Transformer Oil Sampling Analysis

27th October 2025

Regular oil sampling is essentially a ‘blood’ test for your asset, giving insight into its health, where the accuracy of the results relies heavily on the quality of how the sample is obtained. At EME Power Systems, we ensure all craft staff are fully trained in up-to-date practices and methods using the appropriate equipment. We pride ourselves on taking only high-quality samples.

Being non-intrusive, so non-disruptive there are various reasons you would want to include this in any PPM schedule, for instance:

  • Compliance
  • Safety assurance
  • Early fault indication
  • Managing / extending asset life expectancy

Initial Testing / PCBs

Whenever undertaking an initial sample, we will always test for PCBs. Polychlorinated Biphenyls were used in transformer oil due to their excellent electrical and thermal properties. Banned many years ago due to their toxicity and risks to health, there is still a risk of their presence.

From the 31st December 2025, a legislative revision requires their removal – please see https://www.emepowersystems.co.uk/news/pcb-regulations-changing for further information.

Ongoing testing / key health indicators:

Regular sampling analysis usually entails two main standard tests:

DGA (Dissolved Gas Analysis) – This test is one of the most revealing for transformer health, as it measures the concentrations of gases present, including hydrogen, methane, ethane, ethylene, acetylene, carbon monoxide, carbon dioxide, oxygen, and nitrogen. An increase in certain gas concentrations can signify specific internal faults. For example, a high acetylene reading accompanied by elevated hydrogen typically indicates an electrical arcing fault inside the transformer. In summary, DGA will identify faults & thermal stresses, including Partial Discharge, Overheating or Arcing.

Routine (Fluid Quality) – In addition to DGA, a routine oil-quality check is performed to monitor the overall health of the insulating fluid. Here, we check for Acidity, Breakdown Voltage, Water Content, Colour, Appearance, and Fibres. Ageing oil naturally degrades – acidity tends to increase, moisture builds up, and insulating performance drops – which can accelerate the transformer’s overall deterioration if left unaddressed.

A failure of one or a combination of these test results could lead to a critical, costly, unplanned power outage that could have been planned, managed, and rectified when identified early as part of our analysis.

Additional testing

Furfuraldehyde (Solid/Paper Insulation) - Also known as Furan’s testing, this test shows the approximate mechanical strength of the paper insulation, as indicated by the estimated degree of polymerisation. This is the measurement of cellulose insulation (estimated DP). When a transformer is new, the estimated DP is typically 1000, and when this value reaches 200, it is considered an indication of the end of the paper's reliable life.

This is an additional test that we carry out as standard as a transformer ages. Degrading of a transformer's insulating papers is irreversible, so this test is a key tool in identifying where the asset is in its current life span. Please also see https://www.emepowersystems.co.uk/news/benefits-of-furans-testing

In Summary

Regular testing, analysis, and recording of results can provide a basis for interpreting the overall health and condition of transformers. This helps to prolong the assets' lifespan, avoid any catastrophic failures, and identify problems before they happen - helping our customers save money and manage their high voltage assets safely throughout their life span.

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