Analyses of transformer dielectric oils are necessary and must be carried out periodically in order to prevent possible incidents, the consequences of which are often very serious for the operation of transformers.

These analyses essentially make it possible to

Identify thermal/electrical faults in the transformer
Check the state of the transformer insulation
Check the state of ageing of the dielectric oil
Check the condition of the cellulose insulators

The benefits of oil analysis :

Reduction of transformer damage
Preventive removal of transformers prevents damage and unscheduled outages
Avoidance of expensive operating costs and investments due to major damage.
Optimisation of maintenance programmes.

Definitions of the most important oil analyses:

Water content

Moisture, which is present in large quantities in the oil, is an element that significantly degrades the insulation in transformers.

Acidity index

By measuring the acidic constituents of oils, the acid number of a dielectric oil is defined. Acids have an impact on the degradation of cellulosic materials and can also be responsible for the corrosion of metal parts of a transformer. The acid number is an indicator of the state of ageing of a transformer oil.

Delta tangent

The dissipation factor or power factor which is a dimensionless quantity is directly related to the AC resistivity and permittivity of a dielectric fluid.

Dielectric strength

The breakdown voltage defines the ability of a dielectric oil to withstand electrical stress.

Dissolved gas analysis

The main gases that are monitored in an operating transformer are:

H2 (hydrogen),
O2 (oxygen),
N2 (nitrogen),
CH4 (methane),
CO (carbon monoxide),
CO2 (carbon dioxide),
C2H4 (ethylene),
C2H6 (ethane),
C2H2 (acetylene).

The presence of these gases is the result of various electrical faults inside power transformers.

Furan content

Furan compounds are produced when the insulating properties of paper degrade; measuring the concentration of these compounds gives an indication of the condition of the paper-based insulation.

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