34 affected area is required to be small, the welding area is 80% of the crosssectional area and the pull-out force is generally about 600–800 N. S-winding / D-pin S-winding uses a continuous conductor that is preformed into a wave shape before being compressed into the stator slots. Unlike standard hairpins that require hundreds of laser welds on the crown of the motor, the S-winding is continuous. This removes hundreds of potential failure points. The head of the motor (the part sticking out of the slots) is also much shorter, allowing for a more compact motor housing. The implementation involves a winding mat that is preformed into a continuous wave and then inserted into the stator in a single motion or wound in radially. The primary technical benefit is the elimination of hundreds of weld points. Because the wire is continuous, the reliability of the stator is inherently higher, and the end turns – the copper sticking out of the slots – are significantly shorter, making the motor more compact. However, the machinery required to form a flat-wire wave without damaging the delicate enamel insulation is incredibly complex and less flexible for different motor sizes compared with that of standard hairpin lines. However, managing a long, continuous wave of copper and forcing it into slots without damaging the insulation is a manufacturing challenge. The S-winding also cannot reach the absolute maximum density of individual I-pins because the copper needs a wider tolerance to be woven. What sets continuous hairpin winding apart from traditional winding methods is its ability to reduce manufacturing complexity. The conventional hairpin design typically requires multiple assembly steps, including numerous welded joints, which can be prone to failure. By eliminating most of these welding points, continuous hairpin technology not only improves reliability but also enhances design freedom. The drive for higher power densities, particularly in high-speed electric machines, is reshaping the manufacturing sector. Continuous hairpin winding is a key enabler in this evolution. It simplifies the complex winding process of traditional hairpins, offering a more streamlined and efficient approach, which is essential for high-speed, high-voltage applications. For OEMs, this holds significant promise. A more efficient motor requires fewer raw materials and has reduced weight, enabling OEMs to offer cost-effective products without compromising on performance.” Continuous hairpin winding CHW features a single rectangular conductor that is twisted continuously to create one entire phase branch. This eliminates most welding points per branch compared with conventional hairpin windings, lowers the risk of insulation degradation, improves cooling quality and reduces winding loss. This has been combined with a flat lamination bending technique, eliminating the need to fit windings into the cylindrical stator. To further improve the compactness of end winding, a stepwise CHW has the terraced end turns shortened to reduce the DC winding resistance. The same geometry also eliminates inter-coil interference and promotes better coolant circulation. Guiding fixtures steer each sinusoidal conductor through the lamination stack while pre-interweaving multiple wires prior to insertion can provide more compact and mechanically robust assembly. CHW features the same AC loss mechanisms found with its counterparts. At the conductor level, the AC loss is induced by the skin and proximity effect under the influence of the in-slot magnetic field. At bundle level, additional AC loss could be generated when different parallel branches feature asymmetric impedance. This is embodied as circulating current between branches, and can be effectively mitigated by using specific layout design rules. CHW can be designed with higher slot numbers and winding layer numbers, but is more easily subject to additional circulating current-induced AC loss due to its more problematic design. Another factor is that radial-insertion windings such as CHW require an openslot stator. This increases slot-leakage reactance and typically elevates AC loss of conductors near the slot opening area. Magnetic or hybrid wedges can reduce the slot leakage flux, but they introduce extra cost and assembly steps. These open-slot penalties diminish as the slot number rises, making CHW particularly well suited to the high slot number, high frequency machines July/August 2026 | E-Mobility Engineering Hairpins in an electric motor (Image: Honest Automation)
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