Tests and Trials: Sport, Art or Industry? Analysis of Transformer Oil Purification

The correct use of oil guarantees the reliability of industrial equipment and the prevention of equipment failures.  Transformer oil is a dielectric insulator and a coolant.  It also serves as an arc extinguisher preventing shorts and internal fires.

Transformer oil parameters degrade over time as the oil ages.  Oil oxidation is mostly caused by external elements such as water, air, acids and heat.  Aging of oil is best indicated by its acidity level, water content, and sediment and sludge formation.

Sludge accumulates in the solid insulation, the core, in cooling channels and other places inside the transformer.  Sludge is a dangerous enemy that degrades the oil’s cooling and heat transfer capabilities and damages the solid insulation causing it to disintegrate.  A short-circuit in the transformer windings becomes a much higher possibility due to oil degradation and sludge build up.

The acid level of the oil, as measured by the “Acid Number is the main indication of oil degradation and oil aging.  Acidity is measured by special litmus paper that changes color when subjected to contaminants.  Acids can damage cellulose insulation and metal parts of the transformer.  Acid levels can also measured through an oil analysis program.

The Acid number, as the main indication of transformer oil quality, is the amount of grams of KOH required to neutralize all free acids in one gram of oil.  The Acid number indicates how much the oil has aged and whether it should be regenerated using the GlobeCore Process.  Once the Acid number reaches 0.08 and higher, the transformer oil becomes aggressive and begins to destroy the solid insulation of the transformer.  The Acid number therefore, is the best indicator of when to service your transformer before irreversible damage is done to the insulating paper.

Besides chemical parameters, transformer oil must comply with certain physical and electric parameters.  Degradation of these important oil qualities may indicate problems inside your power equipment.

For instance, the oil’s flashpoint must be high enough to ensure fire safety in overload conditions and high temperature increases inside the transformer.

Dielectric strength of transformer oil is important for the prevention of breakthroughs in the transformer insulation.  This parameter is measured regularly by high voltage breakthrough indicators.  Transformer oil is tested six times with 10 minute intervals between each test.  The average of six tests is used to determine the dielectric strength.  If the results are unsatisfactory, another sample is tested and a decision on the course of action is made.

Fresh or used transformer oil must be tested before being placed into the transformer.  Some parameters tested are particulate matter content, general oxidation stability, transparency, dissipation factor, flash and setting points, viscosity, acidity and water content.

These measures are designed to identify and resolve problems before the they can cause a transformer failure shutting down the transformer.

Transformer oil is purified of contaminants, acids and gases in purification and regeneration equipment specifically designed for transformer maintenance.  Complete preventive maintenance systems, such as the GlobeCore CMM-R line of equipment will reduce costs and downtime while increasing operating profits.


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