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Maintenance & service on transformers up to 500 KV

Oil sampling

During sampling and transport of the oil sample, great care must be taken to ensure that the test results provide a representative assessment of the transformer. 1 litre of oil is required for an oil test; suitable oil sample bottles can be requested from us. A separate 1 litre oil sample is required for a gas analytical oil test. Sampling point for gas analytical tests: normally boiler “Top” Sampling point for other tests: normally boiler “Bottom

  • Use clean 1-liter bottles with gas-tight closures as sample containers.
  • Special aluminium bottles with plastic screw cap and seal are usually used.
  • The closure must be so tight that no air is drawn in when the sample cools.
  • If glass bottles are used, only take the oil sample if it is certain that the temperature of the sample is greater than or equal to the storage or shipping temperature when it is taken.
  • Take samples for gas analyses only by the overflow method. The operations must be carried out rapidly and without any interruption in order to prevent the oil sample coming into contact with the atmosphere as far as possible.

UVR oil regeneration plant

The UVR process is a unique and patented technology. The process is so sophisticated that practically any fuel or used mineral oil can be regenerated.The UVR process units can be adjusted or re-set to suit the requirements to process any type of fuel or waste oil, so that different regeneration systems do not have to be used for different oils.The UVR units remove sulphur, hydrogen sulphide compounds, tar and other contaminants.The oil and fuel products remain clear and stable after the regeneration process.The UVR units have successfully regenerated dielectric transformer oil, turbine oil, industrial oil, heavy oil and diesel fuel in hundreds of plants around the world.In addition, our plants use a special sorption material to combine the cost-effective and efficient recovery of oils and fuels.In many cases the regenerated product is superior to the original product in its properties.

Gas in Oil – Analysis (DGA=Dissolved Gas Analysis)

Due to the natural ageing of the oil and insulating parts, but especially under the influence of thermal or electrical faults, fission gases are formed which are dissolved in the oil.

By means of DGA mainly slowly developing defects can be detected. The temporal development of the gas concentrations enables a trend analysis, which also allows a prognosis of the transformer’s lifetime.

  • Partial discharges and discharges
  • Formation of foreign layers on contacts
  • Abnormal cellulose degradation
  • Local overheating of metal parts

Colour and appearance (according to ISO 2049)

Although colour and appearance are not relevant characteristics and are not a criterion for any action, they are useful for comparative assessment:

A rapid darkening or darker oil are indications of oil ageing.

Breakdown voltage (measured according to VDE 0370 part 5)

The breakdown voltage indicates how well an insulating oil can withstand the electrical load and is therefore decisive for the operational reliability of the transformer. The limit values for breakdown voltage depend on the series voltage or the type of device.

Water content

Water results from the ageing of the cellulose insulation materials to a small extent from the oil ageing and mainly from the diffusion of ambient moisture through poorly maintained dehumidifiers and/or a defective sealing system Even in the expansion tank moisture is produced although a dehumidifier is connected upstream, these findings have not been considered in the past. Water in the oil is in equilibrium with moisture in the solid insulation and lowers the breakdown voltage and accelerates the aging process. The exact determination of the moisture in the cellulose can only be done by sampling and subsequent Karl Fischer tritation. A modern method for determining moisture in insulation is PDC analysis.

Transformer maintenance

The most important elements of power distribution are transformers, these vary between distribution, machine, special and grid coupling transformers.

In principle, all transformers consist of the following materials:

  • Insulating materials such as pressboard
  • Paper
  • Wood and transformer oil used for insulation and cooling
  • Electrical sheets
  • Copper

These materials are subject to natural aging during normal operation, which is highly dependent on the operating conditions. In normal operation, they are approx. 25 – 30 years, provided they are professionally maintained and cared for.

However, during the course of a transformer’s life, there are events that can be regarded as non-normal operation:

  • e.g. overload, overvoltage and, due to overheating, further problems in cooling.

These events accelerate the ageing of the materials. One of the most common causes of transformer malfunction is oil. To detect this in good time, it is essential to carry out regular oil checks. With early detection, countermeasures can be taken, which certainly does not prevent the aging process, but largely delays it.


Our company uses the BORNACK-LATCHWAY stop structure for the inspection of large transformers and on construction sites.

For the purpose of maintenance, revision and repair, transformers must be planned or unexpectedly climbed. According to the relevant regulations of the professional associations, personnel must be secured against falling.

In contrast to fixed baffles, which have to be removed for the operation of the plant, BORNACK-LATCHWAY fixed stop structures are available at all times.

The LATCHWAY system consists of a horizontally tensioned stainless steel safety rope with rope guides at regular intervals of approx. 1.5 m. These guides can be passed over freely by the special running element without loosening the safety device. This increases the acceptance of the employees to use such a safety device.

A safety shock absorber with tensioning device keeps the rope at a defined pretension and protects people and material from overloading in the event of a fall accident. The intermediate guides prevent the rope from sagging too much and thus avoid the risk of impact on the relatively close ground.