For Wind Turbine Operators, Choosing the Right Lubricants Can Make a Big Difference

 23rd Jul 2012

Q1: How extensive is ExxonMobil’s portfolio of lubricants for wind turbines?

 Hawkins: ExxonMobil has been pioneering synthetic lubricant technologies for nearly half a century and has a long-standing reputation for serving even the most demanding applications including wind turbines.

Today, we have an extensive portfolio of expertly formulated lubricants that deliver exceptional, long lasting performance for wind turbine operations.

Perhaps the most recognised product is our flagship Mobilgear SHC XMP 320, a high-performance synthetic gear oil for wind turbine gearboxes. Mobilgear SHC XMP 320 is used in more than 30,000 wind turbines worldwide and is the initial-fill gear oil of choice for the majority of the world’s top 12 wind-turbine builders.

The proven performance of Mobilgear SHC XMP 320 was recently demonstrated in a series of wind turbines manufactured by REpower Systems AG operating at the Thornton Bank offshore wind farm in Belgium. REpower Systems carried out research which revealed the availability of the six REpower 5M turbines in the Thornton Bank wind farm has been consistently above 97 percent over a period of six months. The use of a high performance gear oil contributes to improved reliability in a turbine and since the turbines were officially commissioned more than 4,000 full load hours have been recorded, despite adverse conditions in the open seas.

At ExxonMobil, we recently analysed more than 15,000 used-oil samples of Mobilgear SHC XMP 320. The results demonstrated that the oil delivered superb wear protection with few issues related to ageing detected during the analysis.

As well as Mobilgear SHC XMP 320, we offer a wide range of lubricants that are formulated to deliver exceptional protection for all parts of a wind turbine, including greases to lubricate bearings and hydraulic oils that help pitch rotor blades.

Mobil SHC Grease 460WT is our premier synthetic grease for the lubrication of main, pitch and yaw bearings and offers exceptional low and high temperature performance, structural stability, even in the presence of water, false brinelling protection, excellent wear protection and rust and corrosion inhibition. It allows consolidation of main, pitch and yaw bearing greases into one product, reducing the risk of re-lubrication with the wrong product and without introducing unnecessary operational risks.

In addition, our Mobil SHC 524 high performance synthetic hydraulic oil delivers exceptional performance in critical wind turbine applications, such as the pitch control of rotor blades.


Q2: Why is lubrication such an essential component of wind turbine performance?

Hawkins: Wind turbine maintenance presents many challenges that can impact productivity.

The main gearbox drives the generator and is the heart of a wind turbine. With their advanced designs and overall importance to system performance, gearboxes can be very costly to repair or replace after the warranty expires. For example, when factoring in all expenses, replacing a gearbox for a 1.4 MW turbine can cost a company more than €400,000, including the price of a new gearbox, labour costs, crane rental and lost revenue from turbine downtime. In remote locations like offshore, costs might be even higher and after the warranty period, the operator becomes responsible for keeping the turbine running for the remainder of its service life.

For the main gearbox, as for all pieces of industrial equipment, lubrication plays a vital role in optimising performance and minimising downtime.

As the lifeblood of the equipment, lubrication mitigates friction between components of the main gearbox. Considering that the average wind turbine is designed to operate for up to 20 years and the potential challenges and costs associated with maintaining a wind turbine gearbox, it is recommended that maintenance professionals use a well-balanced synthetic gearbox lubricant, like our Mobilgear SHC XMP 320.


Q3: What are the key challenges facing wind turbine operators and maintenance personnel?

Hawkins: Maintaining and prolonging the performance of the main gearbox is the greatest lubrication challenge in a wind turbine. The most common cause of gearbox downtime is related to bearing failure.

Considering the variable load, speed and dramatic temperature conditions wind turbines operate under, bearings are put under a significant amount of stress. These factors, combined with improper lubrication, can result in the need for bearing replacements, and if damaged bearings are not replaced promptly, significant gear damage can result.

The drive to minimise up-tower weight has resulted in compact gearbox designs which, in combination with high loads found in wind turbines with hardened surfaces, makes these gears susceptible to micropitting, which can cause numerous surface cracks. The cracks propagate at a shallow incline to the surface, forming extremely small micropits that can reduce gear tooth accuracy and lead to significant gear damage.

In addition to protecting against micropitting and other forms of equipment wear, Mobilgear SHC XMP 320 exceeds the performance of traditional oils by extending the interval between oil changes from 18 months to three years or more.Extended oil life translates into a variety of benefits, including reduced volume of oil purchases, used-oil disposal volumes, maintenance effort and lubricant-related downtime for oil changes.


Q4: Why does using synthetic lubricants vs. conventional oils make such a difference in wind turbine applications?

Hawkins: The need for manufacturers to minimise up-tower weight in wind turbines has resulted in compact gearbox designs that incorporate the case hardening of the gear surfaces. Case-hardened gears exposed to unpredictable winds and loads found in wind turbines are susceptible to micropitting and require a gear lubricant that protects against this type of wear.

The extreme conditions wind turbines are subjected to are easily endured by high-performance synthetic lubricants. By comparison, conventional, mineral-based fluids really cannot deliver the same level of protection. Upgrading to synthetic lubricants brings a number of advantages which help maximise the performance of wind turbines.

Compared to conventional mineral oils, Mobil SHC fluids can actually reduce energy consumption in many applications. Other advantages include longer equipment life, high-temperature capability, excellent resistance to oxidation and protection against wear. These kind of performance advantages can help our customers to generate significant bottom line savings and, equally important, enable them to maximise their productivity.


Q5: How different a challenge is it to lubricate wind turbines located onshore vs. those in offshore conditions?

Hawkins: There are some differences in conducting oil changes with wind turbines that are offshore versus onshore. Offshore, wind turbines may be as high as 300 feet or more and there are potential rough seas to contend with and, of course, strong winds. Typically, the main gearbox is located right in the centre of these extreme conditions.

Also, change-outs for hydraulic systems are more costly and challenging in offshore applications. So the benefits of choosing synthetic lubricants versus conventional, mineral-based oils are even more pronounced in offshore environments.

At ExxonMobil, we are committed to building on the success we have achieved in on-shore markets to date and extending that success to off-shore installations. We have some really exciting innovations in the pipeline.


Q6: Besides choosing the right lubricant, what other maintenance strategies are essential for maximising wind turbine performance?

Hawkins: Oil analysis is one of the most widely used proactive maintenance strategies for wind turbines and employs a test slate that is designed to evaluate the condition of the in-service lubricant and the condition of internal hardware. Using routine oil analysis as part of a preventative maintenance programme, maintenance professionals can extend the useful lives of both the gear oil and the gearbox by detecting and acting on early warning signs, such as contamination or increasing wear metals.

To obtain the greatest benefit from oil analysis, it is imperative to work closely with an expert lubricant manufacturer and participate in oil analysis every three to six months. Identifying trends in the data will help maintenance professionals make better informed oil suitability decisions.

Q7: Describe the importance of ExxonMobil’s partnerships with wind turbine and gearbox manufacturers?

 Hawkins: Over the years, original equipment manufacturers (OEMs) have focused on developing new, more compact and efficient equipment that is capable of delivering even higher load capacities.

The upside is that these newer units, often with smaller footprints, frequently provide better overall performance than their predecessors. The downside is that such improvements sometimes put additional stress on lubricants in terms of higher operating temperatures and load conditions. These effects are compounded by the OEMs’ drive to reduce total life cycle costs for their products. This includes reducing oil volume while extending oil drain and re-greasing intervals.

A key factor in the development of lubricants is the close working relationships that our ExxonMobil scientists and application specialists have with key OEMs. Through these technology partnerships, we are able to ensure that our product offerings deliver exceptional performance and are ideally formulated to meet the rapidly evolving gear designs and operation requirements.



Notes For Editors

Article source:
Author: Kari Williamson

The WP Group, headquartered near Southampton in Hampshire, is a leading independent distributor of fuels and lubricants, with a £160m annual turnover and employing 70 people.

Based at Wessex House, Cadland Road, Hardley, Hythe, WP offers a complete portfolio of products and bespoke service solutions across each of its eight trading divisions - ­ Industrial, Aviation, Agricultural, Heating, Automotive, Commercial, Motorsport and Marine.

WP, located by Fawley Oil Refinery, has a 50-year heritage and is the supplier and support specialist of choice to thousands of businesses.

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