What parts of a turbine are most vulnerable to unplanned maintenance and downtime due to improper oil and grease levels?
The gearbox is critical, so having the oil analyzed as scheduled will prevent the unit from becoming inoperable. A gearbox in a wind turbine is exposed to harsher load patterns that would not traditionally be seen in a factory. In a factory, gearboxes typically turn at the same rate and carry a standard load on them. In reality, wind-turbine gearboxes are subjected to randomly changing wind speeds, which can create additional torque on the gears, thereby creating more load on the gears. Conditions from the environment also affect the oil in the gearbox, especially with large temperature changes. The viscosity of the oil will change, which will affect the operation of the gearbox and accelerate the degradation of the oil.
The second most critical component is the pitch system, so routine grease analysis is critical as well. Wind turbines must constantly adjust the pitch to get the most energy. When you see a wind turbine stuck inoperable and obviously pointed in the wrong direction, chances are this is due to a lack of proper testing and maintenance, particularly grease analysis.
What is trend-based oil and grease analysis?
By doing routine testing on a regular basis and on a set schedule, you will naturally see how the analysis is trending and changing over time. One of the challenges of operating an oil analysis program is being diligent with the schedule. When there are gaps in sampling, certain assumptions must be made as to whether the results are truly a trend or an anomaly.
If one of the parameters being monitored has increased significantly from the last sample, then one must ask: Is the asset in threat of failure, or is the result in line with what is expected? Reporting on sample schedule adherence is very beneficial and should be a part of your sampling program.
How can trend-based analysis help minimize equipment downtime, enable more efficient maintenance activities, and protect warranty claims?
Insight at a molecular level of your grease or oil is important so that you do the proper maintenance and prevent a catastrophic event to the asset.
Access to the unit is not easy, so you want to minimize trips up to the unit. So, having good data from your last sampling will prepare the engineer with the next maintenance needs.
How is an oil analysis performed on a turbine?
They are sampled very much like any other asset that contains oil or grease. For most standard analyses done, the lab needs a four-ounce sample of the oil and two ounces of grease. It is very important to obtain a representative sample. Ideally, a sample would be taken while the system is in operation, but if it must be taken offline for sampling, then the sample should be obtained within an hour of shutdown. Since wind turbines must be taken offline for an engineer to climb up for service, sampling the best process would use a vampire pump and drop tubing.
It is not recommended to sample from the drain plug as many of the wear metals and contaminations settle at this point and would not be a representative sample. Samples are obtained up tower of the unit and sent back to the lab for analysis.
Once they arrive in the lab, they are processed and analyzed on various instruments such as an inductively couple plasma spectrometer (ICP), viscometer, Fourier-transform infrared spectrometer (FTIR), particle counter, total acid number titration, ferrous wear, and Karl-Fischer titration.
How does the analysis help prevent unplanned maintenance?
By properly interpreting the lab data received by a trained professional, the engineers can then make informed decisions on maintenance plans or schedule a future sample analysis. This data helps shift from a reactive mode to a preventative/predictive mode, affecting the number of unplanned outages.
What kinds of information can an oil analysis reveal?
Wear, particle contamination, additive levels, and overall lubricant condition can be revealed by oil analysis. Viscosity measured at 40oC according to ASTM D445 is one of the most important tests since viscosity has such an impact on the temperature of the gearbox. If the viscosity is too high, then the gearbox will run hotter, which will decrease the life of the lubricant. ICP according to ASTM Method D5185 will monitor the amount of additives, contaminant, and wear metals smaller than seven microns, giving insight into machine and lubricant condition. FTIR ASTM Method E2412 is used to monitor degradation products, additives, and contaminants. Total Acid Number ASTM D974 is done via titration, and results provide indications on lubricant health.
As a lubricant’s antioxidants are consumed, acids are not neutralized, causing increased acidity, which is detrimental to fluid health and ultimately affects internal components within the asset. Particle Count ISO Method 4406, which uses the pore block method and indicates how much contamination is in the oil and what particle size are the contaminants. If particulate levels are not monitored and left to increase, it can lead to accelerated machine wear. Ferrous wear measures larger particles of iron wear in the sample, which would not have been seen via the ICP analysis due to its larger size. Karl-Fischer titration ASTM Method D6304 is a titration that quantifies the amount of water that is present in the sample.
Karl-Fischer would be used only if a Crackle Test were positive, which only indicates that water is present, which is only a qualitative measurement.
How often should an oil analysis be performed?
Traditionally, when looking at assets for how often to sample, we look at three questions. 1) Is the asset critical to operation? 2) How often does it run? and 3) Do you have spare? Wind turbines are different because of access difficulty, and in essence, all assets are critical to operation. Industry standards suggest sampling at least once per year but no more than twice a year unless there is an issue with the unit. Again, with the limited opportunities to pull the turbine samples, it is imperative representative samples be taken. Additionally, it is important the technicians are properly trained in sampling best practices.
Once an analysis report is prepared, what are the next steps for maximum turbine efficiency?
Traditional maintenance of the unit and adjusting any red flags received from the lab analysis according to OEM recommendations are the next logical steps. Engineers should be trained in interpreting the results of the oil analysis reports so that action can be taken. Training classes that would prepare technicians for certifications by STLE or ICML are readily available and should be used. 
More info testoil.com
