Bureau of Reclamation guidelines regarding high-voltage rotating machine stator winding procurement, installation, and maintenance procedures

The first installations of the new hard epoxy-mica or polyester-mica stator insulation systems in Bureau of Reclamation generators resulted in numerous problems that were not present with the older soft asphalt-mica systems. One of the main attributes of asphalt-mica systems was the tendency for these materials to expand and lock themselves into the stator slots. When the asphalt becomes warm and somewhat plastic, it flows and causes the coil surface to bulge into the air passage slots. Because the binders in the hard systems remain rigid, the coils must be secured in the slots by other means to prevent movement. In the early years of hard insulation system development, loose coils became the major operation and maintenance concern. Many windings wore out prematurely due to severe electrical and mechanical deterioration resulting from loosely installed coils. A factor causing looseness in the slots involves further curing of some insulation systems after installation, resulting in volumetric shrinkage of the insulation. Manufacturers have addressed this problem by developing coil-clamping systems that maintain slot pressures regardless of volumetric shrinkage. The Bureau of Reclamation has developed maintenance procedures to detect loose coils and correct the situation before serious damage occurs. Some case histories involving the new hard winding insulation systems are presented