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Advertorial: “Lubricants can make a big difference”

Renewable Energy Focus

FOR WIND turbine operators, choosing the right lubricants can make a big difference. Michael Hawkins, global brand manager for ExxonMobil's Mobil SHC brand of synthetic lubricants details how ExxonMobil's flagship lubricants and application expertise is helping the wind energy sector to expand and become more cost competitive.

How extensive is ExxonMobil's portfolio of lubricants for wind turbines?

Michael Hawkins (MH): 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 manufacturers.

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. Mobil SHC Grease 460WT is our premier synthetic grease for the lubrication of main, pitch and yaw bearings and 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.

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

MH: Wind turbine maintenance presents many challenges that can impact on 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.

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

MH: 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 micro-pitting, which can cause numerous surface cracks. The cracks propagate at a shallow incline to the surface, forming extremely small micro pits that can reduce gear tooth accuracy and lead to significant gear damage.

In addition to protecting against micro-pitting 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.

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

MH: 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 micro-pitting, 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.

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

MH: 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 6 months. Identifying trends in the data will help maintenance professionals make better informed oil suitability decisions.

Describe the importance of ExxonMobil's partnerships with wind turbine and gearbox manufacturers?

MH: 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.

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Renewable Energy Focus, May/June 2011.

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