Marshfield Turbine  Rehabilitation

Project Name: Marshfield Hydroelectric Plant Turbine Rehabilitation

Location: Colchester, VT

Project Size:       

Client: Green Mountain Power

Services: Plant Modernization, Penstock Evaluation 

Project Summary:

Green Mountain Power (GMP) completed a major overhaul on its Marshfield No. 6 Hydroelectric Plant.  The 350 ft. head plant, located on Molly’s Brook in Marshfield, Vermont, has an 8,300 ft long 6 ft diameter penstock leading to a 1927 vintage powerhouse. The single unit 5 MW station had to be shut down due to extreme turbine vibration. Kleinschmidt quickly responded to GMP’s urgent request for technical assistance. 

A dewatered inspection quickly revealed that the lower seal ring had become detached allowing high pressure water to bypass the runner, thus creating excessive cavitation damage. The loss of the seal ring, blade material, and balancing weights from the 1977 reconditioned bronze Francis runner contributed to the equipment vibration. Due to the condition of the existing runner and auxiliary equipment GMP elected to rehabilitate the station. 

Kleinschmidt subsequently prepared the work-scope and technical specifications for a complete system overhaul. After tender reviews GMP awarded the overhaul contract, scheduling re-installation just before the spring runoff. During the winter rehab, the wood stave penstock needed to be full to prevent wood stave shrinkage. Therefore Kleinschmidt calculated the bypass flow and thermal conditions required to prevent the stagnant penstock water from freezing.