Influence of dielectric stress concentration on voltage endurance of epoxy-mica generator insulation

The structure and shape of the coils in high-voltage apparatus have a pronounced effect upon their electrical life expectancy because of the dielectric stress concentration at the edges and corners of the conductors. In these regions, as a result of the high dielectric stress, accelerated damage to the insulation can occur due to the partial discharges on the surfaces and in minute voids created during manufacture or in service. The extent of the influence of these increased stresses on the electrical life expectancy of several types of epoxy-mica insulation for large electrical machines was investigated.