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Supervision and maintenance of liquid insulated electrical equipment ensuring compliance to Electricity at Work Act, British Standards and insurance requirements

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Eden Transformer Oil is a family owned and operated company that has over a quarter of a century’s experience in the inspection, analysis and maintenance of liquid insulated electrical equipment to British standards.

Working with your site engineers and facilities managers our inspection, sampling and maintenance services will ensure your equipment is inspected and maintained to the appropriate standards and therefore meets insurance, safety and environmental regulations


Why maintain insulating liquid?

The oil in electrical equipment provides three key functions:-

• Cooling – Be it forced or natural circulation, the liquid carries heat away from the core to the cooling fins or outer case.  Preventing equipment from overheating is an important aspect of equipment maintenance to ensure the longest possible working life of the equipment.

Laboratory research found that an increase of just 8 oC halves the working life of a transformer

• insulation – Impregnated in solid insulation and circulating freely within the equipment the liquid plays the vital role of providing electrical protection and, in the case of switchgear, extinguishing arcs. Moisture and particles have a negative impact on the insulation properties of the liquid.

• Information – Data from internal events such as partial discharges, heating and cellulose degradation are all stored in the oil for professional analysis and interpretation.


A well planned testing and maintenance programme is more cost effective than the replacement of oil and any equipment failures.There are three main classes of insulation liquid governed by three British Standards – mineral oil BS EN 60422:2013, synthetic oil BS EN 61203:1995, silicone oil BS EN 7713:1993.

What if the liquid fails to meet specification?

At this stage many engineers and sub-contractors simply default in to replacing expensive insulating liquid. This is both technically unnecessary  and financially punitive. Using mineral oil as an example, the British standard for moisture in category C distribution equipment (<72.5kV) is 20mg/Kg, whereas the specification of a drum of new oil is up to 40mg/Kg.

The British standard for new oil actually states “Before filling the electrical equipment, the oil should be treated to meet the requirements of IEC 60422” (BS EN 60422:2013).


Image 1 and 2 moisture content

The treatment referred to is vacuum dehydration, also known as purification, but this can be applied to existing oil not just new oil. The process of dehydrating oil in situ also helps dry the transformer core for a total service, not just the oil.

Financially, applying vacuum dehydration is a more cost effective solution and in many cases can be carried out whilst the transformer is still energised thereby eliminating expensive loss of productivity.

The chart to the right provides a comparison based upon a typical transformer containing 1,000 litres of mineral oil that is replaced and the waste oil removed to an Environment Agency approved processing facility.

The cost of replacement oil includes: new oil, flushing oil, empty drums for waste, disposal of waste and labour of £500. The cost of Vacuum Dehydration-Filtration includes, all labour, plant and consumables. 




Sample and inspection

On-site sample and inspection services:-

Draw samples for on or off site analysis.

Inspect desiccant breathers and replace if required.

Visually inspect transformer for leaks.

Check and top-up insulating liquid levels.


On-site transformer oil purification

Using our mobile vacuum dehydration-filtration plant we can restore the insulating liquid to specification:-

Mineral Oil


Xiameter Silicone Transformer Liquid


Polychlorinated Biphenyls (PCB) services

Our PCB products and services include:-



Labels and Signage


Oil analysis

The following service are available on our ‘analysis by post’ service or by Eden staff attending site to draw the samples.

Mineral oil to BS EN 60422:2013

MIDEL 7131 insulating fluid to BS EN61203:1995

Silicone insulating liquid to BS7713:1993

Dielectric strength BS EN 60156:1996

Water content BS EN 60814:1998

Acidity BS 2000-1:1995

Dissolved gas analysis (DGA) BS EN 60567:2005

Furans analysis BS EN 61198:1994

Polychlorinated Biphenyl (PCB) analysis to BS EN 61619:1997


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