Oil analysis is useful for monitoring the condition of oil-lubricated engines, turbines, and other equipment. The same goes for transformer oils used to insulate these and other electrical distribution equipment.

Insulating oil analysis provides information about the liquid, but also allows the detection of possible problems, such as electric arc, deterioration of the insulating paper and other latent failures. In addition to this, this test is part of an electrical maintenance program that aims to reduce costs.

diagnostic tool

Transformer oil analysis provides a very accurate picture of the internal condition of a transformer. Data offered by diagnostic tests include:

  • Abnormal electrical or thermal activity.
  • Effects of deterioration (condition of the insulating paper, the main indicator of a potential failure).
  • Condition of the transformer and what stage of its life cycle it is in.
  • Planning of maintenance, renovation or replacement involving the least possible expense.

Benefits of Transformer Oil Analysis

  • Assess the internal condition of the equipment.
  • Calculate the probability of a failure and the end of its useful life.
  • Identifies degradation before a failure occurs.
  • Reinforce maintenance strategies.
  • Cost savings and an excellent return on investment.

Tests that make up the analysis

Some problems can be identified by measuring the physical and chemical properties of the oil. The following tests are common during a transformer oil analysis:

moisture content

One of the most important functions of transformer oil is to provide electrical insulation. Any increase in humidity can negatively impact this property, which can result in dielectric failure. This is particularly important with fluctuating temperatures, as as the transformer cools, dissolved water will be released, resulting in poor insulation and fluid degradation. In addition to this, many transformers contain used paper for insulation, a function that can be affected due to excess moisture.

acid number

As with industrial oils, transformer oils oxidize under the influence of excessive temperature and oxygen, especially in the presence of small metallic particles that act as catalysts, resulting in an increase in acid number (due to the formation of carboxylic acids). Further reaction can generate sludge and varnish deposits. In the worst case, the oil channels become blocked and the transformer cannot cool down properly, exacerbating liquid degradation. As if that were not enough, an increase in acidity has a damaging effect on the paper.

The degradation of the oil also produces other substances, such as acids and hydroperoxides, which tend to reduce its insulating properties. Finally, an increase in acid number usually goes hand in hand with a decrease in dielectric strength and an increase in humidity.

dielectric strength

The dielectric strength of a transformer is defined as the maximum voltage that can be applied across the fluid without electrical breakdown. Because transformer oil is designed to provide insulation under high electrical fields, any significant reduction in dielectric strength may indicate that the oil is no longer capable of performing its function. Some of the things that can result in a reduction in dielectric strength include polar contaminants, substances generated from oil degradation, and paper breakdown.

power factor

The power factor of the insulating oil is the ratio between the real power and the apparent power. In a transformer, a high-power factor is a sign of significant power loss in the oil, which is often associated with polar contaminants, such as oxidized oil and water, and paper degradation.

Dissolved Gas Analysis

This test is used to determine the concentrations of certain gases in the oil, such as nitrogen, oxygen, carbon monoxide, hydrogen, methane, ethane, ethylene, and acetylene. The concentration and relative proportions of these gases can mean operational problems with the transformer. These may be associated with physical and chemical changes in the insulating oil.

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