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Construction Low Voltage Winding of a distribution transformer Low voltage windings are usually made of copper STRIP OR FOIL. The benefit of this is that any high voltage ampere-turn asymmetry which might occur is compensated automatically by an appropriate internal current distribution in the low voltage foil.This reduces the axial stresses produced by short-circuits to a minimum (down to 10% of those for conventional windings), thus enabling the axial support construction to be greatly simplified. The sheets and connectors welded onto them are made of electrolytically pure copper with a rigorously guaranteed conductivity. Designs are adapted to the thermal, electrical and chemical characteristics of each type of conductor, thus ensuring that both versions are of equivalent quality, whether made of copper. The maximum voltage between each turn is only a few tens of volts. This allows the insulation needed between the turns (foils) to be limited to 2 OR 32 sheets of fine kraft paper only a few hundredths of a millimeters thick. According to the design specification, this insulation may be coated with a thermo- hardening epoxy adhesive which cures and bonds during the drying process. Types of winding use can be Duplex Winding, Cross Over Winding, Helical Winding, Disc Winding, Pre-Transpose Winding, Multi Layer Winding.


Type of Winding

Duplex  Cross over; Helical Disc;
Parallel Layer  Pre- Transpose;
Multi-Layer  Interleaved Disc Winding


Type of Insulation

average winding temperature rise

A 55°C
B 80“ C

The main benefits of layered windings are: They form a simple winding, which allows continuous or semi-automatic winding. The impulse voltage distribution throughout the winding is predictable and controlled. Axial cooling ducts are simple to build and fit. Any taps required can be brought out anywhere in the winding through the layers.

High Voltage Windings

High voltages windings are almost exclusively of layered construction. The copper conductors are made of one or more round or square wires, either with an insulating enamel coating or wrapped in insulating paper. Each design is drawn up in accordance with the specific characteristics of conductor material to be used. The insulation between the layers consists of pre-coated kraft paper, applied either in sheet form or wound in a continuous narrow strip, a technique which allows optimum adjustment of the insulation thickness to the electrical gradient at each layer position. The special diamond pattern or epoxy adhesive coated onto the kraft paper cures during the drying process, bonding the windings into a single structure. This mechanical strength is of the utmost importance since, in the event of short-circuit, the windings have to sustain very high radial repellent forces. The mechanical effect of these forces is minimal in round windings, since these windings inherently have the ideal form to withstand radial stresses. The mechanical effect is much greater in rectangular windings.