In Dry Cast resin transformers, spiral wound tubes made of DMD, Nomex® and Mylar® are used to insulate the tie rods.
In all types of transformer manufacturing it is important to insulate electrically the tie rods that keep the packs of laminated steel compressed, so that induced electric currents are not generated in the tie rods themselves.
These currents can be induced by electric flows produced by some windings that do not complete the flow chaining with the other windings.
This means that some electromagnetic fluxes can then be closed through the air; they can reach the tie rods, crossing them and generating a difference of potential that can cause dangers to the transformers.
Politubes insulating tubes are used to avoid this problem on transformers tie rods and guarantee the correct operation.
These insulation tubes are supplied with a wall thickness between 0,5 and 1 mm in order to ensure a higher insulation and guarantee mechanical rigidity.
In oil type transformers, it is preferred crepe Nomex ® tube because it is softer, more easily “shrinkable” and oil-impregnated; in this application our insulation tube is used to cover the primary/secondary connection cables.