Services - Dielectric Oil Laboratory

Laboratório de Óleo Dieléctrico Periodic testing to insulating oil is the only means that the Maintenance Manager has to diagnose the equipment condition, allowing him to take the necessary corrective measures in order to maintain the operability of these assets. We need to underline that while considering general maintenance costs, the cost of the testing is quite insignificant.

AMBICARE has its own laboratory, properly equipped, where it holds physical-chemical tests to insulating mineral oils.

Is not possible through a single test/analysis procedure to make the diagnosis of the condition of solid insulation and insulating oil of a transformer in service; notwithstanding, it is required the completion of a set of test/analysis procedures.


The results of the various test/analysis procedures should not be considered isolated using default parameters set forth by the standards; results should be interpreted taking into account and in conjunction with the equipment history, in order to diagnose the transformer condition and allowing for the recommendation of future corrective maintenance actions, thus ensuring the extension of its service life.
The test/analysis conducted by the laboratory are the following:


Trial Standard Detailed Information
Breakdown Voltage IEC 60156 Indicates the presence of conductive contaminants, fibers and free water.
(mgKOH/g of oil)
IEC 60296 or
ASTM D664-89
Indicates the degree of oil acidity. A high value can cause problems due to corrosion of the metal parts and the formation of salts with metal ions that will affect the electrical properties of the oil. The acids also increase the solubility of water in oil.

Water content

(H2O ppm)

IEC 60814
Indicates total concentration of water dissolved in oil and can provide an indication of the amount of water in paper.
About 70% of transformers failures are caused by high water content.

Interfacial tension (mN/m) 

ASTM D 971 In combination with the acid value and Dielectric Dissipation Factor it can provide an early warning pointer of the beginning of an oil decay. Indicates the presence of sludge in oil. 
Dielectric Dissipation Factor (tan δ) at 90º IEC 60247 Oil quality indicator as an insulator. High values indicate the presence of polar compounds and other contaminants resulting from the degradation of the oil/paper.
Colour ISO 2049 A sudden change of colour within a year may indicate transformer problems.
Appearance IEC 60296 The oil turbidity indicates the presence of free water and any impurities, such as fibers or cellulose particles in the oil.
PCB Screening USEPA SW-846
Qualitative test (Colorimetric). It checks the existence of PCBs in insulating oils. In the case of a positive result, it requires confirmation by the method below. In the case of negative result, there is the certainty that the oil does not contain PCBs.
Gas Chromatography for Quantification of PCBs (ppm) IEC 61619 or
EPA 600/4-81-045
It determines the concentration of PCBs. All equipment shall be subject to a screening test and/or to an analysis for determination of PCBs in accordance with Portuguese Decree-Law No. 277 of July 23, 1999.
Combustible Gases (ppm) IEC 60567-60599 It is carried out to evaluate the physical condition of the transformer with reference to such factors as electric shocks and paper deterioration.
Furanic compounds (ppm) IEC 61198 It is carried out to assess the state of degradation of solid insulation.
Inhibitor content IEC 60666 Analysis to perform only to inhibited oils. Determines the concentration value of oxidation inhibitor. Prevents oil oxidation phenomena.
Sediments and sludges IEC 61125 Analysis of determination of sludge and sediments in oil. The existence of sediments and sludge in oil may decrease the dielectric properties and limit the function of oil cooling by blocking the heat channels transmission.
Density at 20ºC ISO 3675 Also called density test determination, allows pinpointing the type of oil and preventing its usage in strongly adverse climates.
Kinematic viscosity at 40° C ISO 3104 Its value allows you to control the ability of oil heat dissipation. The viscosity value increases with oil aging and oxidation.
Flashpoint ISO 2719 A low flashpoint value can indicate the presence of fuel volatile substances in oil, which may result from contamination of a solvent.
Potentially corrosive / Corrosive sulphur ASTM D 1275-06 or
IEC 62535
Determination of the existence of molecules containing sulphur in oil that normal operating temperatures can cause corrosion of metal surfaces by formation of sulphur sulfides.


Go to top