How to take oil samples properly?
In this short blog post we share a basic guideline and set of recommendations how to take oil samples properly.
Introduction
Analyzing the quality of transformer insulation oil by means of oil samples is a standard practice used for decades. Important is to keep in mind that it is not just about “filling the bottle”. The way how the samples were taken has a crucial impact on the results of the oil analysis. Following several simple steps make sure that you get meaningful results of the oil analysis.
When to take oil samples?
Before sharing the recommendations how to take oil samples properly it shall be explained when the samples are actually taken.
Oil samples are taken as part of routine testing, i.e. the procedure applies to each and every liquid immersed transformer. Moreover, as part of type testing oil samples are taken before and after the temperature rise test. Finally, it is a good practice to take oil samples in regular intervals during the service life of the transformer and observe the trend.
Procedure how to take oil samples properly
– Oil samples are taken exclusively in closable glass vessels. Those vessels had been washed out and dried out beforehand followin the internal regulations.
– Dedicated sampling valve(s) shall be used for oil sampling. Larger transformers may have multiple sampling valves.
– Samples must not be taken while raining or presence of fog or snow or when the relative humidity exceeds 70%.
– Before taking a sample approx. 5 l of oil shall be drained out. The equipment for sampling and the vessel shall be flushed by the oil.
– Sampling time shall be as short as possible minimizing the contact of oil with the atmospheric environment.
– Oil contamination during the sampling process must be prevented.
– After filling the vessel shall be immediatelly closed. The samples shall be kept out of direct sunshine. Unnecessary temperature changes shall be eliminated. The samples shall be delivered to the laboratory as soon as possible.
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References
[1] Diagnostic and maintenance of electric machines, Prague 1984
[2] VFD transformers – All articles, https://mb-drive-services.com/category/vfd_transformers/
Capital spare transformer – A valuable asset (article here)
