Chain or Basket Winding.—One disadvantage in ordinary two-range windings is that two or three separate shapes of coil are required. The cost of making, winding, and supplying spares would be less if one shape of coil could be made to do for all phases. One way of accomplishing this is by the method of chain winding, in which the two sides of each coil are made of different lengths, as shown in fig. 1,563, and bent so that they can lie behind one another.
Fig. 1,563.—Diagram showing chain winding. In this method of winding the coils are all similar with long and short sides. It obviates the extra cost of making coils of several different shapes. The diagram represents a winding for one slot per pole per phase.
Fig. 1,564.—General Electric terminal board showing cables leading to three phase winding.
In the case of open slots the coils may be former wound and afterwards wedged into their places.
In chain winding the adjacent coils link one another as in a chain (hence, the name); the winding is similar to a skew coil winding. This plan of winding is supposed to have some advantage in keeping coils of different phases further separated than the two range plan.
Fig. 1,565.—Section of armature winding of Allis-Chalmers 500 kw. three phase water wheel alternator. The coils are of the concentrated "half" type. Each coil is completely insulated before being placed on the core and no insulation is placed in the slot itself. The ends of the coils where they project beyond the slots are heavily taped. Where necessary suitable supports are provided for the coil connections so that they cannot become displaced on account of stresses due to short circuits or other causes. The winding is of the "chain" type. This is shown by the way the coils are connected together at the right. The armature terminals are either provided with insulated connectors or are led to a marble terminal board on which the terminals are so mounted and protected that it is impossible for an attendant to make accidental contact with them. The position of the illustration would indicate a horizontal alternator but the machine is of the vertical type; the lug on the right shows this, being used for adjusting the alternator on the foundation.