Disc Windings

Turns wound perpendicular to the core axis, forming individual discs connected in series. Dedicated oil ducts between discs ensure effective cooling. Interleaved configurations available for improved impulse voltage distribution.

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Design Rationale

Disc windings are characterised by turns wound perpendicular to the core axis, forming individual discs connected in series and arranged along the axial direction. Dedicated oil ducts are created through spacers between adjacent discs, providing highly effective and geometrically predictable cooling across the full winding height.

This construction is primarily used in high-voltage applications where the combination of high dielectric stress, impulse voltage performance and mechanical withstand under short-circuit forces demands a winding geometry superior to layer construction. Disc windings can be manufactured using either rectangular conductors or continuously transposed cables (CTC), with the conductor choice driven by the current level and additional loss requirements of each specific design.

Through interleaved disc configurations, the series capacitance of the winding can be significantly increased. This modifies the initial voltage distribution under lightning impulse conditions, bringing it closer to the uniform distribution – reducing voltage stress concentration in the end discs and improving the impulse withstand margin across the entire winding.

Key Engineering Features

Series Disc Architecture

Individual discs connected in series along the axial direction distribute the total winding voltage uniformly across the disc stack, providing controlled inter-disc voltage stress at every operating condition.

Interleaved Configuration

Interleaving adjacent disc turns increases the series capacitance of the winding, improving initial voltage distribution under lightning impulse (BIL) – a critical parameter for transformers at high voltage classes.

Axial Oil Duct Cooling

Spacers between adjacent discs create geometrically defined axial oil ducts, ensuring uniform oil flow distribution and predictable temperature gradient across the full winding height.

Short-Circuit Withstand

Disc geometry distributes axial and radial electromagnetic forces over a large number of conductor interfaces, providing superior short-circuit mechanical strength compared to layer construction at equivalent voltage and power.

Technical Note

Interleaving and Impulse Performance – The initial voltage distribution in a disc winding under impulse is governed by the ratio of series-to-ground capacitance (α factor). Standard disc windings have an inherently non-uniform initial distribution, concentrating stress on the line-end discs. Interleaving rearranges the turn sequence within each disc to increase series capacitance without modifying the winding’s electrical parameters, bringing the distribution coefficient Kd closer to 1.0. The degree of interleaving required is determined during the electromagnetic design phase based on the BIL class and the winding’s capacitance geometry.

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