Wind turbine lubricant sampling, flushing, and analysis

1© 2014 Maintenance Reliability Group, LLC. All rights reserved.

Wind Turbine Lubricant Monitoring

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Strategies for Wind Lubricant Sampling and Analysis

• Experience with additive sludging in gearbox applications

• Flushing strategies for wind gearbox for lubricant changeover

• Retrofit for improved gearbox sampling options

• Drivetrain grease sampling

– Main Bearings

– Pitch Bearings

– Generator and Yaw

• Danish wind industry research results

• Grease Analysis

• Case Studies


Variable moisture levels in traditional gearbox oil


Moisture in Gearbox oil


Moisture in Gearbox oil


Gearbox oil particulate-conclusions

• Sulfur is an element found commonly in EP additives, and seen in this concentrations it is unlikely to be from an environmental source.

• The additive package from the lubricant product used in these gearboxes is contributing to the formation of small crystal particles during exposure to the real operating conditions seen in this application, including varying water concentrations.

• Consider reevaluating the lubricant choice for this application or improving control of the water concentration, which may affect the stability of the additives in the current product.


Flushing gearbox oil for changeover

• Location of gearbox uptower makes flushing difficult

• Importance of minimizing oil carryover during new product changeover

• Specialized equipment and processes for maximum flushing effectiveness.

Image from http://www.sageoilvac.com/


Proper Flushing

• Use of flushing agent

• Heating of oil to lower viscosity and improve flush

• Removal of access covers and use of extensions to direct flow and suction

• Flushing and jetting planetary and other sections

• Sampling and analysis to confirm flushing effectiveness


Sampling Fitting installation

• Angle of gearbox may require different placement of sampling fitting

• Retrofit of drain with pitot tube to avoid “crud trap”

• Multiple samples to address main & planet gear sections

Image from http://www.nrel.gov/

10© 2014 Maintenance Reliability Group, LLC. All rights reserved.10

Grease Sampling Grease Sampling ToolsTools


MOV Gearbox

1 2 3 4 5

Electric Motor Bearing

1 2 3 4 5

Pillow Block Bearing1 2 3 4

Sampling TechniquesSampling Techniques


Main Bearing Sampling

• Grease flow dependent on temperature, bearing movement

• Grease Thief & T-handle used to capture flowing grease

• Revised T-handle developed for Denmark Off-shore Wind Research Project

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Other Sampling Locations

• Pitch bearing grease bellows

• Can be removed and sampled in lab

• Grease Thief or spatula used to sample drain path behind bellows trap

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Other Sample Locations

• Generator bearings for install of Grease Thief

• Use of T-handle to position for sample in active zone

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Types of Grease Analysis

• Performance

– Tribological, oxidation resistance, etc.

• Quality Control

– Batch conformation, Penetration value

• Failure Analysis

• In-service testing

– Equipment wear condition

– Contamination of grease

– Consistency changes

– Oxidation condition

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Analysis Techniques

Sample is received. fdM+ is run Die extrusion is performed and substrate is made

Two strips are used to make a dilution to run RDE/ICP.

One Strip is used for FT-IR.

One Strip is Dissolved in Green RULER solution to run RULER.

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Grease Thief Analyzer To Measure Consistency with 1 Gram


Grease Thief Die Extrusion and Anti-Oxidant Testing


Die extrusion and sample preparation

•Extrusion of the grease at varying rates

•Load cell response used to measure flow and shear characteristics of grease

•Compared to new fresh grease

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Grease Consistency – Back Bearings in a USA Wind Farm: Outliers in Yellow


Grease Consistency – Front Bearings in a USA Wind Farm: Outliers in Yellow


Linear Sweep Voltammetry and FTIR

•RULER test establishes anti-oxidant levels in new grease

•Purged grease levels show residual anti-oxidants; can be used to adjust greasing frequencies, indicate abnormal oxidation stressors

•FTIR can show oxidation, presence of grease thickener type, organic contaminants

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Optical Spectroscopy

•Optical spectroscopy quantifies the appearance of grease

•Grease aging, contaminants, mixtures, chemometrics

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The 100x ferrogram is seen in white reflected and green transmitted light, to show normal presentation of entry deposit particulate.

The 100x ferrogram is taken in crossed polarized light. Resulting illuminated particles are crystalline debris, typically indicative or dirt or other abrasive contaminants.

Analytical FerrographyAnalytical Ferrography


Wear Levels Across a Fleet of Wind Turbines-USA

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Wind Turbine grease sampling and analysis

• 2-year project conducted with DONG Energy and Vattenfall, two largest offshore wind operators in the world

• Dr. Kim Esbensen, internationally recognized expert in Theory of Sampling (TOS), Denmark

• Rich Wurzbach, MRG Labs, inventor of Grease Thief

• Systematic evaluation of grease heterogeneity, sampling methodology, and analysis validity and repeatability for wind turbine main bearings in on-shore and off-shore applications

• Results published at OilDoc, LUBMAT, and AWEA


• Fundamental Sampling Principle

–Using the Grease Thief

• Representative sampling

–Thorough characterization of the heterogeneity of grease in main bearings


Test parameters of Grease

• For the heterogeneity characterization of grease in main bearings of wind turbines the following parameters were used:

–Consistency and flow characteristics

–Ferromagnetic iron (Hall-effect sensor)

–Wear metals

–Particle characterization (size & distribution)

–Residual oil in grease

–Antioxidants


Heterogeneity characterization – Ferromagnetic iron

• Sampling of grease while draining the main bearing through the drain plug

• 27 increments collected (each sample approximately 20 grams)

On site sampling

10000

12000

14000

16000

18000

20000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Sample no

Iron

(FdM

Plu

s)


3D-sampling, OEM repair shop


3-D Sampling, OEM repair shop


3-D sampling


• Analysis of iron (Fe) using a analytical method which only detects particles < 6 µm

• Note, this method gives iron concentration from 50 to 170 ppm

› Analysis of ALL ferrous magnetic particles irrespective of size (Hall-technique).

› Note, this method gives iron concentration from 30.000 to 40.000 ppm

Ferrous debris method comparison


Comparison of ferrous levels from different sampling procedures

“SWP” is Siemens Work Practice: standard method for grease sampling of disassembled bearing in the shop


Comparison of grease consistency (by Grease Thief Index) of different sampling procedures


Conclusions from 3-D samplingOEM repair shop

• Analysis of analytical results reveal no statistically significant differences between the 3D sample arrays extracted

• The grease is thoroughly well mixed

• Standard SWP bearing samples falls fully within the span of the 3D experimental results. This also apply to samples taken close to inspection cover

• It is concluded that standard bearing sampling (for the bearing investigated) results in valid characterization of the grease.


Phase 2 – Field trials

• Grease analysis parameter

–Iron using a ferro-magnetic debris Monitor (fdM, "Hall-monitor"). Measures all ferro-magnetic debris/particles in the grease irrespective of size

–Iron (and other wear elements) using Rotating Disc Electrode Atomic Emission Spectrometry (RDE). This method only detects particle < 6-8 µm.

–Characterization of wear particles using optical microscopy

–Moisture

–Consistency

–Anti-oxidants using RULER-technique


Trends for fdM-Fe, main bearings


Trends of moisture in wind turbine bearings

Grease type: Klüberplex BEM 41 141•Thickener: complex Li•Base oil: Mineral oil & PAO•Viscosity @ 40C: 130 cSt•NLGI-class: 2


Trends of moisture in bearings

Grease type: SKF LGWM1•Thickener: Li•Base oil: Mineral oil•Viscosity @ 40C: 200 cSt•NLGI-class: 1


Linear Sweep Voltammetry and FTIR

•RULER test establishes anti-oxidant levels in new grease

•Purged grease levels show residual anti-oxidants; can be used to adjust greasing frequencies, indicate abnormal oxidation stressors

•FTIR can show oxidation, presence of grease thickener type, organic contaminants

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Other projects: US Wind turbinesWear Levels in Comparison

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Wear levels in Robot fleet-comparison


Conclusions

• Grease in the area accessed by the Grease Thief is thoroughly well mixed and comparable to the samples taken in the shop between the rollers

• Bearings removed from service following field sampling and analysis trials corresponded precisely to the predicted condition when disassembled and characterized

• In-service grease analysis complements condition monitoring systems (vibration analysis) and is particularly useful in slow-speed shafts where some vibration trends lag grease condition and wear particle indications

• Grease sampling can be cost-effectively deployed during periodic uptower maintenance visits with easily understood and utilized sampling kits and tools

• Early detection of abnormal conditions can be sometimes rectified uptower (grease flushing, relubrication, etc) substantially reducing the event cost and risk of failure

Engineering

Wind turbine lubricant sampling, flushing, and analysis