Transformer Oil Purification

Regular transformer oil purification should be carried out to improve the operational reliability of oil-filled transformers. Mineral oil has been used in oil-filled transformers for almost a century due to its excellent electrical and thermal properties. Its high performance, good quality, and excellent technical and economic characteristics make mineral oil an ideal insulating and cooling fluid for high- and ultra-high-voltage power transformers. Although mineral transformer oil remains the most widely used insulating fluid, a number of problems are still associated with its use.

Types of Transformer Oils

Mineral Base Transformer Oils Mineral oil remains the most commonly used type of transformer oil. Despite its wide use, it has several disadvantages such as:

• Low Flash Point: typically below 284°F, increasing the risk of breakdown and fire during high-temperature operations.
• Environmental Concerns: mineral oil is non-renewable, difficult to biodegrade, and may pollute the environment in case of leaks.

Vegetable-Based Transformer Oils Derived from natural oils through processes such as pressing, refining, and modification, these oils are renewable and biodegradable. They offer:

• High Flash Point: often exceeding 572°F, which enhances safety.
• Good Electrical Properties: suitable for environmentally friendly applications. However, they also have disadvantages, including higher costs (3–4 times as high as those for mineral oil), higher water content, and limited operational experience.

Silicone-Based Transformer Oils Silicone oil is increasingly used in small-capacity transformers below 35 kV. Its benefits include:

• High Flash Point: reduces fire hazards.
• Low Freezing Point: ensures reliable performance in colder climates.
• Stable Viscosity: provides consistent performance across temperature ranges. Limitations include lower resistance to electrical discharges and reduced insulation strength under repeated voltage stresses.

Synthetic Ester Transformer Oils Known for their fire safety and environmental benefits, synthetic ester oils can biodegrade into carbon dioxide and water under the action of microorganisms. Key advantages include:

• Superior Oxidation Resistance: longer service life compared to mineral oils.
• High Moisture Tolerance: maintains insulating properties even under high humidity conditions. However, their strong affinity for water molecules and higher initial costs may limit widespread adoption.

Negative Factors affecting Transformer Oil during Operation

The deterioration of insulation in power transformers is caused by several major factors, such as: Thermal Aging High operating temperatures are among the primary contributors to the thermal aging of transformer oils. Heat accelerates the degradation of both the oil and the insulation materials, such as oil-impregnated paper, resins, and other composites. Prolonged exposure to elevated temperatures causes the oil to lose its insulating properties and become more prone to oxidation. For instance, research indicates that exceeding the nominal temperature limits can significantly shorten transformer service life. The stages of thermal aging include:

• Initiation: early degradation caused by initial heat exposure.
• Progression: accumulation of damage leading to decreased mechanical and electrical strength.
• Critical Stage: severe deterioration of the material that poses a risk of short circuits or other failures.

Without proper cooling, transformers experience accelerated degradation, which can potentially lead to catastrophic failure. Electrical Stresses and Surges Electrical overstress, such as voltage spikes caused by system switching, can significantly affect transformer insulation. These high-voltage surges can puncture the insulation, leading to arc discharges. This not only damages the oil but also impairs the insulation system, reducing its effectiveness over time. Moisture Ingress Moisture entering through microcracks or seal failures significantly decreases the dielectric strength of the oil. Water molecules mix with the oil, forming emulsions that compromise the insulation and increase the risk of short circuits. Contamination and Corrosion Contaminants, including dust, metal particles, and other impurities, can enter the oil during operation. These foreign particles promote electrical discharges and accelerate insulation breakdown. At the same time, chemical corrosion occurs when decomposition products of the oil react with insulating materials, further degrading their properties. Partial Discharges

Partial discharges are localized electrical discharges that occur within the insulation system. Over time, this small-scale damage accumulates, leading to significant deterioration of the transformer insulation. Addressing these discharges early can help prevent long-term damage.

Methods for transformer oil purification

Various purification methods are used to assess the condition of transformer oil and ensure its restoration while in service. Mechanical Filtration This involves the removal of water, dust, and particulate matter through filters or centrifugation. Chemical purification Chemical methods use reagents like sulfuric acid or caustic soda to remove contaminants, including asphaltenes, acids, and resins. Sulfuric acid targets oxidation byproducts, while alkalis neutralize acidic compounds. However, these methods often require post-treatment to remove residual chemicals, ensuring that the oil complies with operational standards. Combined Techniques In practice, no single method is sufficient to ensure complete oil purification. Therefore, different methods are often combined. For example: Filtration is frequently used together with other purification techniques. Vacuum drying removes moisture through controlled evaporation. Vacuum spray dehydration enhances water removal efficiency.

FLD D transformer oil purification plants

The FLD D transformer oil purification plants  are an advanced solution for maintaining the high quality of transformer oil. The purification process occurs in several stages to efficiently remove undesirable impurities and moisture. Before treatment, the oil is heated to optimize the efficiency of subsequent processes. Initially, the oil containing mechanical impurities of various sizes is directed to coarse filters, which remove larger contaminating particles. At the next stage, thermal vacuum processing with removal of moisture and gas bubbles is carried out to improve the insulating properties of oil. The final stage involves fine filters that remove smaller impurities, further improving the cleanliness of oil. The FLD D series of Fluidex transformer oil purification plants offers a wide range of equipment with capacities from 5 to 53 gpm, making it suitable for various customer requirements.