Preventing a major in-service failure of Pioneer Mill STG 3 stator core and winding

During a routine inspection of the Pioneer STG3 46 MVA Generator, serious issues with overheating of the inter-strand insulation on the transposition coils were identified. Due to the criticality of this generator to cogeneration operations, the complexity and time associated with either a rewind or a complete replacement of the generator, the decision was made to replace the stator core and winding only as a complete unit. Due to the unique design of this generator the removal of the old stator core and installation of the new stator core and winding could be undertaken in a relatively short period. This was important in this project, since the available time-window allowed by the production schedule to work on the generator was very restricted. A stator rewind and possible core re-stack in the conventional sense would not have been possible for this generator due to this limited time-window and available winding data. Total replacement of the stator core and winding was, therefore, the only feasible option to meet business needs. This replacement strategy would allow the generator to remain in service, after minor repairs, until April/May of 2019, where an optimal cogeneration window was identified for Siemens to install the newly manufactured stator core and winding. To meet the tight timelines required, the new stator core and winding were manufactured in Germany and air freighted to Australia. The project activities were all completed within the planned schedule and final commissioning and testing proved that the generator performance was as expected per design specifications. Key words Pioneer STG 3 46 MVA generator, stator core winding, Siemens