four types of motor flat wire windings

Four Types of Motor Flat Wire Windings

When it comes to optimizing the efficiency and performance of electric motors, the design of the stator winding plays a crucial role. Flat copper wire windings, compared to traditional round wire windings, offer improved filling factors within motor slots, thereby enhancing motor efficiency.  This article delves into the specifics of four types of flat wire windings, namely I-pin, Hair-pin, X-pin, and S-winding. Each type possesses unique characteristics impacting motor efficiency, power density, and manufacturing complexity.

I-pin Winding

The I-pin winding, resembling the letter ‘I’, involves the direct insertion of wires followed by dual-side welding. Also known as the double-layer cavity winding, it employs a complex structural design to maximize slot utilization. 

By alternating two different-direction windings within stator slots, the I-pin winding ensures tight wire packing and reduces electromagnetic noise and vibrations.

Advantages of I-pin winding include enhanced slot fill rate, minimized hot spots, improved thermal dissipation, and uniform winding distribution.

However, its manufacturing cost is relatively high due to intricate welding processes and the requirement for precise winding techniques and equipment.

I-pin winding

Hair-pin Winding

Hair-pin winding, resembling a hairpin, involves pre-forming wires into an ‘H’ shape before insertion and single-side welding. This widely-used flat wire winding offers higher filling factor and power density compared to I-pin winding.

Its compact structure, facilitated by wire connections through copper strips, reduces resistance, inductance, and capacitance effects, thereby enhancing motor efficiency.

Despite its benefits in high-power and high-efficiency applications, Hair-pin winding entails complex manufacturing processes and demands specialized winding equipment and techniques. Its widespread adoption necessitates a careful balance between advantages and manufacturing costs.

hair-pin winding

X-pin Winding

Similar to Hair-pin winding, X-pin winding involves bending wires into an X shape, then fixing them through connectors or welding. Each X-pin unit is independent, allowing for shorter ends and higher filling factor within the same space.

Despite maintaining similar insertion dimensions as Hair-pin winding, X-pin winding reduces end sizes by 5-10mm after welding, improves power density, and further enhances motor efficiency by lowering copper losses.  The manufacturing process is simpler than wave winding.

However, the short welding ends of X-pin winding pose challenges in welding processes, as well as issues like wire breakage and twisting during manufacturing.

X-pin winding


S-winding involves arranging adjacent coils in an ‘S’ shape and installing them sequentially on the stator without welding at both ends.

With fewer weld points and smaller end space requirements, S-winding offers advantages in terms of reduced electromagnetic noise(NVH), uniform magnetic field distribution, reduced torque ripple, and improved stability and ventilation for better stator heat dissipation.

However, S-winding demands more copper wire and intricate manufacturing processes, along with higher requirements for winding equipment and techniques.



In conclusion, the choice of winding design significantly impacts the performance and efficiency of electric motors.

Each type of flat wire winding, whether it’s the complex yet efficient I-pin, the widely-adopted Hair-pin, the space-efficient X-pin, or the noise-reducing S-winding, offers unique advantages and challenges.

Understanding these variations helps engineers optimize motor designs for specific applications, balancing performance, efficiency, and manufacturing costs effectively.


What are the application areas of flat wire motor and round wire motor?

Flat wire motors find applications in various industries requiring high efficiency and power density, such as automotive, aerospace, and industrial automation. Their motor winding compact design and improved slot filling make them ideal for electric vehicles(new energy vehicles), robotics, and high-speed machinery. 

Round wire motors, on the other hand, are more commonly used in conventional household appliances, fans, pumps, and simple industrial applications where cost-effectiveness and simplicity are prioritized over high performance and efficiency.

What are the advantages of flat wire windings over traditional round wire windings?

Flat wire windings offer better filling factor within motor slots, leading to improved efficiency, high power density, and reduced electromagnetic noise.

Are there any disadvantages to using flat wire windings?

While flat wire windings offer advantages in efficiency and power density, they may require more complex manufacturing processes and incur higher costs compared to round wire windings.

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