The high-voltage transformer windings are wound from 1060 1070 aluminum foil strip interleaved with high-grade insulating foils. The assembled and connected individual coils are placed in a heated mold and are potted in a vacuum furnace with a mixture of pure silica (quartz sand) and specially blended epoxy resins. The only connections to the outside are casted brass nuts that are internally bonded to the aluminum winding connections.
The external delta connections are made of insulated copper or aluminum bus bar connectors to guarantee an optimal installation design. The resulting high-voltage windings are fire-resistant, moisture-proof and corrosion-proof, and they show excellent aging properties under all operating conditions.
The aluminum foil strip for HV transformer windings combine a simple winding technique with a high degree of electrical safety. The insulation is subjected to less electrical stress than in other types of windings. In a conventional round-wire winding, the interturn voltages can add up to twice the interlayer voltage. In a foil winding, it never exceeds the voltage per turn, because a layer consists of only one winding turn. This results in high AC voltage and impulse voltage withstand capacity.
Aluminum foil strip for HV transformer winding is used because the thermal expansion coefficients of aluminum and cast resin are so similar that thermal stresses resulting from load changes are kept to a minimum.
