Take the next step.

Request a quote for our quality-assured transformer analysis and testing services, and we will get back to you in the next couple of business days.

Transformer oil analysis

Protecting the heart of your electrical systems 

Fluid testing for oil-filled transformers helps ensure the reliability and safety of critical electrical assets. Insights on oil health and contamination, and the detection of possible faults, help drive informed decisions that maximise transformer life and support safety measures.

transformer oil testing 1

The ALS difference

At ALS, we provide test results quickly and hassle-free with sample turnaround times of less than one week — because early detection of faults is critical to helping ensure assets remain online. 
We offer 24/7 data availability through the ALS Webtrieve™ online portal, which offers various integrations with our clients’ databases. Our test reports are easy to read and utilise the latest IEEE guidelines to provide expert interpretations at no extra charge.
With ALS’ over 30 years of experience in the transformer fluid testing industry, your assets are in good hands.

La diferenciación de ALS

Transformer oil tests and what they measure

Transformer fluids can be Mineral Oil (Paraffin and Naphtha based), Silicone Oil, and Natural or Synthetic Esters. It is common to use some different methods for testing because of the elemental differences.

Care should be taken when sampling transformer fluid and should be performed by a trained operator. Sampling for Dissolved Gas Analysis (DGA) requires a special sampling syringe, which ALS can help provide.

  • Color (D1500)

    An observation of the darkening of the oil by comparing it to previous samples of oil from the same transformer.

  • Dielectric breakdown voltage (D1816)

    Measures the voltage at which the oil fails electrically, which is indicative of the amount of contaminant (usually moisture) in the oil .

  • Interfacial tension (D971)

    Measures the presence of soluble contaminants and oxidation products in transformer oil. A decreasing value indicates an increase in contaminants and/or oxidation products within the oil.

  • Water Content (moisture) (D1533)

    Measured in parts per million (ppm) using the weight of moisture divided by the weight of oil. Moisture content in oil lowers the insulating dielectric strength.

  • Dissipation factor (Power Factor) (D924)

    Indicates the dielectric losses of the oil, or energy that is dissipated as heat. Useful for measuring changes within the insulating oil resulting from contamination or deterioration.

  • Acid number (D974/D664)

    New transformer oils contain practically no acids. The acidity test measures the content of acids formed by oxidation and contaminates.

  • Oxidation inhibitor content (D2668)

    Added to some oils to help protect the paper insulation from oxidation.

  • Resistivity (D1169)

    Measures the electrical insulating properties of transformer oil.

  • Dissolved gas analysis (D3612)

    Identifies various gas levels that are present in transformer insulating oil. Different gasses dissolved in the oil indicate various types of thermal and electrical stress occurring within the transformer.


    Corona discharge Low energy discharges create methane and hydrogen and smaller quantities of ethylene and ethane.
    Arcing Large amounts of hydrogen or acetylene or minor quantities of ethylene and methane can be produced.
    Overheated Oil Overheating oil will produce methane and ethylene (300ºF) or methane and hydrogen (1,112ºF). Traces of acetylene might be created if the unit has electrical contacts or if the problem is severe.
  • Polychlorinated biphenyls (PCB) content (D4059)

    Used for measuring PCB content in electrical equipment.

  • Furanic Compounds (D5837)

    Used as an indirect measurement of the condition of the paper insulation by measuring the amount of Furanic compounds within the oil. Furanic compounds are an intermediate breakdown product from overheating of paper in an anaerobic environment.

  • Visual examination (D1524)

    This test method for visual examination is applicable to mineral oils of petroleum origin that have been used in transformers. It is used to determine if the sample has been taken correctly, with the appropriate amount of flushing.

Related topics & resources

oil filled transformer

Increase transformer lifespan

Properly maintained transformers should not have to be replaced for 50 years or more


Routine fluids analysis

The key to transformer maintenance

A large power substation stands against a bright, clear, sky.

Calculate your ROI

Find out the true cost-benefits of a properly implemented Transformer Oil Analysis program