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Green | October 2011

Winds of change

In view of challenging conditions facing turbines, optimising seal life is critical to effectiveness of the system, says Anil Dony Braggs.

In the last few years wind turbine technology has changed. Previously they were stall machines and their position would shift only once every 10 minutes. Such turbines have been superseded by continuous pitch systems where the pitch, position of the nacelle and angle of the blades constantly changes in small amounts once every rotation, which could be on average 15 times per minute! This means that instead of six long strokes per hour, the turbine’s hydraulic actuator must now initiate 900 short strokes in the same period, 24 hours a day, seven days a week and for a targeted 20 year period.

CHALLENGES
Turbines have to operate 24x7: To optimise energy production, there is now a change in actuator technology. Instead of hydraulics producing 6 long strokes per hour they now have to give 900 short strokes in the same period.

Maintenance should be limited: Maintenance is difficult and expensive on land but offshore it is really tough. And when the windmill is switched off for maintenance, it is not producing energy and losing income. Also, operators are often penalised if supply targets are not met. So a primary objective is to minimise routine downtime while stoppages due to component failure are to be avoided at all costs.

Our company is a world leader in sealing technology and supplies a specially-engineered sealing configuration to AVN Energy, a leading hydraulic actuator manufacturer for wind turbines.Meeting the dynamic criteria due to constant movement of the actuator, the sealing system offers maximised seal life and contributes to minimal turbine maintenance requirements.

Our company was approached by AVN to jointly develop a sealing system to meet the challenging requirements of continuous pitch systems. The specified solution is a complex arrangement of seals ranging from O-Rings to specialist Turcon PTFE based geometries and Slydring in Orkot. The unique configuration is specially engineered to enhance lubrication and optimise friction characteristics while preventing any external leakage.

Seals within the hydraulic actuators are integral to its performance, and optimising seal life is critical to long term effectiveness of the total system. Seals must operate at 250 bars/ 3625 psi with constant pressure on the rod from behind and differential side loads that control positioning. Wear has to be minimised and dynamic movement that is continuous in short strokes needs to be facilitated. Temperature resistance is required down to -30°C/ -22°F as standard and to -40°C/-40°F in the Artic, with maximum temperature capability of 60°C/140°F.
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