hydraulic pitch control is not sensitive to vibrations, and failure safe operation is easily achieved with only a few non-electrical components.
The flow to and from the cylinders is controlled by a number of valves, in particular a proportional valve which is a valve where the opening area is controllable.
The energy to drive the hydraulic cylinders is supplied by a power unit placed in the nacelle, and the energy is transferred to the hub via a rotary union. This union is mounted together with the slip ring which transfers the electric control signals.
In the hub, the power from the nacelle is temporarily stored in hydraulic accumulators before released to the pitch system.
Hydraulic accumulators are, like electric accumulators, energy conservation devices where energy is stored by compressing a neutral gas such as Nitrogen. This fact that the energy is stored in a manner not requiring any electricity to be released, makes hydraulic systems extremely safe and reliable.
Why choose a hydraulic pitch system?
A hydraulic pitch system should be chosen because of its simplicity and ability to work under very harsh conditions. Hydraulic pitch control works under almost all weather conditions. The temperature span may vary from -25°C to +55°C without affecting the system's performance.
The system offers easy installation and high reliability due its rapid response and non-electrical high power emergency state.
As the fluid in the system has the ability to dampen structural vibrations and resonance power peaks/loads, it reduces the wear on e.g. Pitch bearings and increases the overall reliability of the turbine.
The hydraulic system contains no power electronics or vulnerable speed control drives with lots of components.
Hydraulic pitch control gives you the shortest possible stopping time in case of emergency stops. Instant stop can for instance be achieved with 5-9 degrees pr. second, giving a total stopping time of less than 10 seconds.
Hydraulic pitch control prompts low total cost of ownership
Easy mounting and low maintenance costs along with a long life span make hydraulic pitch control a good investment.
When producing larger series of wind turbines, manifold techniques are used. Mounting of such systems is easy and not particularly time consuming, as this approach only requires installation of very few components.
Hydraulic systems are by nature backlash free. Hence, the mechanical wear on the pitch control is minimal. This combined with high level of stiffness of the hydraulic system results in optimum performance with maximum damping. Particularly rapid changes in wing torque due to turbulence and high wind gusts are controlled and dampened, and not being transferred through the mechanical system thus preventing wear.