Why Maintain Transformer OIl

Putting aside the electric strength of the transformer oil or insulating liquid in a transformer, it is important that the liquid is maintained so that the integrity of the core transformer components are retained. Key to this is the paper insulation and cellulose. The combination of heat, moisture and oxidisation has a detrimental effect on the paper and it’s mechanical strength.

Maintaining the mechanical strength of the paper is the key to extending the lifespan of a transformer. The rising commodity prices of the metals and materials used in building or restoring a transformer, and the cost of installation make the proper maintenance, and extension of the working life, of the transformer all the more important.

Research by Stanley Myers, Joseph Kelly and Robert Parrish for their book A Guide To Transformer Maintenance (ISBN-13 978-0939320004) demonstrated that the working life of the insulation paper is halved by the doubling of moisture, but more surprisingly an increase of just 8 degrees centigrade also halves the working life.

During the normal operation of the transformer, along with the expansion and contraction caused by the power load, moisture and contaminants resulting from oxidisation will build up in the oil and are transferred to the paper. These contaminants have the detrimental effect on the core.

Treating the transformer oil, or insulating liquid, cannot reverse the damage to the insulation paper and cellulose, but it can significantly reduce the aging process, thereby extending the lifespan of the transformer.

As is so often is the case, a well planned testing and maintenance programme is more cost effective than the replacement of oil and any equipment failures.

In the following pages we demonstrate the financial and technical advantages of on-site treatment.

Purification Vs Replacement of Oil


 New Oil, BS EN 60296:2012Specification after passing through Eden's plant
Dielectric Strength 30 kV 60 kV
Moisture Content 40 mg/Kg <10 mg/Kg

  • The question we are always asked is, that so long as the British Standards have been met, isn't that enough? The answer is that the minimum specification will be an improvement in the current insulating medium but the drier the oil the more moisture is transferred from the insulation paper and therefore extends the life of the oil and electrical equipment.

    The British Standards applicable to new insulating liquids are:-

    • New Mineral Oil : BS EN 60296:2012
    • New MIDEL: BS EN 61099:2010
    • New silicone insulating liquid : BS EN 60836:2005

  • Typically, Eden can deploy a mobile treatment plant to restore the insulating oil for less than half of the total cost of replacement. The cost differential for MIDEL7131 or Silicon liquid is even greater.

    The additional benefit of purification is that it also works at its most effective whilst the transformer is energised and this also brings the benefit that there is no loss of productivity to the equipment that is fed by the transformer.

  • It is important not to overlook the environmental benefits of purifying the oil. As no new virgin products are used there is an instant benefit to the environment even before considerations such as the impact of international transportation and refinement are taken into account. And, with no oil being replaced, there is no hazardous waste oil to transport.

    Purifying the oil or other insulating medium in a transformer is probably one of the few environmentally beneficial alternatives that is also cost and productivity effective at point of delivery and over the lifespan of the equipment.

    Purification should be the first option to consider in any transformer maintenance programme.

Mobile Purification Plant

Eden has been
treating transformer
oil on-site since 1985.

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Testing Service

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site or off site service at
your convenience.

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