Test Metrics and Damage Fingerprints in Multistranded Compressed Aluminium Windings

Aluminium coils in electrical machines offer a lightweight alternative to copper, with comparable resistance and reduced high frequency losses, especially when compressed. Conductor fill factors in compressed aluminium may exceed 70 percent, however the conductors and strand insulation are subject to mechanical stresses during the process and may be damaged. To screen out damaged coils and accept satisfactory ones with a quantifiable probability of success it is necessary to have clear, robust metrics and test criteria in place. This paper firstly identifies the tell-tale fingerprints of broken strands and turn to turn short circuits, which may be found using simple pre-assembly tests. Secondly, several test metrics are compared and statistical analyses are used to define tailorable criteria on which to accept or reject a coil to a given confidence level.