Experimental Determination of Conductor Lay and Impact on AC Loss in Volume Manufactured Machines using X-Ray Computed Tomography

Abstract

The volume manufacture of power-dense electrical machines results in a random conductor lay throughout the stator winding and stator slots, which is unknown and varies from slot-to-slot. The AC losses of such windings are sensitive to the specific conductor lay present within the stator slot. However, limited data is currently available regarding the actual conductor lay observed in 'asmanufactured' windings. This paper presents the novel application of X-ray Computed Tomography to characterize the conductor lay in a wound prototype plastic stator. Preliminary results indicate that limited strand transposition occurs in the stator active length, compared to the significant strand transposition present in the end winding region. Variability in strand compaction in the stator slot is also identified as a contributary factor to the variability observed in AC losses.

Designing for Conductor Lay and AC Loss Variability in Multistrand Stator Windings

“…Irregular edges of the winding cross-section and gaps within the conductor lay have been previously observed via X-ray and in sectioned machines [13], [16], [41]. The formation of irregular winding edges and gaps within the winding cross-section is expected to occur due to the conductors being 'dragged' against the slot wall during coil insertion into the stator.…”

“…Random winding conductor lay characteristics have been characterised using visual inspection [45], sectioning of windings [16], [41], colouring of conductors [48] and using Xray [13], [49]. Firstly, ground wall insulation, slot liners and slot wedges have been observed to lead to the triangular and rounded conductor formations at the slot opening and slot back respectively [13], [16], [41], [45].…”

“…Random winding conductor lay characteristics have been characterised using visual inspection [45], sectioning of windings [16], [41], colouring of conductors [48] and using Xray [13], [49]. Firstly, ground wall insulation, slot liners and slot wedges have been observed to lead to the triangular and rounded conductor formations at the slot opening and slot back respectively [13], [16], [41], [45]. The triangular formation of conductors is important to represent at the slot opening, due to the significant sensitivity of AC losses to the proximity and arrangement of conductors at the slot opening [3], [11].…”

“…As deviation away from a regular conductor lay will alter the conductor proximity and bundle losses, such characteristics must be incorporated into conductor lay simulations Finally, X-ray has shown that both the position of the winding cross-section within the stator slot, along with the proximity of conductors to the slot opening is highly variable, as shown in Fig. 9 [13]. In a similar manner to replicating triangular conductor formations at the slot opening, the variability in the proximity of conductors to the slot opening should also be accounted for in simulations to permit an accurate estimation of the AC loss variability [11], [39], [44].…”

“…1d, where the strands forming the bundle turns are more randomly mixed [12]. Further, strand transposition has been observed throughout the winding, with strands weaving along the slot active length and end winding [13]. Consequently, manufacturing processes lead to a conductor lay and strand positioning that varies from slot-to-slot and stator-to-stator, also known as a 'random winding' [4].…”