English 
Portuguese The quality control of insulating oil in electrical system equipment
The types of tests
- Water content: measures the amount of water present in the insulating oil and is performed by means of the Karl Fischer test.
- Dielectric strength: measures the capacity of insulating oil to isolate electric current and is evaluated through the dielectric strength test.
- Acidity: measures the level of acidity of the insulating oil and is evaluated using the total acidity test.
- PCB content: evaluates the presence of toxic organic compounds known as PCBs (polychlorinated biphenyls) and is carried out through laboratory analysis.
- Particles and sediments: measures the amount of particles and sediments present in the insulating oil and is evaluated using the particle count test.
It is important to note that in addition to the obligations established by ANEEL, the companies must follow the technical standards established by ABNT (Brazilian Association of Technical Standards) for quality control of the insulating oil and to carry out the tests. In Brazil, there are standards that regulate the quality control of insulating oil in electrical system equipment, such as:
- NBR 10576:2017 - Mineral insulating oil for electrical equipment - Guidelines for supervision and maintenance
- ABNT 7274:2012 - Interpretation of gas analysis of transformers in service
In accordance with what has been established, COTESA Engineering constantly monitors the quality of insulating oil in equipment, using national and international standards and consolidated methods, such as Duval's interpretations and multi-criteria methods for decision support.
In this way, information of great importance is provided for decision making related to preventive maintenance and, in this way, minimizing spending on corrective maintenance or failures that lead to great losses.
The company has more than 3.1 thousand insulating oil analysis results in its database, in addition to the monitoring of more than 460 transmission or generation clients' equipment.
We ensure the reliability of electrical equipment by adopting consolidated insulating mineral oil diagnostic techniques and decision support methods based on accurate and reliable data.
Contaminants in oil, such as water, particles, and gases, can affect the oil's ability to insulate electrical current, reduce its ability to dissipate heat, and increase equipment corrosion and wear. In addition, contaminated oil can lead to equipment failure, interruption of power supply, and damage to the environment.
Quality control of insulating oil involves regular analysis of the oil to detect the presence of contaminants and assess the quality of the oil. These analyses include tests for acidity, water content, flash point, resistivity, and more. Based on the results of these analyses, preventive measures can be taken, such as filtering and dehydrating the oil, to avoid contamination of the equipment and prolong its life.
There are standards that establish the minimum requirements for quality control of insulating oil and define the test procedures to be followed. It is important to follow the standards to ensure the reliability of the tests and to ensure the integrity of the equipment in the electrical system.
In addition, the National Agency of Electrical Energy (ANEEL) establishes the rules for the provision of electrical energy transmission services in Brazil, through Normative Resolution No. 906/2020. This standard establishes the mandatory performance of physical-chemical and dissolved gas tests in transmission equipment, in addition to other preventive maintenance.
The physical-chemical test evaluates the physical and chemical properties of the insulating oil, such as density, viscosity, flash point, among others. These tests are important to verify the integrity of the insulating oil and detect possible changes in its properties.
The test for dissolved gases is used to detect the presence of gases in insulating oil, such as oxygen, nitrogen, hydrogen and carbon dioxide, which may indicate the presence of defects in electrical equipment. The analysis of these gases allows the identification of the types of defects that may be present in the equipment, such as partial discharges, insulation failures, among others.
In addition to the tests mentioned above, there are other important tests for quality control of insulating oil in electrical system equipment.