diagnostician and practitioner, working at the Ecol Oil Analysis Laboratory, responsible for the interpretation of test results and customer support in the area of lubricant analysis.
We continue our considerations regarding the determination of limit limits for lubricating oil analysis. The last two publications discuss statistical tools helpful in determining alarm limits. In this article, the analysis of trend changes in relation to the set limits will be discussed.
Stable trends over time, even when the values exceed the limit, confirm that the gearbox is working properly from a lubrication point of view. On the other hand, the rapid increase in the content of wear metals indicates potential problems and the possibility of failure, even if the theoretical limits have not been exceeded.
An example of the iron content trends for several main gearboxes in wind turbines is presented below.
Rys. 1. Iron content change.
As we can see, the graphical presentation of trends, besides statistical limits, also makes it very easy to make a decisions about further service operations. A sudden change of the trend line clearly informs about the need to check the cause of a possible problem. Based on the service history and the observation of change trends, the following conclusions can be drawn for individual turbines:
- in the case of the “A” turbine, the visible increase in the iron content indicates that the inspection of the gear is recommended and the interval between further analysis should be shortened,
- for turbine “B”, the stable trend of iron content indicates no potential wear problems in the system,
- for the “C” turbine, after a sudden increase in iron content, the oil was changed and the situation is significantly better,
- for the “D” turbine, we initially observe a gradual increase in iron content, then, after exceeding the warning limit, the trend stabilized, but in the last analysis we can already see a significant increase. Such situation will require taking a more decisive service action and most likely changing the oil.
Summing up, the statistical analysis and the graphical presentation of the results of oil analyzes are very helpful tools when assessing the technical condition of machines. Based on the precise data obtained from the analyzes, the operators are able to maximize the production potential of the machine park and plan in advance any required service activities. Regular lubricant monitoring is an excellent tool that provides a rich information on the technical condition of machines.
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