Miomir Kotlica - KNEES International LTD -Canada
Raka Levi - LEVICO INC. -USA
Potkonjak - KES Engineering - Canada

Insulation in power transformers working in electrical systems besides normal aging is also subject to a deterioration for different other reasons. Some of the most destructive regimes are electrical faults and overheating. Oil paper insulation is chemically complex system and ageing process is manifested in changing of oil chemical structure and reducing dielectric strength of solid insulation. These changes seriously affect normal operation of the transformer and can result in expensive damages. The basic requirement is that insulating materials must be chemically and thermally stable. During the production, transformer insulation must be maximaly dehidrated. This task is not so simple one since oil and cellulose do have different adsorption characteristics. Celullose is known as hydrophilic, and oil is hydrophobic. Total dehidration of cellulose would cause loss of mechanical and insulation properties. The stabilization of insulation oil has not been solved in satisfactory manner. This problem with insulation oil is the result of complex oxidation process in oil during regular transformer operation. The oxidation mechanism further helps the formation of lower carbonyls, carboxyls, water and gases in oil. These materials are actually products of ageing mechanism in the oil. Combining the ageing mechanisms in cellulose and oil, results in very complex mechanisms, which accelerate degradation of the oil-cellulose insullation many times. At the present, looking for the solution of this problem, there are two directions of developments: 1. Slowing the degradation process by adding additives /inhibitors. 2. Removing products of oil and cellulose degradation using an adsorption method to maintain initial quality. The utilization of new molecular adsorbents and specially formulated materials alows oil regeneration directly from transformer tank.