Research has shown that elemental and optical particle counting tests performed on oil samples do not provide clear insight on gearbox health. But why?


When relying on wear debris data to make important decisions about maintenance of wind turbine gearboxes, it is important to ensure that this oil samples are providing an accurate representation of the amount of debris being generated. If a gearbox is faulty and it is generating wear debris, you would expect it to be represented in oil samples. However, data has shown that this is not the case. If the debris is not ending up in the sample then, where is it going? There are three main reasons oil debris is not captured in samples taken:

1. Oil Filtration Systems

One clear answer for where the debris is going is simple: it has been filtered out. Filtration systems generally remove particles larger than 5-50µm. Therefore, most of the wear debris that is useful to show gearbox health is filtered out before the sample is taken and analyzed.

2. Small Sample Size

Even if the sample is taken before filtering, it is extremely unlikely that a representative sample of debris is captured in a 4-ounce sample beaker. The average particle-size distribution of a wear debris particles from a typical fleet of wind turbines, and online monitoring found that the concentration of even the most abundant particles (100–200µm) were only found once in every 20 liters of oil. Given the typical 4-ounce fluid sample, this means that there is roughly a .6% chance that the sample finds any debris in the sample.

3. Irregularity of Generation

Another main issue is that generation of metallic wear debris is that it is not a continuous or predictable process. Generation rates are drastically different depending on how developed the fault is and operating conditions such as temperature and wind speed. At any point in time, any number of gearbox conditions can lead to wear debris being released, getting stuck, or settling making it nearly impossible to collect a sample that shows the true health of the asset at any given point.

Given the factors above, a small sample taken at a single point of a very complex system that can impact the amount of metallic debris in oil at any given time is not going to provide accurate nor reliable results that have the ability to identify faults or make any number of other important decisions based on gearbox health. Some samples may display levels of debris data that trigger warning or alarm alerts, while others are likely to show nothing significant at all—even when a fault is in fact present.

Online oil health monitoring is able to mitigate some of these risks and provide far more reliable data regarding the actual health of an asset at any given time. Poseidon Systems’ Trident DM sensors utilize real-time, condition based monitoring to provide more accurate data on debris generation over a period of time.

To learn more about the limitations of offline oil analysis, download our whitepaper, co-authored by EDF Renewables, here!