Electric power transformers are one of the main components of the myriad of complex equipment relied upon by power plants, substations, converter devices and many other industrial enterprises. The importance of transformers cannot be understated as electricity drives the modern world of business and commerce.
Transformers, depending on their type and individual specifications, are capable of operating in a variety of conditions and under varied loads. Based on the fact that transformers are an efficient and vital tool for energy conversion, it is very important to ensure the reliability and continuous trouble free service of electric power transformers.
Even under constant supervision however, an operator cannot always avoid unforeseen and unplanned breakdowns and damage to their transformer equipment. At least 80% of all known causes of the failure of electric power transformers involved oxidation of the transformer insulating oil also known as the transformer’s liquid insulation.
The most common form of damage to the average transformer is the damage done to the high-voltage oil-filled bushings. The cause of the damage is usually water and moisture.
Humidified Oil (high water and moisture content) can attack and deteriorate the transformers solid insulation properties leading to catastrophic transformer failure and disruption of electric power service.
Another type of transformer failure is a violation of the contact system. The failure can arise from the improper adjustment of contacts
The most severe consequences however, comes from damage to the solid insulation and transformer windings caused by sludge and other deposits of contaminated transformer oil that remain in the windings and solid insulation. This causes weakening and the occurrence of “creeping discharge” and subsequent transformer breakdown.
And finally, you should pay attention to the fact that there are inverse processes that cause damage to certain systems related to the content of the oil flow as they can adversely affect its performance and will cause oxidation. For example, damage to the oil pump may lead to the ingress of metal particles and other contaminants into the transformer oil.
If the transformer’s rubber seals fail, the oil will get wet and become filled with unwanted moisture. Water and moisture are two of the main catalysts in premature transformer aging.
To determine the level of contamination of the working fluids inside your electric power transformers, and to calculate the probability of failure, an analysis of the oil and its contents must be carried out on the transformer oil. Oil sampling and analysis of transformer oil should be performed every one to three years depending on the oil capacity of transformer.
If the test results of the oil analysis were significant, the next step will be to schedule transformer maintenance that will remove the contamination from the insulating oil.
The tests are conducted on the basic parameters of transformer oil specified in the regulations and the recognized basic performance quality of the oil itself.
Transformer oil is tested for dielectric strength, color, the presence of gas, water, mechanical impurities, additives, acids and alkalis. The analysis can also test the gas content of the oil.
One of the more essential performance characteristics of transformer insulating oil is the flash point of the oil. The lower the flash point, the greater the volatility and risk of combustion and explosion. As the oil deteriorates through evaporative decomposition, the viscosity will increase along with an increase in the content of explosive gases.
To determine the flashpoint of transformer oil, it is poured into a closed vessel and then heated. Fumes generated during such testing are mixed with air and will flare up when brought near a flame or when triggered by an electric spark. By checking the temperature of the flash and the composition of accumulated gases, the operator can accurately identify the nature of the internal damage of the transformer and the flash point of the oil.
The reverse of checking the flash point, is determining the pour point. It is a test of the oil’s ability to flow at low temperature extremes. If oil cannot flow, it will not be able to transfer heat and prevent harmful contaminants from damaging the solid insulation. Additionally, oil that cannot flow due to extreme cold will cause damage to oil pumps and other key components of the electric power transformer.
Checking the oil for the all important “Acid Neutralization” number is arguably one of the most important aspects of any oil analysis testing program. It will reveal the amount of sodium and potassium, (as expressed in milligrams) that is necessary to neutralize the free acids in 1 gram of oil. This indicator partially characterizes the level of oil aging. Once the acid number goes above 0.08, the oil must be processed to remove harmful contaminants.
The remaining tests of transformer oil are merely complementary. Their rates are not standardized. The density of oil is determined by a hydrometer. Statistical and dynamic viscosity is measured using a viscometer.
On the basis of these oil tests, it is possible to assesses the current performance characteristics of the oil and condition of the solid insulation. The testing results will allow the operator to determine and prepare the necessary cleanup and recovery plan for the oil and the transformer.
Maintenance control processes and timely filtration and replacement of transformer oil have become greatly automated using a variety of equipment and complex oil processing systems. Oil filtration is the process of removing mechanical impurities and resinous compounds by passing the oil through a mesh screen or the porous walls of fine and coarse filters. Modern filters use metal and plastic mesh, felt, fabric, paper, composites and ceramics as filter mediums.
The quality of the cleaning is increased by increasing the number of strainers and the introduction of a second stage of filtration. A quality filtration system will also absorb moisture, dust, fibers, carbon black, and other elements of oil aging.
Through the use of automated filtration equipment for purification of transformer oils such things as solids, free and dissolved water, and dissolved gas can be efficiently removed from the insulating oil.
The filtration equipment used for purifying and regenerating transformer oils must meet certain performance criteria:
- Clean the oil filter in a single cycle;
- Substantially prolong the life of the transformer oil;
- Have a universal use in various environments (outdoors or indoors) and have the mobility to serve a variety of industrial and remote locations; and
- Be easy to maintain and operate.
The timely and efficient performance of transformer preventive maintenance will prevent transformer failures and will extend the service life of your valuable electric power equipment.