How does insulation foil suppress eddy current losses and maintain dielectric stability in high-frequency transformers?
Publish Time: 2026-02-18
With the rapid development of power electronics technology towards higher frequencies, smaller sizes, and higher efficiency, high-frequency transformers, as core magnetic components in switching power supplies, new energy inverters, and electric vehicle drive systems, directly determine the overall energy efficiency and reliability of the system. Insulation foil, as a key insulating material between windings, layers, and ground in high-frequency transformers, not only needs to provide reliable electrical isolation but also needs to effectively suppress eddy current losses and maintain long-term dielectric stability in high-frequency alternating electromagnetic fields.
1. Low-conductivity substrate fundamentally suppresses eddy current generation.
Eddy current losses originate from the circular current induced in conductors or high-dielectric-constant materials by alternating magnetic fields. Traditional insulating materials containing trace amounts of metallic impurities or having a high dielectric loss tangent can become "quasi-conductors" at high frequencies, exacerbating energy loss and localized heating. High-performance insulation foil typically uses high-purity organic films such as polyimide, polyester, or aramid paper as the substrate. This intrinsic low conductivity and low polarization significantly weaken the conditions for eddy current path formation at the source, effectively reducing additional losses.
2. Ultra-thin and Multilayer Composite Structures Optimize Electromagnetic Distribution
In high-frequency transformers, the skin effect and proximity effect of the windings are significant, causing current to concentrate on the conductor surface and resulting in a highly uneven magnetic field distribution. By precisely controlling the thickness of the insulation foil, the interlayer spacing of the windings can be reduced, thereby reducing leakage inductance. Simultaneously, its uniform and dense structure avoids localized electric field concentration caused by air gaps. Furthermore, high-end applications often employ an "insulation foil + nano-alumina coating" or "PI/PET double-layer composite" structure: the former improves the surface corona resistance, while the latter utilizes the difference in dielectric parameters of different materials to smooth the electric field gradient and suppress partial discharge. This microstructure design achieves active control of the electromagnetic field distribution without sacrificing flexibility.
3. Dielectric Stability Depends on Material Thermo-Electrical Coupling Performance
Under high-frequency operation, insulation foil is subjected to the dual stresses of alternating electric fields and temperature rise, making it prone to aging, carbonization, and even breakdown. Insulation foil must possess excellent thermal stability and corona resistance. Its molecular chain structure is highly stable, making it less prone to breakage and free radical generation at high temperatures. Simultaneously, surface treatment with plasma or chemicals enhances the interfacial bonding with copper foil or magnetic core, preventing microcracks caused by thermal expansion coefficient mismatch—these micro-defects are often the starting point of dielectric failure. Furthermore, some insulation foils are doped with inorganic nanoparticles, which not only improve thermal conductivity to accelerate heat dissipation but also trap high-energy electrons through a "trap effect," delaying the electrical dendrite process.
4. System-Level Synergy: Matching Insulation Foil with Winding Technology
The performance of insulation foil depends on deep synergy with transformer manufacturing processes. For example, during automated winding, insulation foil needs to possess good mechanical strength and tear resistance to prevent damage caused by tension fluctuations. During vacuum impregnation or potting, its surface energy must be compatible with the resin system to ensure no air bubbles remain. More importantly, it's crucial to rationally select insulation classes that match the operating frequency range to avoid over-design or under-protection. By using simulation software to jointly analyze the electric and temperature fields, the number, position, and overlap of insulation foil layers can be optimized, achieving maximum safety margin with minimal thickness.
In summary, insulation foil in high-frequency transformers, through its intrinsic properties of low-loss materials, precise microstructure design, synergistic stability across thermo-electric-mechanical fields, and high compatibility with manufacturing processes, has successfully achieved effective suppression of eddy current losses and long-term reliability of dielectric properties. As wide-bandgap semiconductor devices drive switching frequencies towards the MHz level, the performance requirements for insulation foil will continue to escalate, and its technological innovation will become a key support for overcoming energy efficiency bottlenecks in high-frequency magnetic components.
