Conversion of a GE 7FA From 60 Cycle to 50 Cycle Generation

This paper examines the conversion of a GE 7FA from generating 60 Cycle power to 50 Cycle power. The turbine is nominally rated for a 60-cycle ISO output of 175 MW. With the gas turbine boom of the late 1990s and then the cancellation of several GT based projects, a surplus of GTs has been created. Owners of these GTs have been reviewing alternative options for installation at another of their plants or resale of their GTs to another user. One potential solution is the conversion of a GT into a 50-cycle machine for installation in other markets around the world. If this type of conversion proves feasible, it also opens the door for the 60-cycle designed GTs to be marketed overseas to compete with original 50-cycle equipment. Three potential options for creating 50 Cycle power with a 7FA were identified: 1. Operate the Combustion Turbine Generator (CTG) at 3000 RPM to generate energy at 50 Hz. 2. Operate the CTG at 3600 RPM to generate energy at 60 Hz with the installation of an invertor, external to the CTG, to convert 60 Hz potential to 50 Hz. 3. Operate the turbine at 3600 RPM and the generator at 3000 RPM by installing a gearbox (speed reducer) between the turbine and the generator. These three options were researched and pricing was obtained on those that were considered feasible. The turbine OEM, GE, was also contacted to provide input on each of the scenarios. The results for each of the options are as follows.