Aging Wind Turbines: Entending turbine life with proper hydraulic systems, filtration & condition monitoring

As increasing numbers of wind turbines move out of their manufacturers’ warranty period, more and more third-party maintenance engineers will be required to provide independent advice to wind farm operators. In particular, third-party technical capacity will be required for component inspections, repairs, and refurbishment—especially for critical parts such as gearboxes and blades.

With hydraulic systems representing a substantial part of each turbine (yaw and pitch control, and brake control), it’s important operators and prospective maintenance providers are aware of the potential problems that could arise as parts wear, as well as how to implement an effective predictive maintenance program.

Equally important is the development of critical systems that are as reliable and long lasting as possible to minimize failure and wear rates, and to reduce the need for routine maintenance. There’s also a growing request to minimize the amount of maintenance carried out at the top of each turbine tower by modularizing key operational units, and/or moving them to ground or sea level. This is driven not only by a need to improve cost-efficiency, but also the need to protect the health and safety of maintenance personnel.

Hydraulic technology
Safety and cost-efficiency are a strong force behind the trend for wind turbine designs to operate at optimum levels of efficiency and with very little manual intervention. To achieve this goal, many manufacturers are turning to the latest generation of hydraulic technology. For instance, manufacturers are increasingly integrating the latest hydraulic technology into nacelles to control the pitch of the blades and the yaw of the nacelle. Use of this technology maximizes a turbine’s power generating efficiency and, just as importantly, protects the equipment in high winds. It’s also used in low-maintenance hydraulic gearboxes, helping wind farm operators to reduce costs considerably.

The use of hydraulic cylinders in pitch control systems allows the angle of the rotor blades to be varied slowly and precisely through a cam action, optimizing generating output. The blades are either turned into the wind to increase the rotational speed if the wind speed falls, or out of the wind if the wind speed increases. This causes the rotational speed of the blades to decrease to protect the turbine from damage, and is typically achieved by installing three pitch control systems in the hub of the turbine, one for each blade.

Similarly, the yaw or rotational position of the nacelle can be continually adjusted to further boost operating efficiency of wind turbines. In the same way output is optimized by tilting the angle of the blades so they are facing the wind, the nacelle must also be rotated horizontally about the axis of the tower, in response to changing wind direction. In comparison with other methods, such as electromechanical control, hydraulically powered yaw control systems are able to offer a simple, compact direct-drive, which also reduces maintenance requirements and costs.

Hydraulic protection
Technology is allowing wind turbine manufacturers to develop systems that enable improved operating efficiencies. However, as with any application, protection is important. Within a turbine, hydraulics must be protected from potential particulate and water contamination, the primary cause of failure in lubricated and hydraulic equipment. Indeed, it’s vital to employ a range of effective filtration and condition-monitoring solutions if reliable operation and minimal operating costs are to be achieved.

Effective inline filtration technology is an essential element to capture particles before they reach sensitive components in all large capacity turbines, including those that have alternative methods of pitch and yaw control (such as electromechanics). Gearbox problems typically account for the majority of unplanned maintenance requirements. And, with turbine gearboxes required to gear up the low-speed input shaft to provide a high-speed output for a turbine, the filtration for both lubricating and hydraulic fluids is crucial.

Where hydraulic control systems are used, effective filtration technology is particularly important for extending maintenance intervals and increasing the reliability of pitch and yaw systems. A comprehensive range of filtration technology has been developed for filtering out particulate and water contamination from hydraulic fluid to just a few microns. It’s vital to eliminate the risk of precision-engineered system components (such as cylinders, accumulators, or valves) suffering from reduced performance levels and premature failure—which can ultimately reduce the efficiency of a wind turbine and raise costs for operators.

Considerable care must be taken, however, when selecting and specifying filtration systems to prevent restriction of the fluid flow and reduction of the efficiency of the hydraulic circuit. By correctly sizing these devices to accommodate the overall operating conditions, the risk of any pressure loss across filters (and associated problems, such as increased energy consumption and heat generation) can be avoided.

Modern filter materials now offer unrivalled strength and dirt holding capacity while reducing resistance to flow, thanks to advances that modified the composition and construction of standard glass fibre materials. The latest fluid filtration technology is also effective at removing contaminants that find their way into a hydraulic system. But, it’s still advisable to record and monitor contamination levels using particle-counting technology, so maintenance is scheduled before any damaging problems occur. Look for the latest portable analyzers, which use a process called light obscuration, light blockage, or light extinction. They quickly and accurately measures contamination levels in hydraulic fluids.

A particle detector can also be built into the hydraulic system, including the lubrication or power transmission circuit, along with remote monitoring devices to provide end users with a real-time measurement of solid contamination levels in accordance with ISO cleanliness codes. High-performance devices can identify particles down to 4µ in size, providing an early warning of wear and potential component failure, as well as an option for integral moisture sensor to detect water contamination without requiring a separate stand-alone unit.

With global demand for renewable energy on the increase, it’s essential that even aging turbines function reliably and to their full potential, while requiring as little maintenance as possible. In doing so, operators can ensure their turbines are properly meeting the need for wind power, while generating a healthy profit for business.


Matt Fielder is the industrial business development manager for the Hydraulic Filter Division, Europe, of Parker Hannifin.  

Parker Hannifin Ltd.
www.parker.com/hfde