Challenges and Future opportunities of Hairpin Technologies

Abstract

Hairpin windings are seeing an ever-increasing application and development in electrical machines designed for high power and torque densities. In fact, due to their inherently high fill factor, they are very attractive in applications, such as transportation, where these characteristics are considered main design objectives. On the other hand, high operating frequencies also contribute to improve power density of electrical machines. However, at high fundamental frequencies, hairpin windings are characterised by increased Joule losses due to skin and proximity effects. Hence, while these technologies are introducing new opportunities, a number of challenges still need to be addressed. These include manufacturing aspects, contacting processes, thermal management, etc. This paper presents an overview of the current state-of-the-art of hairpin technologies and propose possible future opportunities. The authors' perspective is then finally provided, showing how innovative winding patterns can potentially overcome the above mentioned challenges.

Partial Discharges in Electrical Machines for the More Electrical Aircraft. Part III: Preventing Partial Discharges

“…Conventional hairpin windings do not perform well at high frequency, as proximity and skin effects contribute to increase the equivalent winding resistance (AC resistance) and thus power losses, preventing their use in such applications. However, innovative hairpin solutions, which minimize power losses at high frequency, have been proposed in [34] and [35], with promising results also for the aerospace sector.…”

Hairpin Windings: Sensitivity Analysis and Guidelines to Reduce AC Losses

“…The combination of (3) and ( 4) results in the final expression in (5), whose general solution is provided in (6). Here, p is as defined in (7), where δ is the skin depth reported in (8).…”

“…This level of flexibility cannot be achieved when using bar-wound windings (namely the hairpin winding) [8]. Due to their pre-formed nature, the subdivision in strands cannot be flexibly applied, the number of turns is always even and the maximum number of conductors per slot is limited.…”

Slot Design Optimization for Copper Losses Reduction in Electric Machines for High Speed Applications

“…The current density distribution and the Joule losses can be analytically evaluated as a function of the operating frequency for a single rectangular slot without the polar shoes. Alternative hairpin winding layouts are taken into account in the model developed in [7].…”

“…The design of the parallel paths requires a proper methodology to mitigate the additional losses and the current density distribution issues. The authors of [6] propose a method denoted as transposition, while other design methods have already been discussed and proposed to overcome these challenges [7].…”