Oil test services

ENGIS offers a wide range of Laboratory services based on the rich and global experience of Doble Engineering. Doble Materials Laboratory, established in 1933, is staffed by dedicated, experienced chemists and supported by engineering personnel knowledgeable in apparatus diagnostics. We are acknowledged for rendering dependable power transformers oil testing services in Israel.

The Doble Laboratory can provide answers and solutions to your problems based on quality data from a wide scope of testing capabilities and rich experience in apparatus diagnostics. We can help you develop the most cost-effective testing program for condition assessment or help identify and solve apparatus problems. All test reports include an analysis of the data and recommendations for remedial action, if warranted.

Routine oil tests for Power Transformers:

Dissolved Gas Analysis

The most important test that can be done on the liquid insulation of a transformer is an annual Dissolved Gas Analysis (DGA). This test can give an early indication of abnormal behavior of the transformer. As the name implies, this test analyzes the type and quantity of gases that are dissolved in the transformer oil.


The acidity test is used to estimate the total acid value of the transformer insulating liquid. As acid values increase (usually due to oxidation of the oil), the insulating quality of the oil decreases. In general, acidic by-products produce increased dielectric loss, increased corrosivity, and may cause thermal difficulties attributable to insoluble components called “sludge.”


Determination of the color of petroleum products is used mainly for manufacturing control purposes. It is an important quality characteristic since color is readily observed by the user of the product. In some cases, the color may serve as an indication of aging and presence of contaminants. However, color is not always a reliable guide to liquid quality and should not be used as a stand-alone test for determination of contamination

Water Content

The water content test detects the moisture content in parts per million of the liquid insulation. The electrical characteristics of an insulating liquid are dramatically affected by its water content. A high water content may make a dielectric liquid unsuitable for some applications because a deterioration in properties such as dielectric breakdown voltage will occur. This test is suitable for evaluating filtration.

Breakdown Voltage

The dielectric breakdown test is a physical test that measures the breakdown voltage of an insulation liquid. The dielectric breakdown test serves as an indicator to the presence of contaminating agents such as water, dirt, moist cellulosic fibers, and conducting particles in the insulating liquid. One or more of these items present in significant concentrations will contribute to a low dielectric breakdown value.

Dissipation Factor (Tan Delta)

A power factor (dissipation factor) test measures the dielectric losses in the liquid and hence the amount of energy dissipated as heat. The laboratory normally performs this test at two temperatures, 20 degrees C (68 degrees F) and 100 degrees C (212 degrees F), boiling. By testing the oil at a standard temperature, the test results can be compared to standard values. Power factor test results can help reveal the quality and the integrity of the insulation liquid. This information can form the basis for making a judgment on whether it’s suitable for a transformer to continue in service. The screen test can be used as a maintenance test for determining when a filtering or change of the transformer liquid is in need.

Volume Resistivity

Volume resistivity is the resistance to leakage current through the body of an insulating material. The higher the volume resistivity, the lower the leakage current and the less conductive the material is.

Furanic Compounds in Oil

Furanic compounds are generated by the degradation of cellulosic materials used in the solid insulation systems of electrical equipment. These compounds are oil soluble to an appreciable degree which leads to migration into the insulating liquid so that high concentrations or unusual increases in the concentrations in oil may indicate cellulose degradation from aging or incipient fault conditions.

Interfacial tension

The interfacial tension test of electrical insulating fluids is an indicator of the presence of polar compounds. These compounds are considered by some to be an indicator of contaminants of oxidation or deterioration of the materials of transformer construction.

Antioxidant Inhibitor

Mineral oil insulating fluids undergo oxidative degradation in the presence of oxygen to give a number of oxidation products. The final products of oxidation are acidic materials that can affect the characteristics of the insulating fluid as well as cause damage to the components of the electrical unit. One way to prevent these types of reaction is to incorporate an oxidation inhibitor that will interrupt and terminate the free radical process of oxidation


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Doble Lab oil tests capability, Press here