In this edition of Ask the Legends, the engineering team at New England Wire Technologies breaks down the fundamentals of the skin effect in alternating current (AC) circuits and explains why it is a critical consideration when designing high-frequency magnetic components.
In direct current (DC) circuits, electrical current flows uniformly through the entire cross-sectional area of a conductor. However, when alternating current flows through a wire, the alternating magnetic field generates internal eddy currents that oppose current flow in the center of the conductor. As operating frequencies rise, electrons are progressively pushed away from the core and forced to travel within a thin outer layer or “skin” along the wire’s perimeter.
This current crowding causes two primary issues in electromagnetic systems:
- Reduced Effective Conductor Area: Because the center of the conductor carries little to no current, the active conductive cross-section shrinks dramatically.
- Surging AC Resistance ($R_{AC}$): With less copper actively carrying current, effective resistance increases significantly. According to Joule’s Law ($P = I^2R$), this increased resistance converts electrical energy into wasted heat, degrading overall system efficiency.
Litz wire solves the skin effect by replacing a single heavy conductor with dozens, hundreds, or thousands of microscopic, individually enamel-insulated strands. By sizing each strand’s radius to be smaller than the calculated electromagnetic skin depth ($\delta$) at the specific operating frequency, the skin effect cannot develop within the individual wires. Furthermore, carefully engineered weaving or twisting ensures that all strands share current equally throughout the entire cross-section of the bundle, maintaining low AC resistance and high efficiency in high-frequency transformers, inductors, and motors.
Key Technical Takeaways
- Skin Effect Mechanism: Internal eddy currents generated by alternating magnetic fields push current outward, concentrating electron flow along the conductor’s surface.
- Frequency-Dependent Depth: As operating frequency increases, the conductive skin depth ($\delta$) decreases, rendering the center of solid conductors non-functional.
- Thermal & Efficiency Losses: Shrinking the effective conductive area causes a sharp spike in AC resistance ($R_{AC}$) and dissipates substantial power as waste heat.
- Litz Wire Countermeasure: Using fine strands sized smaller than the operating skin depth allows each strand to carry current uniformly across its entire cross-section.
- Uniform Current Sharing: Geometric twisting and transposing of individually insulated strands ensures balanced inductance and equal current distribution throughout the bundle.
Episode Transcript – What is Skin Effect? Ask the Legends
Welcome to Ask the Legends
Welcome to “Ask the Legends: The Legends of Litz.”
Today we’re here to talk about the skin effect and why it’s important in choosing a Litz cable.
Understanding the Skin Effect
When alternating current, or AC, flows through a conductor, something interesting happens, especially at high frequencies.
Instead of the current spreading evenly across the wire’s cross-section, it tends to concentrate near the surface of the conductor. This is called the skin effect. The higher the frequency, the more pronounced it becomes.
Why Skin Effect Matters: AC Resistance & Heat Losses
Why does it matter? Well, when the current is forced to flow only on the surface, the effective area of the conductor shrinks and the resistance increases. That means more energy is wasted as heat, which isn’t exactly ideal for efficiency.
How Litz Wire Eliminates the Skin Effect
This is where Litz wire comes to the rescue.
Litz cables are made of many thin, individually insulated strands, twisted or braided together. Each strand is small enough that the skin effect doesn’t limit current flow to just the surface. Plus, the unique weaving ensures all the strands share the current more evenly.
Performance Benefits for High-Frequency Systems
The result? Lower AC resistance, reduced power loss, and better performance in high-frequency applications like transformers, inductors, and motors.
So whenever efficiency at high frequencies is a priority, Litz cables are the go-to solution for minimizing the impact of skin effect.
Thank you for joining me. If you have any more questions, please feel free to contact us.
