Electric oil condition

Electric oil

electric oil in electrical distribution equipment
Electric oil provides an insulating effect in electrical equipment.

The maintenance of transformers has evolved over the past years from a necessary expenditure item to a strategic tool in the management of electrical transmission and distribution networks. Extreme reliability of electrical power distribution is required. Although the failure risk of a transformer and other equipment filled with electric oil is small. They inevitably lead to high repair costs, long downtime and possible safety risks. In addition, transformers are too expensive to replace regularly and must be well maintained to maximize their life expectancy.

It is known that regular oil analysis is useful in monitoring the condition of engines, turbines and other oil-lubricated equipment. The same can be said for transformer oils that are used to isolate transformers and other electrical distribution equipment. The analysis of insulating oils provides information about the oil, but also allows the detection of other problems, including contact arcing, aging insulating paper and other possible failures. It is an indispensable part of a cost-efficient maintenance program for electricity.

Ensuring the reliability of transformers

By accurately monitoring the condition of the electric oil, sudden errors can be detected in time and unexpected failures can be prevented. Furthermore, an efficient approach to maintenance can be applied and the optimal intervals are determined for replacement. By measuring the chemical properties of oil, a number of problem conditions can be determined which are related to the oil or the transformer.

Moisture content

One of the most important functions of a transformer oil is the supply of electrical insulation. Any increase in moisture content can reduce the insulating properties of the oil, which can result in dielectric breakdown. This is particularly important in fluctuating temperatures because, as the transformer cools, the dissolved water will be released, resulting in poor insulation and moisture degradation. In addition, many transformers contain cellulose-based paper that is used as insulation in the windings. Again, too high a moisture content can result in the breakdown of this paper insulation resulting in a loss of performance.


Like industrial oils, transformer oils are oxidized under the influence of excessive temperature changes and oxygen. The presence of small metal particles that act as catalysts will result in an increase in the acid number. Further reaction can lead to sludge and varnish deposits. This can lead to clogging of the oil channels, as a result of which the transformer is not cooled properly. This will further aggravate the degradation of the insulation oil. The increase in acidity has a harmful effect on the cellulose paper.

Degradation of electric oil also produces by-products such as acids and hydroperoxides. These tend to degrade the insulating properties of the oil. An increase in the acid number often goes hand in hand with a decrease in dielectric strength and increased moisture content.

Insulating effect

The dielectric strength (ASTM D300-00) of transformer oil is defined as the maximum voltage applied across the liquid without electrical interference. A reduction in dielectric strength may indicate that the electric oil is no longer able to perform this vital function. Causes that can result in a reduction in dielectric strength are polar contaminants, such as water, products of the degradation of oil and cellulose paper.

Condition monitoring

With real-time monitoring of electrical insulation oil, any change in physical or chemical properties caused by the concentration of gases can be signaled. This can play a crucial role in preventing unscheduled outages of electrical transmission and distribution equipment. This applies to all critical oil-filled electrical equipment, transformers, circuit breakers and voltage regulators.

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