Volta River Authority (Ghana)

# Highlights

  • Reduced operating temperature from 83° celsius to 76° celsius.
  • PTFE bearing has one fifth the coefficient of friction, preventing excess heating of the thrust oil.
  • No additional cooling was required to lower thrust bearing temperature.
  • New thrust bearing supports 1132 imperial tons of thrust load.

# Facts

Location: Akosombo Generating Station, Volta River, Ghana
Type: Man-made Lake
Equipment: Six (6) 170MW Francis Umbrella Generators
Bearings Supplied: Six (6) Spring-Supported Thrust Bearings (PTFE)
Bearing Delivery: December 2009 - January 2011
Owner: Volta River Authority

# The Project

Background

The six generating units were commissioned in 1965 with an original installed capacity of 912MW. Having operated successfully for 30 years since inception, a major overhaul was carried out to upgrade and modernize the plant for an additional 25 to 30 years of trouble-free operation. Generation capacity was increased from 912MW to 1020MW however, recurrent thrust bearing damages were occurring which required frequent repairs and, in some severe cases, caused bearing failure. These failures were attributed to the turbine runner upgrades which had increased loading on the thrust bearings. Several attempts were made to correct the problem by modifying various parts of the thrust bearing with only partial, temporary success followed by eventual bearing failure.

 

Bearing design

Hydro Tech was contracted to design a reliable and permanent solution. The designed solution featured new and modified split thrust bearing rotating rings and superior Polytetrafluoroethylene (PTFE)  thrust pads providing higher load carrying capacity than traditional Babbitt bearings.

The new bearings have eighteen spring-supported bearing pads consisting of a PTFE surface with a steel backing plate supported by a bed of precision manufactured springs. The segmented runner plate is supported by a thrust block and held in place with radial keys and vertical bolts securing the runner plate to the thrust block. The runner plate segments are tightly bolted and keyed together, then machined to provide a solid, smooth and polished running surface. The new bearing design has reduced the operating temperature (to ambient) by 25 to 30% and increased thrust load capacity by more than 70%.