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Analysing what lubricants should be used in wind turbine gearboxes

India’s power sector is one of the most diversified in the world. Sources of power generation range from conventional sources such as coal, lignite, natural gas, oil, hydro and nuclear power to viable non-conventional sources such as wind, solar, and agricultural and domestic waste. Electricity demand in the country has increased rapidly and is expected to rise further in the years to come. To meet the increasing demand for electricity in the country, massive addition to the installed generating capacity is required.

Lubricant technology plays a vital role in keeping wind turbines running reliably and efficiently. The OEMs and customers today are constantly striving to improve efficiency and operational reliability, and enhance competitiveness by avoiding loss of output and increased maintenance costs. Besides reducing friction and offering strong reliability to equipment, lubricants also play a vital role in terms of energy efficiency

The wind industry has traditionally believed that value creation is concentrated in manufacturing and wind farm development. One of the most important aspects of a wind turbine is the reliability of its ‘critical’ components (gearbox, generator, blades etc.). These parts need to be properly conserved and maintained to achieve an optimum level of performance and reduced need for costly maintenance. Typically, in wind turbines, large components’ failures such as those of gearboxes, main bearings, etc. take about eight to ten weeks or even longer to repair or replace. Especially in today’s scenario of high demand, component lead time represents more than 80 to 90 per cent of total downtime.

While sharing his views on what lubricants should be used in wind turbine gearboxes Siva Kasturi, Asia Pacific Regional OEM Manager, Shell Global Lubricants says, “When talking about lubrication in the wind energy sphere, one need to focus on increasing turbine efficiency. To maintain wind turbine gearboxes and to avoid equipment downtime, the lubricants should be broadly characterised with low-temperature fluidity and long oil life under continuous operating conditions. Moreover, products should be designed to have exceptional oxidative stability and resist water contamination effects.”

In today’s world, cold climates and offshore applications expose the turbine gear to difficult conditions, and hence generate a greater need for the use of proper lubricants.

Shell has developed a lubrication plan and tailored its products and services to optimize the efficiency of wind farms. He adds, “One of our key products, Shell Omala S5 Wind 320 is the most advanced next generation synthetic wind turbine gear oil which offers exceptional component protection and lubrication even under the most severe operating conditions. This high-performance lubricant will protect wind turbine gears and bearings by minimising wear, protecting against micro-pitting, maintaining fluidity at extremes of temperature and controlling foam even when used in conjunction with fine filtration.”

Shell is proactively working with OEMs about introduction of new technology Gear oils (i.e. Omala S5 Wind 320) considering the revised IEC 61400-4 specifications. Shell also offers the most comprehensive range of high performance synthetic greases for wind turbine applications (Gadus S5 V 460 KP 1.5 and Gadus S5 V 110 KP) for main bearings, Yaw and pitch bearings.

“As a leading player of the lubricants market, we are committed towards providing offerings that are high on value. We also host and participate in a multitude of knowledge-sharing events and discussion forums,” says Kasturi.

New advances in wind-energy lubrication support increased turbine efficiency. Synthetic lubricants receive considerable attention mostly due to their reputation for improved performance over conventional mineral-based oils. It is generally accepted that synthetic gear oils in several formulations offer protection from common failure modes, including micropitting and bearing wear. While, one formulation protects the yaw and pitch drives, greases are formulated to protect bearings against fretting corrosion, moisture contamination, and false brinelling at temperatures even as low as -55ºF, informs Rajeev Sharma, Vice President O&M, Asset Management, Mytrah Energy India Ltd.

At the same time, there are few specialised lubricants that alleviate specific issues such as low-temperature fluidity and longer oil life. These lubricants are really helpful when it comes to easy maintenance of wind turbine gearboxes. He adds, “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. Such lubricants are suitable for automatic lubrication systems and shows excellent performance at low temperatures too.”

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. “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 the open gears,” says Sharma.

Dr Sanjiv Kawishwar, Sr. Vice President, ReGen Powertech shares few points on lubricants that should be used for wind turbine gearboxes:

• Lubrication in wind turbine gearboxes play major role to determine turbine efficiency.
• Synthetic lubricants are used in gearboxes.
• Mineral-based oils are now replaced by Synthetic lubricants in order to achieve enhanced performance.
• Specialised lubricants with low-temperature fluidity and long oil life are preferred by designer to ensure ease of maintenance.
• Studies reveal that synthetic gear oils that provide protection from failures like micro-pitting and bearing wear are preferred over traditional lubricants.
• Bearings are protected against fretting corrosion, moisture contamination and false brine ling at lower temperatures (as low as -55ºF) by using rightly formulated greases to protect bearings.
• Reduction of maintenance costs are achieved by developing single lubricant for all bearings within a wind turbine.