Everything to know about Transformer Oil Filtration

Author: Aaron Chen  Date Posted:3 February 2020 

Transformers play an important role in the electrical power industry. Transformers convert power to appropriate levels for other system components to safely use. Transformers need to be maintained to guarantee long life. Moreover, a good quality and clean oil is essential for the transformer to provide efficient performance.

Transformer oil tends to degrade over time. The oil is exposed to undesirable materials like acids, metal dust, moisture etc. When transformers contain dissolved gases, dust, and other contaminants, it is time to take action for the oil to be filtered and purified.

Transformer maintenance and services centres maintain high quality equipment for treating oil using in line transformer oil filtration techniques. These techniques help sustain an excellent performance, safety and ease of operation for transformer maintenance staff.

To know more about transformer oil filtration, here are the things that you should know.

Transformer oil and its functions

Transformer/insulating oil is often stable at high temperatures. Other than that, the following are functions of insulating oil:

  • As cooler

When voltage goes up/down, the temperature of the transformer’s windings increases, oil is used to cool down the condition.

  • As insulator

It acts as an insulator between the windings. It increases the resistance between them and avoids short circuit.

  • For security

It operates the level of oil inside the transformer. The temperature display of oil describes the inner condition of transformer and shows any short circuit status. In this way, you will prevent the transformer from being severe losses and damages.

Types of Insulating oil

  • Paraffin based – derived from special crudes that contain substantial amount of n-paraffin. This type of insulating oil is less oxidised than naphtha based.
  • Naphtha based – derived from special crudes that contain low amount of n-paraffin.

During the usage of insulating oil, it may be exposed to materials which can affect its quality. It fails to function due to factors such as excessive high temperature, oxidation and many more.

Consequently, the oil darkens in colour and the acid in it begins to increase. Oil impurities are one of the major causes of transformers deterioration.

To avoid transformer failure, your insulating oil should be free from any contamination, dirt and moisture. Thus, transformer oil filtration process is needed.

In this procedure, insulating oil is tested and treated so that transformers will function efficiently.

Dealing with transformer oil purification

To treat and purify insulating oil, transformer oil filtration process is required. Insulating oil filtration is a process of removing sludge and moisture from the transformer oil.

Benefits of transformer oil filtration

  • Insulation properties of the oil is improved
  • Longer life span of transformers
  • Lessens transformer’s breakdown
  • Good returns on investment for having a quality machine

Once the insulating oil fails to undergo this process, it can lead to:

  • Arcing – formation of an electric arc which causes breakdown of the system
  • Overheating – oil overheating
  • Corona discharges – electrical discharge caused by the ionisation of fluid
  • Insulating strength of the transformer oil will decrease

These properties are to be tested to determine the qualities of the insulating oil:

  • Dielectric Strength or Breakdown Voltage (BDV)
  • Water Content
  • Neutralisation Value
  • Interfacial Tension
  • Colour and appearance
  • Test for Oxidation Stability
  • Specific Resistance (Resistivity)
  • Flash Point
  • Pour Point
  • Viscosity
  • Sludge Test
  • Dissolved Gas Analysis (DGA)

To further understand how the transformer oil is tested, below is the process.

Insulating oil filtration process

  1. Rising oil temperature

First step is to raise oil temperature up to 65°C to give latent heat which separates moisture and gases. Heating the oil will make it easier to filter because of the decrease in oil viscosity.

  1. Removal of dirt and impurities

Second step is to remove sludge and dirt from the insulating oil. There are 2 ways to eliminate dirt in the transformer oil.

  • By filter candles

Insulating oil filtration by filter candles can be classified by using classical edge filter or depth type filter. However, new advancements were made in which transformer oil filtration machines use filter cartridges instead of edge type paper filters.

  • By centrifuging action

Another method for separating dirt from oil is through centrifuging. With this process, you can save recurring cost of changing filters.

  1. Dehydration and degasification of insulating oil

This is the stage of dehumidification of insulating oil and removal of gasses. This process is completed in the degassing chamber.

Transformer oil deterioration should be minimised

Research shows that 80% of oil related failures and breakdowns are caused by contaminated oil. Preventive oil maintenance is therefore an important factor to ensure optimum equipment reliability.

A successful insulating oil filtration procedure can be achieved by using a reliable transformer oil filtration equipment. This will extend the effectiveness and reliability of your transformer.

Find a good transformer oil filtration machine

Transformer oil filtration is a great help to any businesses. Thus, a good transformer oil filtration equipment is needed. There are many companies that offer different kinds of equipment. However, choose a vendor that manufactures high quality insulation oil purification machine that can ensure high Return on Investment (ROI).


Maintaining your transformer oil is necessary so that your transformers can function effectively. It doesn’t just help prolong your equipment’s life span, but also improve its efficiency.

You could use a reliable Transformer Oil Filtration Equipment for Insulating Oil Treatment (IOT). This will help you maintain your equipment in the long run.

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