Do you know want to know what is Transformer Oil Purification ?  how to do transformer oil filtration? Or what is oil purification process?.

In this article you will understand transformer oil purification process , steps and methods involved in oil purification process.

Transformer oil filtration machine

Transformer oil purification is a process to remove sludge, dissolved moisture and dissolved gases from the oil.

Before we move to process details, Lets see why transformers need purified oil  ?

Need for transformer oil filtration

As discussed in details Advantages of transformer oil filter  in post why transformer oil filtration is required? here we will see in brief advantages for transformer oil purification :

  • Improved insulation properties of the oil and hence the other media like paper/cellulose insulation
  • Better the insulation of transformer, longer the life of the transformer and lesser the breakdown of the transformer
  • Longer the life of the transformer asset, good returns on investment of the asset
  • Lesser breakdowns and failure of the transformer results in uninterrupted power supply

For good performance of transformers we require filtration machines designed and manufactured with standards. At NACH we manufacture Oil purification machines with Standard (BIS, NEMA, IEEE, IEE, ASTM, ASME, IEC) for good performance of transformer.

Now lets move to, Transformer Oil Purification Procedure

Transformer Oil Purification Procedure

Transformer is one of the main asset in the electrical power industry which needs to be maintained for guaranteed uninterrupted power transmission in order to get assured revenue benefits.

Transformer life mainly depends on the quality of oil volume it contains.

Regular transformer oil filtration assures long and consistent results from the transformer.

Transformer oil purification is a process to remove sludge, dissolved moisture and dissolved gases from the oil. Transformer oil conditioning may also include to some extent improving the acidity of the oil.

A good oil purification system is able to deliver filtered oil with parameters as per the standard specification.

However, this revival of the oil by oil filtration plant to standard oil parameters is based on the quality of unprocessed oil and its initial process. In case the unprocessed oil does not match the standard oil parameters, then the effort of transformer oil filtration is all in vain. Alternate method of regeneration of transformer oil should be adopted in this case.

Here we shall look at the method of the transformer oil filtration by vacuum type dehydration and centrifuge type removal of solids and water separation.

Transformer oil conditioning is a stream line oil filtration process of sludge purification, moisture removal and gas removal.

First step in the transformer oil purification

The first step in this serial process is to raise the oil temperature to a desired level, generally upto 65 Deg C. This aids to give the oil latent heat which later aids to dissociate the moisture and gases from oil in the degassing chamber. Additionally the viscosity of the oil drops which aids in better filtration to some extent. Recommended heater design should consider an area of heating of about 1 to 2 W/ In the transformer oil purification plant, the heating system is protected against over pressure built up and excess temperature rise.

Second step of transformer oil purification

The second step of transformer oil purification plant is removal of sludge and dirt from the transformer oil.

Two methods have been used for removal of the sludge:

  • Removal of sludge by filter candles. and/or
  • Removal of sludge by centrifuging action.

Removal of sludge by filter candles.

Transformer oil filtration using filter candles in the transformer oil purifier machine can further be classified as:

  • Filtration using the classical edge filter
  • Filtration of transformer oil using the depth type filter.

Both methods of cartridge type filtration are prevalent and owe certain advantages and disadvantages.

The edge type filter system can be cleaned and be reused for at least three to four times, however, cleaning and fitting of the edge filters involves considerable time and human effort. This system is robust to handle large quantity of sludge. Edge filters can be cleaned by reverse pressurized dry air/nitrogen flow in order to remove the contamination. After de-sludging the paper stack is removed and dried in oven/ bright sunlight and reused. This operation demands experience and skill set.

New trends and technology in the market have driven transformer oil filter machines to use filter cartridges instead edge type paper stacked filters. These cartridges are similar to those of the water filter cartridges and can be selected from a variety of purification range say from 500 micron to 0.5 micron size.

The advantage using these cartridges over the edge filter is

  • No moisture storage, since the filter media used can be non-hygroscopic
  • Easy to replace with less human effort and easy availability.
Removal of sludge by centrifuging action.

An alternate method used for dirt separation from oil is centrifuge. Routine transformer oil filtration or transformer oil conditioning is often confused with transformer oil centrifuging. Transformer oil centrifuging is all together a different technology and has a little impact on improving the oil parameters. Centrifuges used for separation of dirt from the transformer oil can be slow speed type centrifuges that do not require additional electric motor to spin the centrifuge cone at high speed.

However, the dirt separation from oil with such centrifuging has limitations since these centrifuges cannot remove the dirt less than 10 micron level. Thus a power driven centrifuge becomes evitable which scales up the cost of the oil conditioning machine.

Only advantage of the centrifuges is that the recurring cost of changing filter elements is saved. Power driven centrifuges can remove water from the oil that is in free form but not the dissolved moisture. Manufacturers of power driven centrifuge also often do not guarantee removal of moisture to a level less than 5 ppm.

Third  step in the oil filter machine

The third step in the oil filter machine is dehydration of transformer oil and degasification of the transformer oil.

Dehydration  and Degasification of transformer oil

These processes of dehumidification of transformer oil and removal of gasses is executed in the degassing chamber. The dissolved water oil separation or dissolved gas oil separation is possible at reduced pressure, i.e. vacuum, due to difference of boiling point of water, gas and transformer oil. In the process of separation of gases from the oil it becomes important to retain the aromatic hydrocarbons so that the original properties of the oil are retained. When the water level in the oil is above saturation level of the transformer oil, oil is observed in free water. Removal of free water can be done by power driven centrifuge or by coalescing principle, where the later is more effective and economical in practice.

Why NACH make oil filter plants

With the different processes involved in the transformer dehydration and degasification plant it is evident that the processes should be neatly designed to tame different oil volumes to be filtered. With increasing power demands and scaled up voltages transformer oil filtration is becoming more and more demanding and sophisticated. With the advent of new technology now the water activity or the water content in the transformer oil is measurable online and methods of laboratory testing like the titration method are becoming limited. At NACH we are update with the recent trends and technology pertaining to the oil filtration and also with requirements imposed for UHV and EHV grade transformer oils.

At NACH we understand the requirements of the oil filtration and are committed for resulting a good transformer performance.  Feel free to contact us,  we shall be happy to help you  and provide you a quick response.

Categories: machinery


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