Photo: Klüber Lubricants

Recent advances in wind-energy lubrication are aimed at supporting increased turbine efficiency. Synthetic lubricants have received considerable attention mostly due to their reputation for improved performance over conventional mineral-based oils. A few specialized lubricants with characteristics intended for particular tasks include low-temperature fluidity and long oil life. Such lubricants provide benefits for difficult to maintain wind turbine gearboxes. It is generally accepted that synthetic gear oils in several formulations offer protection from common failure modes, including micropitting and bearing wear. One formulation is intended for yaw and pitch drives. And greases are formulated to protect bearings against fretting corrosion, moisture contamination, and false brinelling at temperatures as low as -55ºF.

One idea suggests the reduction of maintenance costs by switching to a single lubricant for all bearings within the hub and nacelle. Sufficient lubrication of high and low speed bearings is achieved by combining the proper blend of base oil with selective additives. Pitch and main bearings are protected from wear related to false brinelling and boundary friction while generator bearings operate with the required film thickness and thermal stability. The lubricant is suitable for automatic lubrication systems and shows excellent performance at low temperatures.

In addition, a new product has been introduced for pitch and yaw gears (open gears) because the lubrication requirements for those gears are significantly different than the requirements for bearings. The recently introduced white, adhesive grease provides excellent protection against wear from high loads and corrosion from extreme environments. The thixotropic nature of the lubricant presents an opportunity to reduce the amount of grease needed to adequately lubricate open gears. Traditionally, open gear lubricants were challenging for automatic lubrication because the formulations contained base oil with high viscosities in combination with increased amounts of solid additives. But now, the developer offers a product which can be automatically applied at extremely low temperatures.

For gearboxes – enclosed gears – significant options are available. An oil life beyond five years for main gearboxes is easily achieved with formulations based on polyalphaolefins or polyalkylene glycol. The new technologies impart excellent behavior when exposed to moisture while enhancing the protection against wear across a wide range of temperatures, speeds, and loads.

Turbine operations in remote areas with extreme climatic conditions add to the lubrication challenge. Whether it’s to extend maintenance intervals and increase reliability with low-temperature hydraulic oils, or to protect blade bearings from fretting corrosion and false brinelling there is a wide range of lubricants from which to choose. Another lubricant manufacturer has developed a dry lube that it aims at extreme temperature applications. The dry lubricant incorporates graphite and molybdenum disulphide.

By Klüber Lubricants

The post What lubricants should be used in wind turbine gearboxes? appeared first on Windpower Engineering & Development.

• Wait until something fails, then repair it
• Replace components regardless of their condition at a set intervals
• Predict when maintenance will be needed and perform it then

Under the umbrella of condition monitoring, there are several technologies aimed at predictive maintenance. These technologies are adaptable, appropriate or relative at certain points in a wind turbine’s design life. Such technologies include but are not limited to:

• Oil analysis
• Vibration analysis
• Alignment
• Ultrasound
• Infrared thermal imaging

Combine the appropriate technology for the turbine, or the condition to be measured or predicted. The appropriate technology is the one which garners the best results for the appropriate response.

What makes condition monitoring difficult for wind is that the application is 300 ft in the air and runs at variable speeds with intermittent operation and under variable loads. The technologies listed above are meant to provide the following at a minimum:

• Measure or detect an issue
• Identify the issue
• Estimate the degradation
• Transmit that information out to appropriate parties

Most people think of condition monitoring systems (CMS) as vibration condition monitoring. Vibration condition monitoring does provide several months lead time to failures depending on the location of the assets.

Despite the great value of CMS, there are few people globally certified and experienced in vibration analysis of wind turbines. Because of this wind-industry specific shortage, there are persistent problems with its use of CMS which include short lead times for replacement components, missed calls (not recognizing the warning of impending failure), false alarms, percentage claims of efficacy, and generally a less-than-expected performance. Ironically, these issues exist only in the wind industry, not in other vertical markets that use condition monitoring.

A culture of reliability and predictive maintenance must form in the wind industry for its success. Part of this adoption is to understand who touches the system in an organization. When properly implemented, CMS can have far reaching and positive effects.

By David Clark with Bachman electronic

The post What methods of condition monitoring are available for wind turbines? appeared first on Windpower Engineering & Development.

Photo courtesy of Hydac USA

Filter elements are rated on their ability to remove contaminants of specific targeted sizes from a fluid under specific operating conditions. Filtration ratings can be measured by analyzing three areas of performance:

1. Dirt holding capacity
2. Absolute rating (micron) and percent efficiency (beta ratio)
3. Pressure drop across the element at a specific absolute efficiency

Filters with increased performance provide the benefits of longer filter change intervals, improved oil cleanliness and higher nominal flow rates. Since 2000, the dirt holding capacity of a filter element with a 10 µm(c) media has been increased by more than 100% with design improvements.

Characteristics of a Good Hydraulic Filter
Filter elements are complex hydraulic components. In addition to the three characteristics above, others play an important role. These are flow-fatigue strength, differential-pressure stability, Beta value (efficiency) stability and wide fluid compatibility. This lead to:

• The efficiency and absolute rating of a filter element. These are essential for the system’s oil cleanliness over the entire service life.
• The flow-fatigue strength of the filter material, which ensures the required oil cleanliness also with changing volume flow.
• Long filter-change intervals come from a high dirt holding capacity, and sufficient flow fatigue strength and material resistance.
• Differential-pressure stability guarantees intact and functioning filter elements especially during cold starts which stress filter materials with a low oil viscosity.
• The differences between original and replica filter elements are detectable only in a laboratory on a suitable test bench and by standardized tests.

Today’s Demands
It’s no surprise that user requirements vary. However, the trend is clearly going to higher oil cleanliness levels and longer filter change intervals as well as to an increased media resistance and compatibility with various hydraulic oils.

Special requirements call for special solutions. For example, filter elements for split power transmissions may require a high flow-fatigue strength, water absorbing elements or electrically conductive filter elements when using oil with low conductivity.

Special Problems: Electrostatic Charges
The conductivity of an oil depends on the base oil and additives. Another trend is toward higher refined base oils (group II and III) because of environmental standards. However, these oils display a lower electrical conductivity because they no longer contain heavy metals, and can generate electrostatic charges under certain operating conditions such as high fluid loading.

A non or low-conductive hydraulic oil in a system generates an electrostatic charge at the interfaces between oil and non-conductive surface, such as between the filter fleece and hoses. The charge is a result of the fast separation of two non-conductive surfaces. Thus the charge cannot be balanced thereby producing a charge separation. A large enough charge will produce discharges in the form of flashes. Because of the large non-conductive surface in the filter elements, the effect may occur and grow with increased oil flow.

Conventional filter material may be damaged due to discharge flashes and their related high temperatures. Discharges also produce holes in the filter media through which dirt particles may pass. This results in an increased wear of the hydraulic components, which can end in malfunction and machine failure.

High-temperatures flashes also lead to a deterioration of the oil characteristics, a reduction to oil life, and premature oil aging. The resulting oil-aging products also shorten the filter element life. Adjacent electric components may also be damaged by electric discharges.

A Solution To Electrostatic Charges
Static charges must be balanced to ensure that the electric discharge of the oil does not exceed certain values. For this, a filter element has been developed to ensure charge balancing and prevents the flashes.

System Solutions
The design trend towards system solution continues. With increasing importance of Supply Chain Management among machine manufacturers, there is a clear trend towards integrated solutions in the supply chain. This includes functional and system integration with particular focus on the reduction of interfaces as well as on the production of pre-assembled and tested functional units.

By Meagan Santos, Hydac USA

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