Winds of change: Sealing in wind turbine actuators

Winds of change: Sealing in wind turbine actuators

Winds of change: Sealing in wind turbine actuators

Winds of change: Trelleborg Sealing Solutions solves the sealing challenge within wind turbine actuators

Trelleborg Sealing Solutions supplies a specially engineered sealing configuration to AVN Energy A/S, a leading hydraulic actuator manufacturer for wind turbines. Meeting the dynamic criteria due to constant movement of the actuator, the sealing system offers maximized seal life, contributing to minimal turbine maintenance requirements.

Stall machine turbines being replaced by continuous pitch systems has put extreme demands on hydraulic actuators. The position of stall machines would shift only once every ten minutes but in continuous pitch wind turbine systems, the nacelle and angles of the blades constantly change in small amounts once every rotation, on average 15 times per minute. This means that instead of producing six long strokes per hour, the turbine’s hydraulic actuator must now initiate nine hundred short strokes in the same period, 24 hours a day, seven days a week, for a targeted 20-year period.

“Customers have high expectations from our products, and the number one requirement of the wind turbine manufacturers is reliability,” says Poul Kristensen, Export Sales Manager at Denmark based AVN Energy A/S, one of the world’s leading suppliers of actuators for wind turbines. “Maintenance of turbines is difficult and costly. On land, it is hard enough, but offshore it is really tough. And when the windmill is switched off for maintenance, it is not producing energy and losing income. On top of that, operators are often penalized if supply targets are not met. So a primary objective for them is to minimize routine downtime, while stoppages due to component failure have to be avoided at all costs.”

Picture is a diagram of a typical windmill showing position of the actuator

The seals within the hydraulic actuators are integral to its performance, and optimizing seal life is critical to the 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 minimized 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.

Having worked with Trelleborg Sealing Solutions on stall machines, AVN approached it 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 optimize friction characteristics, while preventing any external leakage.

Picture shows actuator from AVN Energy A/S

Extensive testing concentrated on all aspects of assembly design in conjunction with the seal configuration. The aim of this was to maximize service life and achieve the operators’ 20-year target for turbine life with as little as possible maintenance. Some of the seals within the system are expected to achieve that time span without replacement, but it is impossible to guarantee it for all.

The hydraulics are therefore designed for easy exchange of the seal set. This is mounted in a module that can be quickly bolted on and off. The minimum life expectancy of the sealing configuration, allowing for the seal that has the shortest predicted life, is seven years, but replacement is recommended after five. Other than this, and routine rod replacement, the actuators should run without maintenance except for the systematic checking that the operators do for any leakage or loss of pressure.

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