Generator upgrade without stator rewinding

It can be expected that a hydrogenerator stator winding may require replacement when a machine is upgraded more than 25%. A case study is presented where detailed thermal and electrical analysis was performed on spare stator coils purchased when the stator winding of a 158 MVA machine was last rewound in 1988. Results of these accelerated aging tests indicated that continued safe operation of the existing ten-year-old stator coils with an expected turbine upgrade of 27% was possible. Capability tests conducted since the upgrade indicate temperature limitations for the existing insulation system will not be exceeded during normal operation at 200 MVA. Results of thermal and electrical aging tests are presented.