  There is currently a major trend to hairpin-winding motors for small and
medium drives with increased power, specifically more torque density in the
automotive industry. Practically all large players in the field either already
use this winding technology or have announced doing so soon. However, hairpins,
bar windings, and other segmented winding techniques are not purely a material
and production issue. Instead their application to small drives influences all
aspects of the design of machines, which are currently explored and studied by
the industry. These range from not obvious gaps in the theory, parameter
studies for maxima of efficiency, possible as well as advantageous winding
schemes, thermal design, and ways to control ac losses to specific materials
and process difficulties. Despite the apparent novelty of the trend, however,
designers could revisit a widely forgotten knowledge base of more than 100
years for many of those questions. This old knowledge base and the
understanding that many recently presented concepts have been developed earlier
may speed up the technological development and appear to be a key to further
innovation. Instead, many problems need to be solved again and technologies
re-invented. Furthermore, as this technology has recently become merely
industry-driven, a substantial portion of the information and technological
developments are not available to the public -- a state that to our eyes may
harm the innovation capacity of the drives community.
