These are the following tests that we offer:

Dielectric breakdown ASTM D877M and D1816

The dielectric breakdown voltage in insulating oil measures the ability of the oil to withstand a certain voltage level without generating a spark. The voltage at which the rupture occurs between the two discs is done in a controlled environment at the laboratory. The purpose of this test is to determine if the oil contains any electrical conducting contaminants. These contaminants could be: water, cellulose fiber dust or particulate material. A high dielectric breakdown voltage does not necessarily mean the oil is free from these contaminants.


The electrodes for the ASTM D877 test are flat discs, not representative of the transformers structure. Even when the discs for the D1816 do not duplicate the characteristic of the transformer, they resemble them to a certain degree. The D1816 test has a higher sensibility to dust, particles and dissolved moisture; it evaluates the changes that may occur within a transformer.

Interfacial Tension ASTM D971

This method covers the measurement under non-equilibrium conditions of the interfacial tension that the insulating oil has against water. The interfacial tension is a measurement of force of attraction between the molecules of the two fluids, expressed in millinewtons per meter “mN/m”. This method is an excellent mean of detection of soluble polar contaminants within the oil and products of oxidation in oils.


Specific Gravity ASTM-D-1298

Relative density is the proportion of the two weights of equal volume of oil and water, tested at 15°C. The relative density is significant in the determination of the solubility for certain applications: in cold climates, ice can form within the equipment exposed to subzero conditions. When considered with other properties of the oil, it can be used as a quality indicator of the oil.


If the readings of the hydrometer are above 0.91, it is possible that the insulating oil contains contaminants, possibly Askarels (PCBs); if the reading is below 0.84 the oil may contain paraffinic characteristics.

Neutralization Number ASTM-D-974

The acid number, or neutralizing number, of an insulating liquid is the mean of determination for acidic components. In new oil, any trace of acidity is probably residue from the refinement process. If the fluid is in service, the acid number will indicate an oxidation process taking place. It can be used as a guide to establish when the oil has to be treated for regeneration or changed. ASTM D974 is the standard method using color indicators during the titration of the acids within the sample and Potassium hydroxide (KOH). The acid number is expressed in milligrams of KOH used to neutralized grams of a sample: mgKOH/g.


In transformers these organic acids are supremely harmful for the insulating material and can cause oxidation of the metal pieces when moisture is present. An increase in the acid number is indicative of oil deterioration. The formation of muds will be an inevitable result when the acid number increase is overlooked.

Moisture content ASTM-D-1533

Moisture may be present in insulating fluids in many forms. Free water can be detected through visual examination, a cloudy sample or water droplets at the bottom of the bottle will be easily seen. The presence of free water can be solved with the oil filtering system. Dissolved water cannot be detected visibly, and requires means of physical or chemical quantification. Dissolved humidity can affect the dielectric breakdown in the oil; this determination is part of the other different factors such as the moisture saturation percentage, quantity and types of contaminants present in the sample.


This method helps determine the total moisture count as well as the dissolved moisture in the oil depending on the sampling and the conditions during the sampling.

Water absorbed or adsorbed in the solid insulation increases the decomposition rate of the solid insulation, shortening the life expectancy of the transformer. There is a direct relation between the paper and the water: if the moisture concentration (ppm) is doubled, the solid insulation (paper) is reduced by half. When the moisture levels are high, the transformer’s temperature may be high enough to allow an electric arc to happen due to the humid insulation, which will be a catastrophic failure.

Percent Saturation of water in oil IEEE C57.106-2006

The humidity is not very soluble in the presence of new and clean oil. The solubility increases at higher temperature. The saturation % is calculated with the concentration in part per million “ppm” and the temperature of the oil in the transformer. If the moisture is higher than the expected saturation % and the transformer is cooled significantly, part of the dissolved water will separate and will form drops of free water. These droplets will generate a condition that can cause a dielectric breakdown the instant it touches an energized conductor.

Percent Moisture by dry weight IEEE C57.106-2006

One of the main concerns is the moisture in the paper insulation, given that it deteriorates the insulating system prematurely which leads to a reduction of the life expectancy of the equipment. If the moisture is allowed to exceed these limits, the transformer will be in such bad condition that an electrical arc will be formed at normal working temperatures within the transformer. %M/DW (Moisture % by dry weight) is also calculated.

Color ASTM-D-1500

The oil has a characteristic color that should be clear, allowing visual inspection of the internal structures within the tank. Any changes in the oil indicates a deterioration or oil contamination.

Visual Inspection ASTM-D-1524

The oil sample is examined under a white light to check if there is any cloudiness, particles, visible sediments or muds, carbon, free water or any other element that should not be there. The oil should clear and homogenous. In order for an oil to be acceptable it should be a clear and bright and free of contaminants.


PCBS – Chlorine concentration

Clor-n-Oil 50 PPM

Clor-n-Oil is a fast and easy method to test insulating fluids (transformer oil) and check for chlorinated compounds within the sample. There are three different limits for testing within the Clor-n-Oil range: 20 ppm, 50 ppm and 500 ppm. In order to eliminate false negative results, Dexsil specifically targets the Aroclor 1242 in Clor-n-Oil. Aroclor 1242 has the less quantity of chlorine (42% by weight) of all Aroclor found in insulating fluids. The results are indicated by colour, a purple shade indicates low or no concentration within the sample.


Dexsil L2000DX Analyzer o

The L2000DX is based on the same testing method as the Clor-N-Oil, however, instead of a colour indicator, it measures, by ion quantification, the specific concentration within the sample, using a special electrode. The range of measurement is from 2 up to 2000 ppm.


Gas Chromatography ASTM 3612 Method C

As the transformer is exposed to electric and thermal stress it will generate combustible gas in the transformer. The insulating materials, the oil as well as the cellulose will decompose as consequence of such stress, generating gas.


The presence of the individual gases extracted from the oil and analyzed, reveal a type and grade of condition that are caused by the generated gas. The rate and the quantity of the gas generated is very important. The process of normal aging generates certain gases; however, these increase at low rates. The conditions of failure or failure of recent formation cause immediate changes and can be observed in the dissolved gas concentration.

More importantly, the vast majority of these failures offer early evidence of a failure or a problem in development, thereby they can be detected by analyzing the transformer oil. Gas chromatography (GC) is by far the best method of extraction and analysis of combustible gas, is a qualitative method of gases dissolved in oil.

Furan compounds ASTM D5837

Cellulose is an organic material integrated by polymer chains formed by glucose molecules linked as fibers. Cellulose, in KRAFT paper, combined with insulating oil, form the electrical and mechanical insulating system. However, the paper may suffer from ruptures and deterioration, this last event can be due to normal aging of the insulation or rapid aging due to external factors: these include increasing operational temperatures in the transformer, high moisture levels and oxidation exposure due to high acidity.

One of the methods used to supervise the deterioration of the cellulose is through technique of polymerization (DP). Is a measurement of the length of the cellulose chain and requires a sample of the paper from the transformer. There are, however, other products of deterioration of cellulose that dissolve in the insulating oil, called furans. A furan analysis can be done without the need to open the transformer and can be kept in service, contrary to the removal of paper.

Furans can only be found when paper deterioration is taking place, which gives the advantage of the analysis, offering the exact condition of the solid insulation in a transformer; it generates five components that can be detected: 5-hydroxymethyl-2-furaldehyde, furfuryl alcohol, 2-furaldehyde, 2-acetylfuran and 5-methyl-2-furaldehyde. The principal component for the analysis is 2-furaldehyde, measured in ppb (parts per billion), determined by liquid chromatography. Under the polarization grade 250, the transformer cannot withstand short-circuit stress.