Our laboratory of insulating liquids is made up of highly experienced professionals and provides a true diagnostic tool regarding the condition of transformers and tap changers under load. In the last years an important amount of oil analysis have been made, diagnosing the state of transformers for the main players in the energy market.
We highlight the equipment of the laboratory:
The tests we do in our laboratory, necessary to determine the quality of the oil are:
Visual aspect: Provide quick information, valuable and easy to determine. This test can reveal the presence of clear water or impurities, such as fibers or solid particles.
Observation may suggest the need for additional laboratory testing. The visual appearance in a good oil should be bright and transparent without solids in suspension.
Color – ASTM D-1500 : This test is expressed with a numerical value and it is based on a comparison by light through a disk that has a series of glasses of standard color. It is not a critical property, but may be useful for a comparative evaluation.
Color changes normally occur in very long periods of and provide an indication of deterioration and/or oil contamination.
Density – ASTM D-1298: The density defines the type of oil and detects the important modifications of its composition. In cold climates, the oil density may be important in determining the suitability of its use.
Interfacial tension – ASTM D-971: This test is the most important physical determination which is made to insulating oils. It is a measure of the forces of attraction between the molecules of two not miscible fluids.
The interfacial tension is an excellent test to detect soluble contaminants and oxidation products in insulating oils.
Moisture Content – ASTM D-1533: The most commonly used test method for determining moisture in the oil is the Karl Fisher. This method is based on the iodine reduction which is generated electrochemically.
Water is not only harmful to oil because it increases its electrical conductivity, but is also a highly corrosive element to ferrous metals and thus forming iron oxide that when dissolved in the oil makes it even more conductive.
Acidity index – ASTM D- 974: This test is used to evaluate the relative change in an oil during use under oxidizing conditions.
When mineral oil is new, contains very low levels of acidic constituents and the number of neutralization increases as oil degradation occurs. A used oil that has a high number of neutralization indicates that the oil is oxidized or contaminated with substances such as varnish, paint or other materials.
Power Factor – ASTM D-924: This property is a measure of the dielectric losses in an oil and, therefore, the amount of energy dissipated as heat. Low power factor values indicate low dielectric losses and a low polar soluble ionic level, or colloidal contaminants. These features can be useful as a means of quality control and as an indication of changes in the oil in service, as a result of deterioration and/or contamination.
When the deterioration of an oil begins, it is possible to detect an increase in the power factor at the beginning of the oxidation process, followed by a certain time by an increase.
Volumetric Resistivity – ASTM D-1169: It is a complementary test to the Power Factor or Dissipation which makes it possible to determine the presence of conductive pollutants particles.
A low volumetric resistivity usually indicates the presence of contaminating particles in the oil.
Dielectric strength – ASTM D-1816: The dielectric strength is the maximum potential gradient which can withstand the oil, without occurring the disruptive discharge.
It is also the ability of a liquid to withstand the electrical stress without a fault occurring.
Indicates the presence of pollutants, such as water, soil, cellulose fibers, mud, sludge or conductive particles in the liquid. When low dielectric strength values are found, one or more of these pollutants may be present in the oil, however, a high break value does not necessarily indicate the absence of these pollutants.
Chromatography – ASTM D – 3612: The analysis of dissolved gases is based on the separation of components interacting with the stationary phase or medium. If these interactions are different from each other, so will the speeds with which the components will cross the medium.
Using this method allows you to obtain advance notice of a fault and indicate the nature and location of this. When a transformer presents incipient problems or faults like bows, partial discharges which can not be detected by electrical tests, the analysis of dissolved gases in the oil is a valuable tool which provides more information on the fault.
Corrosive Sulfur – ASTM D1275- 06: Insulating oils are continuously in contact with metals, such as copper, which is subject to corrosion, so the presence of free sulfur and corrosive is harmful in the deterioration of these metals, depending largely on the quantity, time factors and temperature.
PCB – ASTM D- 4059 : This substance may be the best insulating fluid known for its excellent dielectric characteristics, thermal and chemical stability, but it turned out to be carcinogenic and therefore harmful to human health and the environment, reason why today its use is prohibited by international environmental authorities.
Furans – ASTM D-5837: Consists of determining in the insulating liquids the degradation products of cellulose materials, such as paper, cardboard and cotton material, insulation materials that make up electrical equipment.
The furanic compounds are soluble in oil. High concentrations or unusual increases in the concentration of furanic compounds in the oil may indicate degradation of cellulose, due to the aging of the equipment or by incipient failures.
DBDS : The phenomenon of corrosion on metal surfaces of the transformer is a common phenomenon and in some cases directly related to failures detected in this type of electrical equipment.
Recently, corrosion has been linked with the presence of specific compound called DBDS (Dibenzyl disulfide). In fact, in the latest version of the regulation IEC 60296:2012, “New mineral insulating oils for transformers and switchgear”, it makes reference to this compound, establishing that its value is not detectable, in other words, that does not exceed the concentration of 5mg/kg.