Concentric vs. Interleaved Windings: Which Transformer Design is Right for Your Application?
Concentric vs. Interleaved Windings: Which Transformer Design is Right for Your Application?
In the field of transformer design, the choice of winding arrangement has a decisive impact on equipment performance, efficiency, and application range. Concentric windings and interleaved windings are two of the most common winding configurations, widely used in power transformers, distribution transformers, and special reactors. Understanding their differences not only helps engineers optimize designs but also assists users in making more informed decisions during product selection.
1. Basic Structural Differences and Definitions
1.1 Concentric Windings: The Traditional Layered Layout
Concentric windings refer to a structure where coil windings are arranged in layers around a common central axis, typically organized by voltage level or function. This layout originates from early transformer design, featuring an intuitive structure and relatively mature manufacturing processes.
Structural Principle and Physical Layout Concentric windings adopt a radial layered arrangement. For example, in a typical power transformer:
(1) Inner Layer (Low-Voltage Side):
Usually wound directly onto the transformer core. Due to the lower voltage, it requires less insulation distance and can be placed close to the core.
(2) Outer Layer (High-Voltage Side):
Wrapped around the inner layer winding. The higher voltage necessitates more insulation space and materials.
This “inside-out” arrangement utilizes the basic principle of electromagnetic induction: when alternating current flows through any winding, it generates an alternating magnetic flux in the core, which then couples to the other winding to achieve voltage transformation. The concentric structure results in a relatively concentrated magnetic path, but the electromagnetic coupling distance between the windings is greater.
1.2 Interleaved Windings: The Modern Alternating Design
Interleaved windings represent an advanced layout where the high-voltage and low-voltage windings are divided into multiple sections and alternately arranged along the axial direction of the core. For instance, a winding might be split into 4 segments, with high-voltage and low-voltage sections placed alternately. This design breaks away from the traditional concept of radial layering, moving towards axial segment interleaving.
1.2.1 Structural Principle and Arrangement Logic
The core idea behind interleaved windings is to reduce the leakage magnetic distance between windings, thereby improving electromagnetic coupling efficiency. By placing high and low-voltage winding sections alternately, each low-voltage section is positioned adjacent to a high-voltage section. This allows the magnetic field to pass more directly between them, reducing leakage flux.
1.2.2 Coupling Coefficient Formula
Calculation Formula and Coupling Coefficient Improvement The coupling coefficient (k) is a key parameter for measuring the energy transfer efficiency between windings, calculated as
k = M / √(L1 × L2)
where M is the mutual inductance
L1, L2 are the self-inductances of the high-voltage and low-voltage windings, respectively.
In the interleaved design, because the distance between winding sections is reduced, the mutual inductance M increases significantly, leading to a higher coupling coefficient k. This means more magnetic energy is used for effective transfer rather than being lost as leakage flux.
2. Performance Comparison and Working Principle Differences
To clearly show the key performance differences between the two winding types, the following table provides a comparison across multiple dimensions:
| Feature Dimension | Concentric Windings | Interleaved Windings |
| Electromagnetic Coupling Efficiency | Lower, higher leakage flux | Higher, significantly reduced leakage flux |
| Short-Circuit Impedance | Relatively higher | Can be designed to be lower |
| Heat Dissipation Performance | Possible larger temperature difference between layers | More uniform heat distribution |
| Manufacturing Complexity | Relatively simple, mature process | More complex, requires precise segmentation |
| Suitable Voltage Levels | Common in medium/high-voltage, high-capacity transformers | Especially suitable for low-impedance, high-frequency applications |
| Cost Factors | Lower material cost, standard insulation requirements | Potentially higher manufacturing cost |
2.1 Electromagnetic Performance and Efficiency Impact
2.1.1 Leakage Flux and Short-Circuit Impedance
In concentric windings, the radial distance between high and low-voltage windings is larger, resulting in greater leakage flux. Leakage flux not only reduces coupling efficiency but also increases the short-circuit impedance. While higher short-circuit impedance helps limit short-circuit current, it can also lead to higher voltage regulation and losses.
Interleaved windings minimize the average distance between high and low-voltage windings through alternating arrangement. According to Ampère’s circuital law and the principle of magnetic field superposition, the magnetic fields generated by adjacent segments enhance effective coupling, and the leakage magnetic path is significantly shortened. Therefore, designers can more flexibly control the short-circuit impedance, making this design more suitable for applications requiring low impedance and high dynamic response, such as certain Variable Frequency Drive (VFD) power supplies or special reactors.
2.1.2 Eddy Current Loss and High-Frequency Characteristics
Eddy current loss is related to the frequency and strength of the changing magnetic field. In concentric windings, uneven distribution of the leakage magnetic field can cause higher eddy current losses in local areas. Due to its more uniform magnetic field distribution, interleaved windings can reduce local overheating and eddy current losses, performing particularly well under high-frequency or harmonic-rich operating conditions (e.g., renewable energy inverter transformers).
2.2 Thermal Management and Heat Dissipation Characteristics
2.2.1 Heat Distribution and Cooling Effectiveness
Heat in concentric windings often distributes in layers: the inner winding, close to the core, has a longer heat dissipation path; the outer winding is in direct contact with the cooling medium (like transformer oil or air), allowing better heat dissipation. This temperature difference can lead to local hot spots, affecting insulation lifespan.
In interleaved windings, the alternating arrangement of high and low-voltage sections results in a more uniform distribution of heat sources. Each section has a more direct cooling channel, reducing the overall temperature gradient. This layout aligns well with international requirements for transformer temperature rise limits, such as IEC 60076-7, helping to improve long-term equipment reliability.
2.2.2 Insulation System and Thermal Aging
The thermal aging rate of insulation materials follows the Arrhenius equation: the aging rate increases exponentially with temperature. If local overheating occurs in concentric windings, it may accelerate insulation aging in that area. The uniform heat distribution in interleaved windings results in more consistent overall insulation temperatures, delaying the overall aging process and meeting global expectations for transformer lifespan (typically designed for 25-30 years).
Conclusion
Concentric windings and interleaved windings represent two paths in transformer design: classic and innovative. Concentric windings are known for their simplicity and reliability, suitable for most traditional power applications. Interleaved windings, with their advantages of high efficiency and compactness, are increasingly becoming the preferred choice for high-frequency, high-efficiency applications. Choosing the right transformer winding type—whether concentric winding for robust, cost-effective solutions or interleaved winding for superior performance in demanding conditions—is crucial for optimal power transformer design and application success.
Contact
LuShan, est. 1975, is a Chinese professional manufacturer specializing in power transformers and reactors for 50+ years. Leading products are single-phase transformer, three-phase isolation transformers, electrical transformer, distribution transformer, step down and step up transformer, low voltage transformer, high voltage transformer, control transformer, toroidal transformer, R-core transformer; DC inductors, AC reactors, filtering reactor, line and load reactor, chokes, filtering reactor, and intermediate, high-frequency products.
Our power transformers and reactors are widely used in 10 application areas: rapid transit, construction machinery, renewable energy, intelligent manufacturing, medical equipment, coal mine explosion prevention, excitation system, vacuum sintering(furnace), central air conditioning.
Know more about power transformer and reactor: www.lstransformer.com.
If you would like to obtain customized solutions for transformers or reactors, please contact us.
WhatsApp：+86 13787095096
Email: marketing@hnlsdz.com
