TURBINES Today’s power generation turbines are working under more demanding conditions than ever – from continuous 24/7 running, to frequent stop-start cyclic operation to accommodate fluctuating power generation.

As a result, modern turbine oils must be able to cope with increased stress and considerable design and operational challenges, including reduced downtime, extended oil drain intervals, higher temperatures and loads. Greater turbine output power, combined with a lubricant reservoir that is the same size or smaller, is also imposing more rapid cycle times on lubricants, resulting in the need for excellent surface properties.

Looking at the ratio of turbine megawatt output to oil volume gives an indication of oil stress, and increases are being seen of up to 400% with the latest turbines. This is having a big impact on the types of lubricants required by power generation customers. Turbine oils need to help deliver value through extended oil and asset life, enhanced equipment protection and excellent system efficiency.

As turbines have developed, oil has improved. TOST (Turbine Oil Stability Test) life provides a comparative measure of how quickly different oils degrade under the same severe conditions. Twenty years ago, turbine oil might have been expected to last to around 5,000 hours, whereas today it lasts >10,000 hours. The figure below compares the oxidative stability of different oils.


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WIND TURBINES Wind power is playing an increasingly prominent role in today’s global energy mix. Industry projections suggest that existing installed capacity will double by the end of 20194


The past decade has seen vast increases in size and capacity of both on and off-shore wind turbines. Tower heights now commonly reach 80-120 m, rotor diameters average 95 m or more, and average output capacity has increased to 1.96 MW, or 3.6 MW for offshore. In addition, 27% of wind turbines installed in 2014 use direct drive technology, and this trend is growing.

All of this poses a number of challenges for lubrication. Longer turbine blades result in increasing loads and vibration on bearings, which can cause increased wear. While the high flow rate for gear oils in a wind turbine gearbox (in cases 200 L/min or more) means that the oil has little time in the sump to release any entrained air. As such, gear oils need to be designed with low foaming tendency.

With turbines often located in extreme climates, lubricants must be able to perform efficiently in spite of freezing winters, or at the other extreme, very high ambient temperatures and frequent sand storms. For turbines located off-shore or in coastal environments, protecting bearings against corrosion by sea water is also vital. At the same time, the lubricant must resist the formation of harmful deposits and retain its wear protection properties when contaminated with water. The longer an oil resists degradation, the longer the oil and machinery can keep working.


For natural gas engines, key among the challenges are the increased risk of carbon deposit build-up on the piston ring grooves and piston top land, especially in new generation high output, high Brake mean effective pressure (BMEP) gas engines, along with an increased risk of ash deposit build-up in the combustion chamber that can lead to costly unplanned downtime. Engines operating on sour gases are at risk of greater deposit build up due to siloxanes, along with corrosion as a result of halogenic compounds and acidic elements being present in the gas. The oxidation and nitration of engine oils can also significantly increase the acid stress and shorten the oil’s life.


Source: Global Wind Energy Council, Global Wind Report, Annual Market Update 2014.


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