Rewind and Core Restack of AEP Conesville #5 Generator

This paper presents an overview of the design and field installation events involved in rewinding and restacking AEP’s Conesville #5 generator. This style of generator, commonly known as a “double tube stack” machine, has been susceptible in the past to stator end winding vibration, stator coil and core deterioration, and phase lead problems. Following tests and inspections, AEP decided to rewind this generator in anticipation of the consequences of these problems. Successful pro-active maintenance, which included a complete stator rewind and stator core restack, prevented a costly forced outage. Root cause analysis of the coil failures are described, as well as details of the core laminations problems. Specific design enhancements over and above the original design will be discussed. In addition, details of the existing core damage will be discussed, as well as procedures used for core restacking. Fiber optic monitoring instruments were installed on the coil ends and the phase leads after the new coil installation was complete. Results of these initial readings will be shared. Successful startup and continued operation of this unit demonstrates that refurbishment of these large generators with inner gas cooled technology is reliable and cost-effective over other alternatives, such as conversion to water cooled technology.