Capacitance¶

Parasitic (stray) capacitance in magnetic components affects: - High-frequency behavior and resonances - EMI performance (common-mode noise paths) - Switching transients in power converters - Self-resonant frequency of inductors

MKF models several capacitance components: - Turn-to-turn capacitance: Between adjacent turns - Layer-to-layer capacitance: Between winding layers - Winding-to-core capacitance: Between windings and grounded core - Primary-to-secondary capacitance: Coupling between windings

Available Models¶

Koch¶

Koch's model uses parallel-plate approximation with fringing corrections:

\[C = \varepsilon_0 \varepsilon_r \frac{A}{d} \cdot k_{fringe}\]

Where \(k_{fringe}\) accounts for field spreading at conductor edges. Good for turn-to-turn and layer-to-layer capacitance.

Reference: Koch et al. 'Stray Capacitance in Inductors.' IEEE Trans. Power Electronics, 2020

Massarini¶

Massarini's analytical model for winding capacitance includes: - Multi-layer effects - Wire geometry (round, rectangular) - Insulation thickness

Provides separate formulas for different capacitance components.

Reference: Massarini, Kazimierczuk. 'Self-capacitance of inductors.' IEEE Trans. Power Electronics, 1997

Albach¶

Albach's comprehensive capacitance model accounts for: - 2D field distribution - Non-uniform winding spacing - Core proximity effects

Provides good accuracy across various winding configurations.

Reference: Albach et al. 'Calculating stray capacitance.' IEEE Trans. Magnetics, 2011

Duerdoth¶

Duerdoth's coil self-capacitance model uses energy-based approach:

\[C_{self} = \frac{2 W_E}{V^2}\]

Where \(W_E\) is the electric field energy stored between turns.

Reference: Duerdoth, W.T. 'Equivalent Capacitance of Transformer Windings.' Wireless Engineer, 1946

Model Comparison¶

Model	Error	Reference

Capacitance Minimization Strategies¶

Technique	Effect	Trade-off
Increase turn spacing	Reduces turn-to-turn C	Larger winding window
Section winding	Reduces layer-to-layer C	More complex construction
Shield windings	Controls coupling paths	Additional losses
Bank winding	Reduces distributed C	Higher leakage inductance
Thicker insulation	Reduces all C	Thermal resistance

Default Model: Albach provides good balance of accuracy and generality.