Why does new transformer oil need to be filtered?

Although new transformer oil meets standard specifications upon leaving the factory, filtering it before it's put into operation is a crucial and essential process. This isn't because the new oil is "substandard," but rather because it requires the utmost protection for the transformer, a core piece of electrical equipment. The main reasons for this can be understood from the following perspectives:

1. Removing contaminants introduced during manufacturing, storage, and transportation

Even the highest-quality new oil inevitably introduces trace amounts of contaminants during filling, storage, transportation, and injection into the transformer. These contaminants primarily include:

Solid particles: such as metal shavings, dust, and fibers. These can originate from sources such as the inner wall of the oil drum, pipelines, and pumps and valves.

Moisture: Moisture in the air can enter the oil drum through respiration or condense into water due to temperature fluctuations.

Gases: Air can dissolve or mix into the oil.

These contaminants are a hidden danger that must be eliminated for the extremely demanding internal environment of the transformer.

2. Ensuring and Improving Insulation Performance (The Core Reason)

The core function of transformer oil is to serve as an insulating medium, isolating high-voltage live components from grounded components.

Moisture is the natural enemy of insulation: even trace amounts can dramatically reduce the oil's dielectric strength (i.e., breakdown voltage). Filtration systems (especially vacuum oil filters) can efficiently remove free and dissolved water, reducing the oil's moisture content to extremely low levels (e.g., below 10 ppm), ensuring that its insulation performance meets the highest standards (typically >60 kV or even higher).

Particles cause electric field distortion: Tiny conductive particles form "bridges" in strong electric fields, creating conductive pathways that can cause partial discharge and even insulation breakdown. Precision filtration removes these tiny particles, ensuring a uniform distribution of the electric field.

3. Ensuring Long-Term Reliable Operation and Equipment Life

Preventing Insulation Material Aging: The solid insulation materials in transformers are primarily insulating paper and cardboard. Moisture and impurities accelerate the hydrolysis and aging of these cellulose materials, causing them to lose mechanical strength and insulation properties. Using pure oil maximizes the life of solid insulation, thereby extending the life of the entire transformer.

Inhibiting oil oxidation: Metal particles (especially copper and iron) act as catalysts for oil oxidation reactions, accelerating oil degradation and producing acid and sludge. Sludge deposits on the windings and core impair heat dissipation and corrode solid insulation. Filtering out these catalysts delays oil oxidation and maintains long-term oil quality stability.

4. Removing Dissolved Gases

New oil may contain dissolved air (oxygen and nitrogen). Vacuum oil filtration not only removes water but also degases it.

Oxygen: The primary cause of oil and solid insulation oxidation. Removing oxygen effectively slows aging.

Although inert, nitrogen removal provides a clean background for online monitoring (DGA) of fault-signaling gases (such as acetylene and hydrogen) generated during transformer operation, improving monitoring accuracy and sensitivity.

Summary

Thus, filtering new transformer oil is essentially a process of continuous improvement and risk management. It ensures the oil injected into the equipment is in an unprecedentedly pure state, achieving:

Extremely high dielectric strength to withstand high-voltage shocks;

Extremely low water content to protect the solid insulation and delay aging;

Extremely low impurity content to prevent electric field distortion and catalytic oxidation.

This process directly impacts the safe operation, long-term stability, and service life of the transformer after commissioning, and is a crucial technical specification and safety measure in the power industry. For critical power equipment valued at millions or even tens of millions, this upfront investment may be negligible, but the safety and long-term economic benefits it brings are enormous.