Transformer oil sampling – Study & Analysis

Here we are writing an article to inform and to make aware our readers about transformer oil sampling. The oil in a transformer conducts both as coolant and insulation for the internal part. In doing this it scrubs almost every internal part. As a result, the oil consists around 70% of the accessible indicative information for the transformer. The claiming is to access this information and analyze it protectively to provide an early implication of a progressive condition such as tap changer arcing.

Obtaining an ideal sample

The generated data from oil sample is as good as the sample itself. A careless drawn or sample consist of impurities can nullify the test results. At ABB we have recently enhanced our sampling method to use the TFSS (Turbulent Flush Sampling System). This bunched, self-contaminated system offers different benefits consisting:

  • Promoting turbulent flush
  • Determining flush volumes
  • Producing an illustrative sample
  • Preventing sample contamination

TFSS assure that the sample is an illustration of the oil inside the transformer, rather than any impurities that might have settled into the valve.

Read more: Transformer oil Specification – Study analysis

Transformer condition assessment (TCA)

Conventional oil testing program uses only a few indicative parameters, leaving a big amount of potential oil based information investigated. Yet many surveys of failed transformer reveal many failures that can be associated with problems that could have been properly managed with an early indicative through more detailed analyzes of the indicative fluid.
ABB link this gap by working with a popular test laboratory to provide TGA (transformer condition assessment).  TCA offers a comprehensive assessment of the dielectric and mechanical state of the transformer including:

  • Dissolved gas analysis
  • Insulating fluid quality analyses
  • Particle analyzer
  • Furan analyzes

Read more: Knowledge Base: Transformer oil / Insulating Oil

DGA – a view of operational condition

Hydrocarbon oils are generally used as isolating fluids in high voltage power device such as transformers because of their one of the best dielectric strength and chemical stability. Normal degeneration of the oil is usually occurring because of oxidation. This is commonly a time consuming process. However, under the effect of an electrical fault, the oil can decompose to form a variety of low molecular weight gases that dissolve in the oil such as methane, ethane, acetylene, hydrogen, carbon monoxide and carbon dioxide.
The combination of the breakdown gases depends on the type of fault, while the quantity depends on its duration. Hence by dissolved gas analysis, it is possible to segment such transformer fault procedure as partial discharge overheating and arcing.
Dissolved gas analysis follows two steps: eradication and chromatographically analysis.
In the first step, the gases are evoked out by submitting the oil sample to high void. The volume of the evoked gases is calculated and a part of the gas is transmitted to a gas chromatograph.
The strong sensibility of the chromatographic method enables less detection limits for each gas- at the parts per million level. The noticeable sensibility and preciseness of this method ensure a huge measure of dependability for the indicative interpretation do dissolve gas analysis data.
Depending on the dissolved gases in the transformer oil it is easily possible to evaluate faults such as corona, sparking, overheating and arching.
There are several tests on the insulating fluid that offers a useful indication of how we, the transformer is being cared in services. We have a number of several tests that is mandatory to conduct including PCBs, moisture, acidity and dielectric strength.

PCB content

Though it is not related directly to the transformer performance, it is still essential to identify the presence of the chemicals known as Polychlorinated Biphenyls (PCBs) in the insulating fluid. PCBs were very famous in the late 1950s/early 1960s as an alternative to mineral oil thanks to their strong excellent insulating properties. They are highly toxic and have been banned for many years. PCBs were in service for so long to cause impurities with mineral oil stocks and it is comparatively common to identify some background records in older transformers. At levels above 50 to 500 ppm the transformer needs to be taken out of service and when possible so that it can be flushed and refilled with fresh oil.


Increase in the oil, moisture content can reduce its insulating traits and result in dielectric breakdown. This is very essential when a transformer is subjected to fluctuating temperatures, maybe when in discontinuous operation, as the cooling down process of solution can create dissolved water to come out of solution, reducing the insulating traits.


Raised acidity not only creates an environment to attack the many copper components in the transformer as well as decompose the steel tanking, it also reduces the paper insulation. Moreover, acid can also cause the formation of grease that blocks ducts and cooling galleys, results in less efficient cooling. Note, the oil must be replaced when the acidity reaches above 0.5mg/g KOH.

Particle analysis

The major approach in expressing out a higher level of indicative information from transformer has come from the identification of suspended and sediment particles found in the oil. In addition, when DGA analysis shows the presence of a possible fault, particle analysis will provide certification and pinpoint its location.

Furan analysis – a view of remaining life

Generally, the life of a well-maintained transformer with no serious operating defects will be determined by the quality of its insulating paper. When the paper disgrace it produces the organic compound known as Furans. There exist a direct relationship between an amount of furan and the strength of the paper insulation. Therefore, furan analysis can provide useful information on the transformer’s remaining service life. 


Transformer oil sampling becomes most useful task when carried out on a regular basis. Therefore it is so useful to take a benchmark sample when a transformer has been energized or an oil treatment performed and then to take further samples at regular intervals so any fault could be easily identified.
Hope you find this article helpful. To know more information visit us Powerlink Oil Refinery LtdIf you are interested in knowing about Transformer Oil Market View, you can read it here. Thanks for visiting!

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