Manufacturing PProcess Coil Core Form Coil is designed and manufactured to withstand the impulse voltage and prevent it from distortion when a short circuit occurs. Conductors will be transposed at sufficient intervals to minimize currents and equalize the current and temperature distribution along the winding. Shell Form The narrow high-dielectric strength paper is spirally wound in several overlapped layers by winding machine around each strand and layer of subdivided conductors. The outermost paper tape layer has a thermosetting coating. This bonds the coils after clamping and ovendrying to insure mechanical strength and freedom from shifting of turns during assembly. Insulation Core Form The reliability of transformers depends principally on the quality of the insulation system. The insulation system has to meet the following requirements:high dielectric strength, low partial discharge levels, mechanical stability, efficient heat dissipation and long-lasting durability. Shell Form Pressboard sheets, having high dielectric strength when oil impregnated, are formed into channels, washers and spacer block assemblies. These are interleaved around and between the coils during stacking to insure adequate electrical clearances and oil flow. The pressboard insulation is only used in compression. Core Construction Core Form The most important part of construction of core is having high permeability and low hysteresis. Structural rigidity is given to the structure material of core form’s core by the use of steel plates at the bottom of the core. Therefore, distortion due to short circuit stresses or transport handling can be prevented. Shell Form The core material is Hipersil, a cold rolled, grain-oriented, highly permeable, annealed and non-aging silicon steel that will carry one third more flux per unit area than ordinary electrical steel. Each lamination is coated with inorganic insulator.