Electrical Apparatus magazine, November 2006 Coil Forming: More than Simple Geometry

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.

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Featured Technical Article
November 2006

On this page is a summary of the Electrical Apparatus November 2006 featured technical article, by Richard L. Nailen, P.E. , "Coil Forming: More than Simple Geometry" Bildung von Wicklungen; mehr als simple Geometrie ... Mise en forme des bobines: Plus qu'une simple question de géométrie ... Formación de Bobinas: Más que una sencilla cuestión de geometria ..

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