Transformer Oil Degassing Plant
Transformer oil degassing is a process required for high-voltage electrical equipment. During the service life of transformers, the insulation system undergoes various physicochemical changes that lead to the formation of decomposition products — solid, liquid, and gaseous substances. These changes are intensified when the insulation becomes moist. Both solid insulation materials based on cellulose (such as paper and cardboard) and transformer oil release gases during gradual aging. Among these gases are hydrogen, low-molecular hydrocarbons, as well as carbon monoxide and carbon dioxide, which appear as a result of cellulose oxidation.
The formation of gaseous decomposition products in insulation materials when exposed to electric fields, discharges, and heat is an inevitable phenomenon for any operating electrical device. The gases dissolved in the oil of power transformers may include methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), acetylene (C₂H₂), propane (C₃H₈), propylene (C₃H₆), butene (C₄H₈), and butane (C₄H₁₀). When insulation damage occurs, the gas formation rate increases sharply, and the composition of gases changes significantly. The presence of a gaseous phase in the insulation complicates the operation of high-voltage equipment and, in turn, further accelerates gas formation.
Gases may enter transformer oil not only from the surrounding air, but also as a result of accelerated insulation aging. The primary cause of this process is transformer overheating. When the oil decomposes due to overheating, it produces gaseous substances such as ethane, methane, and hydrogen, which are highly soluble in the insulating liquid. If oil-impregnated paper decomposes, gases such as carbon dioxide, hydrogen, and carbon monoxide develop in the oil. Furthermore, gaseous substances can form in transformer oil due to partial discharges within the insulation.
Causes of Gas Formation in Liquid Dielectric
The main reason for the oxidation and degradation of dielectric liquid is the presence of air. Oxygen initiates chemical reactions that cause the breakdown of oil molecules and the formation of acidic and gaseous products. Therefore, transformer oil degassing plays a key role in halting these destructive processes. By removing gases and moisture, it is possible to extend the operational life of the transformer and ensure the stable dielectric strength of the insulation system.
The solubility of gases in transformer oil varies depending on temperature and pressure. For instance, at 77 °F and a pressure of 736 mmHg, oxygen from the air can dissolve in oil up to about 3%, while nitrogen has a solubility of nearly 7%. This means that without proper degassing, the oil continuously absorbs gases from the atmosphere, leading to its deterioration and an increased risk of dielectric breakdown.
The Process of Transformer Oil Degassing
Transformer oil degassing occurs during the oil dehydration process. Specialized systems — such as DC-type degassing units — are used to remove gases from transformer oils. These units perform not only degassing, but also purification from solid particles, moisture removal, and transformer vacuuming. The operating range of these units covers oils with viscosities up to 70 cSt at a temperature of +50 °C.
The degassing process generally involves several stages:
- Heating — the oil is preheated to reduce its viscosity and enhance the release of dissolved gases.
- Vacuuming — the oil is exposed to a vacuum environment where the pressure is reduced, enabling the extraction of air and gases from the liquid.
- Degassing and Dehydration — under vacuum, gases and moisture are efficiently removed from the oil.
As a result of transformer oil degassing, the purified oil achieves the following quality parameters:
- Gas content — not more than 0.1 % by volume.
- Moisture content — not more than 5 ppm (g/t).
- Purity grade according to ISO 4406 — -/14/12.
These parameters ensure that the regenerated oil fully restores its insulating and cooling properties, which guarantees safe and reliable operation of transformers.
DC Transformer Oil Degassing Units
The DC transformer oil degassing systems are designed for both fixed-type and mobile applications. The units can service power transformers directly on-site, performing oil filtration, moisture removal, and transformer vacuuming simultaneously. Advanced models are equipped with automated control systems, temperature sensors, and vacuum regulators, which make the process fully controllable and efficient.
By maintaining optimal operating conditions, transformer oil degassing units prevent oxidation, reduce the risk of dielectric breakdown, and extend the service life of both the oil and the transformer insulation.
Transformer oil degassing improves the reliability and service life of transformers. The purity and stability of transformer oil are ensured by removing gases and moisture therefrom, thereby preventing the premature degradation of insulation. As a result, the transformer operates at lower temperatures, lasts longer, and requires less maintenance over time.