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 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. 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/sq.cm. In the transformer oil purification plant, the heating system is protected against over pressure built up and excess temperature rise.
The second stage 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. Transformer oil filtration using filter candles in the transformer oil purifier machine can further be classified as filtration using the classical edge filter and 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. 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 (a) no moisture storage, since the filter media used can be non-hygroscopic (b) easy to replace with less human effort and easy availability.
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.