Document Yj8Zo3y6YD8xqqeoeEeaY1npE

Typical winding design oj a high-voltage machine. At right, the two coils in their slot position. At lejt, variouscoilcomponents appear in stages ofapplication. ,,7f WUW corering. i traction i he sucsoon re efs who of insu lt id con:il wcaklich had to be overcome. Some made an aboutface and applied mica tape along with vacuum and pressure impreg nation with an asphalt, emphasizing the importance of not only the selec- lion of material, but also the proper processing. An asphalt that is good ^enough to fill the fibers of cotton or {[asbestos in the internal part of a coil |(as was done early in this century) ay not be, and usually is not, suit able for application to the main high- ge insulation. This improper ction of a suitable impregnant has I some manufacturers consider: difficulty and field expense, beause it has been proved that straight phalts, so called, are not adequate 1 have not sufficient flexibility for * the type of operation encountered. In high-voltage coils, we have a number of turns, or conductors. Anv . piece of copper is known as a con ductor, but in the design engineer's V. 3 conductor and a turn are -tynonymous. A conductor consisting a "umber of parallel wires or -^strands combined is a turn. M About the >ear 1940 the transition which is taken for granted today, was a boon to the insulation designer. The use of glass-insulated strands within conductors not only gave better thermal insulation, but also a better space factor. It gave the de signer a chance to pack more kilo watts into a given machine. .As applied in the high-voltage machines this glass is only good as a spacer. It onlyreplaces cotton thermally and has no superior dielectric strength, so that mica must be placed on the turns. Even today there is no better highvoltage insulation than mica. After placing mica on the turns, the next step is to prepare the coil so that it is ready for application of the main high-voltage insulation. That preparation consists of molding the coil by treating it with a synthetic resin which polymerizes--that is, turns from a liquid to a solid, and does not soften upon any subsequent heating. It has made a chemical changesuch as you find with concrete. The coil, once molded to a pre determined size, is ready for the main insulation. Because of che shape of the coils, this molding is only ac complished in the slot portion and slightly beyond, in what is known as the straight portions of the coil. The same sort of treatment is impossible on the end-turns because of their shape. At this point the coils have been prepared for the main mica insula tion. This insulation is in the form of continuous layers and is known as Black Bond mica tape, a special Turbo-genrralar stator coils are here being molded to size by heat and pressure. PA(