Projects : Generator Replacement Foundation Design; Consumers Power
(Cobb Station, Michigan)

The Consumers Power Cobb Unit 4 steam turbine-generator set is a 1950's vintage Westinghouse design. In recent years the generator had degraded to the extent that maintenance was becoming overly costly such that replacement became necessary. Even though modern machines are designed to match the existing plant duty conditions, the configurations of modern machines rarely match those of the older units. Consequently, modifications to the turbine pedestal concrete, isophase bus and auxiliary piping systems are required.

DPT performed structural analyses, developed designs and prepared construction plans and specifications to modify the turbine pedestal concrete so that a GE generator could be installed. While an important aspect of the modification was the design of new supports and analysis of turbine pedestal performance under operating and start-up loadings, the design focused on measures to minimize concrete demolition and the associated the cost and schedule for the modifications.

The new machine is 36 inches shorter and 22 inches wider than the original. DPT engineers worked with GE to optimize the position of the machine relative to the existing generator foundation opening and to match the existing power plant components. As shown in the figure, the final position selected required that GE provide a "jack-shaft" spacer between the turbine and generator couplings, but which minimized the amount of costly concrete demolition/reconstruction and provides for least-cost bus modifications.

To accommodate the different size and configured unit, significant modification of the foundation would be required, using traditional demolition/reconstruction means. because the new generator support feet are positioned wider than the existing support feet by about 11 inches. In order to minimize the amount of costly concrete demolition/reconstruction, DPT developed a unique adapter plate design that incorporates new drilled-in anchor bolts.

• Optimized generator position to minimize cost to modify concrete, isophase bus & auxiliary piping
• Design concrete modifications
• Design embedded adapter plate to accommodate anchor bolt mismatch and longitudinal anchors
• Design cooling water piping and seal-lube oil piping
• On-site engineering support