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“Coil Forming: More than Simple Geometry" With
trilingual summary
In ratings above 600 volts, most polyphase motor
and generator stator coils originate with loops of rectangular
conductor bound into a rectangular shape that is then spread into a
diamond configuration. The two straight sides are positioned into
lamination slots separated by the coil width (pitch).
Size and spacing of the pins on which the loop is
wound are determined by the coil's complex geometry, involving
clearances needed between adjacent coils, to the stator bore
diameter, and to the enclosing machine frame.
Spacing between coils must allow passage of
ventilating air and for bracing against electromagnetic forces. Also,
the clearance must allow for the sliding of one coil past another as
they are wound into the stator. Without careful design, that
clearance may disappear gradually during winding, so that the last
coils to be inserted become blocked. That can require removal and
re-shaping ofthe entire set.
Because the coil side in the bottom of one slot
lies on a circle of larger diameter than the coil side in the top of
its slot, that bottom side is inherently the longer of the two.
However, the length of conductor is the same in both, so that their
junction point is necessarily shifted toward the bottom side during
spreading. That reduces the top side clearance. One shaping option
used to offset that is twisting the end of the loop through an anglem
as the coil is spread, shortening the length of both sides and
opening up the top side clearance. Another choice for the designer is
adding two more pins to the looping process to place more conductor
length in the bottom coil side.
Such modifications, as well as the compound
curvature naturally formed into the spread coil, and the influence of
the tooling used in coil spreading, must be properly accounted for in
the design process so that the initial loop will be of the proper
length.
From “The
Coil Forming: More than Simple Geometry" to
be published in Electrical Apparatus
November 2006
. Visit our online webstore to
order a
copy. © 2006
Barks Publications, Inc. All Rights Reserved.
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