High dielectric performance stator winding insulation system for global VPI´ed air cooled generators

Stator winding insulation system for modern global vacuum impregnated (VPI´ed) air cooled generators are designed to perform under high electrical, mechanical, and thermal stress. Each component of insulation that goes into the fabrication of the stator coil is selected and tested to a very high standard so the stator winding will withstand these stresses over it´s intended lifetime. Operation of the stator winding in an air environment means the stator coil design must meet a very high standard of dielectric requirements. With the movement to increasing the power density of air-cooled generators, it has become more critical to be sure the design constraints are met in the stator coil design. Stator coil insulation stress factors are well known and for the most part understood and are taken into account when designing global VPI´ed air cooled generator stator windings. In addition to selection of the best available coil materials, special design considerations are incorporated into the stator coil to reduce internal and external coil corona. Significant advances have been made in the testing and analysis of coil materials prior to their use to ensure the coils are fabricated using the correct materials and to ensure the materials meet their original design parameters. In addition to the use of high performance coil materials and special design features, the global vacuum-pressure-impregnation equipment and process control are critical factors to insure the winding meets the stress factor demands. To verify final stator fabrication, impregnation, and proper cure, final testing of the completed stator winding includes power factor testing, corona inception testing and the standard AC high potential testing. This paper presents the major features of the stator insulation system used in the modern global VPI´ed air cooled generators and what measures are taken to be certain the completed stator winding will meet the high demands placed on it during generator operation.