Transformer Insulation for Oil cooled Transformers

Oil cooled transformers form the basis and backbone of any transmission and distribution system of power in a country. Oil cooled transformers are the most preferred choice due to their relatively better efficiency and life compared to other types of transformers.

Transformer insulation used in such oil-cooled equipment is cellulosic material made from pure unbleached kraft wood pulp. These can be in different forms namely, Transformer Insulating Pressboard and Insulation paper.

Given below are different types of Transformer Insulation which are being generally used:

Pre-Compressed Press Board components

Pre-Compressed Press Board components like spacers, ducts, trapezoidal strips, T- strips, blocks, washers or circles, yoke insulation, phase barrier insulation, cylinders, ladders, etc. These are manufactured by machining of transformers insulating pre-compressed pressboards by process of shearing, punching, moulding, rolling, etc. These components are used in coils and inside of the transformer to insulate various active parts from each other and also to facilitate sufficient oil flow between components for cooling.

Transformer insulating kraft paper 

Transformer insulating kraft paper comes in thickness from 1.5 mil to 5 mil. It is used for various interlayer applications and also for the covering of aluminum and copper conductors in transformers. They are also made from long virgin fibers of cellulose having high mechanical and electrical strength. The water used for the manufacturing of this paper must be demineralized and of very high purity so that the conductivity of the paper is extremely low.

Transformer insulating pressphan paper 

Transformer insulating pressphan paper comes in thickness from 5 mil to 20 mil. This is used in both interlayer applications as well as cylinders in small transformers. The density of this paper is more than Insulating kraft paper as the pressing load is higher in this case. The breakdown voltage of Insulating pressphan paper is also higher compared to all other insulating papers used in oil-cooled transformers.

Transformer Insulating Diamond dotted epoxy paper

Transformer Insulating Diamond dotted epoxy paper is a variety of transformer insulating kraft paper or pressphan paper on which epoxy resin square dots are impregnated at a certain distance. When this paper is used to make coils and such coils are subjected to heat in ovens to remove excess moisture from transformer parts, the epoxy resin melts above 100 deg C and binds the conductors around it. This is very useful in preventing the dislocation of conductors due to vibrations when the transformer is in operation in the field.

Transformer Insulating crepe paper

Transformer Insulating crepe paper is insulating kraft paper which is creped using a special machine and chemical. This process makes the paper stretchable by up to 80 to 120% of its original length when pulled laterally. Transformer Insulating crepe paper is used in covering lead-outs in power transformers, in covering the core of instrumentation transformers and also in covering of rectangular profile conductors for single-phase transformers.