The insulating fluid that has the greatest use in electrical equipment is mineral oil. The primary function of insulating oil is to provide a dielectric medium that acts as insulation surrounding various energized conductors. Presenting of moisture in insulation oil affect the formation of rust and consequent contamination of the equipment and taking off from maintenance, therefore it is very seriuos detail. Moisture has an effect on solid insulation aging. Moisture content of solid insulation is a persistent concern for electrical equipment as it entails several detrimental effects on the insulation deterioration. Traditionally, the dryness of equipment in service has been assessed by periodic measurements of the water content in the insulating oil. Determination of moisture content in solid insulation is rightfully an essential part of any comprehensive condition assessment management.