Rebuilding of the 70 years old Nore 1 Power Plant

摘要

At Nore 1 Power Plant the water was conducted from a low pressure head race tunnel to the above ground power house by 8 exposed penstocks of 1000 m length. For safety reasons, Norwegian authorities have ordered all so-called water gas welded penstocks to be taken out of service within certain time limits. A number of alternative schemes for the necessary rebuilding of Nore 1 were developed. The selected scheme was to replace the penstocks between the existing head race tunnel and the power house by a new underground waterway system in rock. Required rock overburden of water bearing tunnels and length of steel lined tunnel were determined by means of rock stress measurements as well as numerical analyses. Most of the tunnels were excavated by drill & blast while the power plant was in operation with the old penstocks. In the vicinity of the power house vibrations induced by blasting had to be kept within certain precalculated limits. To connect the low pressure head race tunnel to a new high pressure tunnel it was decided to excavate a vertical unlined pressure shaft of 213m length. However, the main challenge to the project was to limit outage time for the turbine units during the construction and erection period for the new system.