Chemical Parameters of Transformer Oil
(1) Water Content in Transformer Oil
Moisture or water content in transformer oil is highly undesirable as it affects adversely the dielectric properties of oil. The water content in oil also affects the paper insulation of the core and winding of transformer. Paper is highly hygroscopic in nature. Paper absorbs maximum amount of water from oil which affects paper insulation property as well as reduced its life. But in loaded transformer, oil becomes hotter, hence the solubility of water in oil increases as a result the paper releases water and increase the water content in transformer oil. Thus the temperature of the oil at the time of taking sample for test is very important. During oxidation acid are formed in the oil the acids give rise the solubility of water in the oil. Acid coupled with water further decompose the oil forming more acid and water. This rate of degradation of oil increases. The water content in oil is measured as pm(parts per million unit).
Water content in oil is allowed up to 50 ppm as recommended by IS–335(1993). The accurate measurement of water content at such low levels requires very sophisticated instrument like Coulometric Karl Fisher Titrator.
(2) Acidity of Transformer Oil
Acidity of transformer oil, is harmful property. If oil becomes acidic, water content in the oil becomes more soluble to the the oil. Acidity of oil deteriorates the insulation property of paper insulation of winding. Acidity accelerates thee oxidation process in the oil. Acid also includes rusting of iron in presence of moisture. The acidity of transformer oil is measure of its acidic constituents of contaminants. Acidity of oil is express in mg of KOH required to neutralize the acid present in a gram of oil. This is also known as neutralization number.
