In this edition of Ask the Legends, the engineering team at New England Wire Technologies explains the mechanics of the proximity effect and how it degrades electrical efficiency in high-frequency windings.
The proximity effect occurs when two or more conductors carrying alternating current (AC) are placed in close physical proximity. Every AC-carrying conductor generates an alternating magnetic field around itself. When these conductors are tightly bundled—such as in a transformer bobbin, motor stator, or multi-layer inductor coil—their varying magnetic fields interact and penetrate neighboring conductors.
This external magnetic field induces localized eddy currents that distort the flow of electrons, forcing current to crowd into concentrated regions of the conductor’s cross-section rather than distributing uniformly. Key consequences include:
- Constricted Conduction Area: Current crowding drastically reduces the effective cross-sectional area of the copper.
- Elevated AC Resistance ($R_{AC}$): Higher resistance generates excess Joule heating ($I^2R$ losses).
- Compounding High-Frequency Losses: While the skin effect is caused by a conductor’s own internal magnetic field, the proximity effect is driven by adjacent fields. In multi-layer coils, proximity effect losses often far exceed skin effect losses as operating frequencies climb into the tens and hundreds of kilohertz.
Litz wire neutralizes the proximity effect through two core design features:
- Individual Strand Dielectric Enamel: Microscopic enamel coatings on every strand block transverse current flow between adjacent wires, preventing localized eddy currents from circulating across the bundle.
- Geometric Transposition: Carefully engineered braiding and twisting patterns ensure that every strand shifts uniformly between internal and external positions along the length of the bundle. This equalizes exposure to neighboring magnetic fields, balances strand inductance, and ensures uniform current distribution across the entire conductor.
Key Technical Takeaways
- Interacting Magnetic Fields: Caused by adjacent AC-carrying conductors whose alternating magnetic fields penetrate one another.
- Current Crowding Mechanism: Induces circulating eddy currents that push electron flow into localized sections of the conductor, leaving other areas inactive.
- Accelerated AC Resistance: Drastically increases alternating current resistance ($R_{AC}$) and thermal energy dissipation in tightly wound coils.
- Proximity vs. Skin Effect: Skin effect is self-induced within a single isolated wire; proximity effect is caused by the external magnetic fields of adjacent turns and layers.
- Litz Wire Countermeasure: Individually insulated strands prevent transverse current loops, while geometric transposition equalizes field exposure to maintain uniform current sharing.
Episode Transcript – What is Proximity Effect? Ask the Legends
Welcome to Ask the Legends
Welcome to “Ask the Legends: The Legends of Litz.”
Today’s question is: what is proximity effect?
The Mechanics of Interacting Magnetic Fields
Let’s talk about the proximity effect and how it comes into play with conductors, especially at high frequencies.
So, we’ve all heard of magnetic fields around wires when current flows through them, right? Well, when two or more conductors are placed close to each other, their magnetic fields start to interact.
This interaction can distort how the current flows through the wires, concentrating in certain areas instead of spreading evenly. This is called the proximity effect.
High-Frequency Resistance and Coil Inefficiency
Like the skin effect, it becomes more significant as frequency increases.
The result is increased resistance and more energy losses, which isn’t something you want in a transformer or an inductor.
How Litz Wire Neutralizes Proximity and Skin Effects
Here’s where Litz wire saves the day again.
Since Litz cables are made of thin, insulated strands woven together, they break up these localized currents caused by the proximity effect. The insulation prevents the strands from directly interacting with each other’s magnetic fields, and the weaving ensures the current is distributed more evenly.
Bottom line, Litz cables minimize both proximity effect and the skin effect, making them a top choice for high-frequency applications where efficiency is key.
If you have any more questions, please feel free to contact us.
