Oil Processing

Transformer oil processing is necessary for the safe operation of instrument transformers, power transformers, reactor equipment, and oil circuit breakers. During transformer operation, the oil undergoes significant changes, a process commonly referred to as aging. These changes affect the chemical and electrical properties of the oil that maintain its functionality. Aging reduces dielectric strength, leads to the accumulation of deposits on transformer components, impairs heat dissipation, accelerates the aging of cellulose insulation, and deteriorates its electrical insulating properties.

Characteristics of Usable Transformer Oil

In order to ensure reliable performance, transformer oil shall meet the following criteria:

• Acid number: not more than 0.05 mg KOH per 2.2 lbs of oil.
• Water extract reaction: neutral.
• Mechanical impurities: free of visible contaminants.
• Flash point reduction: not more than 9 °F compared to the initial value.
• Suspended carbon: absent in transformer oil; minimum content in circuit breakers.
• Dielectric strength: not less than 500 V/mil for transformers up to 10 kV.
• Density at 68 °F: 0.030–0.032 lb/in³.
• Specific volume resistivity: 10¹⁴–10¹⁵ Ω·in at 68 °F.
• Dielectric dissipation factor (tan δ): not more than 2 % at 68 °F, 7 % at 158 °F.
• Ash content: not more than 0.005 %.

Oil Processing

Over time, exposure to heat, water, and air leads to the deterioration of oil properties. In order to maintain continuous and safe transformer operations, oil should be either replaced or restored. Oil processing is often the preferred choice as it ensures conservation of natural resources, making it both environmentally sustainable and economically advantageous.

Methods of Oil Processing

There is a variety of oil restoration methods categorized into physical, physicochemical, and chemical processes.

Physical Methods

Physical processes remove solid impurities, small amounts of water, and certain resins or coke-like substances.

1. Settling: allows impurities to separate from the oil over time. While simple, this method is time-consuming and ineffective for smaller particles.
2. Centrifugation: separates the oil into fractions — solids, oil, and water — using centrifugal force.

Physicochemical Methods

These methods are more advanced and include:

• Coagulation: involves using a coagulant to combine smaller particles into larger ones, which are then removed physically, often through filtration.
• Selective Purification: targets specific impurities that most adversely affect oil performance.
• Adsorption: uses adsorbents to attract and capture contaminants. However, the need for considerable quantities of adsorbents and their subsequent disposal may be disadvantageous.  

Chemical Methods

Chemical processes include:

1. Sulfuric Acid Purification: removes contaminants with the use of concentrated sulfuric acid, but forms acidic sludge as waste, which is challenging to dispose of. Furthermore, it cannot remove all impurities.
2. Hydrotreatment: involves passing hydrogen through the oil under high pressure and temperature. While effective and safe, this method involves substantial costs.

FLD Oil Processing Units

In order to address the challenges of transformer oil aging, Fluidex offers advanced solutions with its FLD D and FLD R units.

• FLD D Units: these systems are designed for degassing, mechanical impurities removal, and heating of transformer oil. They are compatible with transformers up to 1,150 kV and also ensure heating of oil-filled equipment and vacuuming of transformers. The FLD D units increase the breakdown voltage of oil to 70 kV and heat the oil to 194 °F.
• FLD R Units: these systems extend transformer service life by restoring the dielectric strength and chemical properties of insulating oils. The FLD R units remove decomposition products and acidic constituents, clarify the oil while enhancing oxidation resistance and gas absorption capacity. This on-site regeneration process dissolves deposits from transformer winding insulation, which are then removed using sorbents.

Notably, the FLD R units use Fuller’s Earth, a sorbent that can be reactivated and enables continuous oil processing without interruptions for sorbent replacement, maximizing efficiency and minimizing waste.