As a supplier of Hermetically Sealed Oil Filled Transformers, I've witnessed firsthand the critical role that oil plays in the performance and longevity of these transformers. The oil in a hermetically sealed oil filled transformer serves multiple functions, including insulation, cooling, and arc quenching. However, over time, this oil can degrade, which can have serious implications for the transformer's operation. In this blog, I'll discuss the signs of oil degradation in a hermetically sealed oil filled transformer, helping you to identify potential issues before they lead to significant problems.
Changes in Physical Properties
One of the most obvious signs of oil degradation is a change in its physical properties. Fresh transformer oil is typically clear and has a light amber color. As the oil degrades, it may become darker, cloudier, or even develop a sludge-like consistency. These changes can be caused by a variety of factors, including oxidation, thermal stress, and the presence of contaminants.
Oxidation is a chemical reaction that occurs when the oil comes into contact with oxygen. This reaction can be accelerated by high temperatures, which are common in transformers. As the oil oxidizes, it forms acids and other byproducts that can cause corrosion and damage to the transformer's internal components. The formation of these byproducts can also cause the oil to thicken and become more viscous, reducing its ability to flow and dissipate heat effectively.
Thermal stress can also cause the oil to degrade. When the transformer operates at high temperatures for extended periods, the oil can break down and form gases and other volatile compounds. These compounds can accumulate in the transformer and cause a variety of problems, including reduced insulation resistance, increased partial discharge activity, and even the formation of explosive mixtures.
Contaminants, such as water, dirt, and metal particles, can also cause the oil to degrade. Water can react with the oil and form acids, which can corrode the transformer's internal components. Dirt and metal particles can act as abrasives, causing wear and tear on the transformer's moving parts. These contaminants can also reduce the oil's insulation resistance and increase the risk of electrical breakdown.
Changes in Chemical Properties
In addition to changes in physical properties, oil degradation can also cause changes in the oil's chemical properties. These changes can be detected through laboratory analysis of the oil sample. Some of the most common chemical changes associated with oil degradation include changes in the oil's acidity, moisture content, and dissolved gas content.
The acidity of the oil is an important indicator of its degradation state. As the oil oxidizes, it forms acids that can cause corrosion and damage to the transformer's internal components. The acidity of the oil can be measured using a titration method, which involves adding a known amount of base to the oil sample and measuring the amount of acid that is neutralized. A high acidity level indicates that the oil has degraded and may need to be replaced.
The moisture content of the oil is another important indicator of its degradation state. Water can react with the oil and form acids, which can corrode the transformer's internal components. Water can also reduce the oil's insulation resistance and increase the risk of electrical breakdown. The moisture content of the oil can be measured using a Karl Fischer titration method, which involves adding a known amount of reagent to the oil sample and measuring the amount of water that is present. A high moisture content indicates that the oil has been contaminated with water and may need to be dried or replaced.
The dissolved gas content of the oil is a third important indicator of its degradation state. When the oil breaks down, it forms gases such as hydrogen, methane, ethane, ethylene, and acetylene. These gases can accumulate in the transformer and cause a variety of problems, including reduced insulation resistance, increased partial discharge activity, and even the formation of explosive mixtures. The dissolved gas content of the oil can be measured using a gas chromatography method, which involves separating the gases in the oil sample and measuring their concentrations. A high dissolved gas content indicates that the oil has degraded and may need to be replaced.
Changes in Electrical Properties
Oil degradation can also cause changes in the oil's electrical properties. These changes can be detected through electrical tests of the oil sample. Some of the most common electrical changes associated with oil degradation include changes in the oil's dielectric strength, dissipation factor, and insulation resistance.
The dielectric strength of the oil is a measure of its ability to withstand electrical stress without breaking down. As the oil degrades, its dielectric strength can decrease, which can increase the risk of electrical breakdown. The dielectric strength of the oil can be measured using a high-voltage test set, which applies a high voltage to the oil sample and measures the voltage at which the oil breaks down. A low dielectric strength indicates that the oil has degraded and may need to be replaced.
The dissipation factor of the oil is a measure of its ability to dissipate electrical energy. As the oil degrades, its dissipation factor can increase, which can indicate the presence of contaminants or other problems. The dissipation factor of the oil can be measured using a capacitance bridge, which measures the capacitance and resistance of the oil sample. A high dissipation factor indicates that the oil has degraded and may need to be replaced.
The insulation resistance of the oil is a measure of its ability to resist the flow of electrical current. As the oil degrades, its insulation resistance can decrease, which can increase the risk of electrical breakdown. The insulation resistance of the oil can be measured using a megohmmeter, which applies a high voltage to the oil sample and measures the resistance of the oil. A low insulation resistance indicates that the oil has degraded and may need to be replaced.
Implications of Oil Degradation
Oil degradation can have serious implications for the performance and longevity of a hermetically sealed oil filled transformer. When the oil degrades, it can cause a variety of problems, including reduced insulation resistance, increased partial discharge activity, and even the formation of explosive mixtures. These problems can lead to electrical breakdown, which can cause damage to the transformer's internal components and even result in a complete failure of the transformer.
In addition to the potential for electrical breakdown, oil degradation can also reduce the transformer's efficiency and increase its operating costs. When the oil thickens and becomes more viscous, it can reduce the oil's ability to flow and dissipate heat effectively. This can cause the transformer to operate at higher temperatures, which can increase the risk of thermal stress and further oil degradation. The increased operating temperature can also reduce the transformer's efficiency and increase its energy consumption, resulting in higher operating costs.
Preventing Oil Degradation
Preventing oil degradation is essential for maintaining the performance and longevity of a hermetically sealed oil filled transformer. There are several steps that can be taken to prevent oil degradation, including proper installation, maintenance, and monitoring.
Proper installation is critical for preventing oil degradation. The transformer should be installed in a clean, dry, and well-ventilated area. The oil should be filled to the correct level, and the transformer should be properly grounded to prevent electrical interference.
Regular maintenance is also essential for preventing oil degradation. The transformer should be inspected regularly for signs of damage, such as leaks, cracks, and corrosion. The oil should be sampled and tested regularly to monitor its physical, chemical, and electrical properties. If the oil shows signs of degradation, it should be replaced or treated to prevent further damage to the transformer.
Monitoring the transformer's operating conditions is another important step in preventing oil degradation. The transformer should be operated within its rated capacity and temperature limits. The temperature, load, and other operating parameters should be monitored regularly to ensure that the transformer is operating under normal conditions. If the transformer operates under abnormal conditions, such as high temperatures or overloads, steps should be taken to correct the problem and prevent further damage to the transformer.
Conclusion
As a supplier of Hermetically Sealed Oil Filled Transformers, I understand the importance of maintaining the quality of the oil in these transformers. Oil degradation can have serious implications for the performance and longevity of the transformer, and it is essential to identify and address the signs of oil degradation as early as possible. By monitoring the physical, chemical, and electrical properties of the oil, and by taking steps to prevent oil degradation, you can ensure that your transformer operates safely and efficiently for many years to come.
If you are interested in learning more about our Oil Immersed Self Cooled Transformer, 10kv Oil Immersed Transformer, or Fully Sealed Oil Immersed Distribution Transformer, or if you have any questions about oil degradation in hermetically sealed oil filled transformers, please do not hesitate to contact us. We are always happy to help you find the right solution for your needs.
References
- IEEE C57.106-2018, Guide for Acceptance and Maintenance of Insulating Oil in Equipment.
- IEC 60422:2013, Mineral insulating oils in electrical equipment - Supervision and maintenance guide.
- ASTM D3487-17, Standard Specification for Mineral Insulating Oil Used in Electrical Apparatus.