City of Sitka, Alaska
The City of Sitka is situated on the west side of Baranof island in the southeast panhandle of Alaska. Sitka receives almost three times more rain than Seattle and this water is used in two hydro electric power plants to supply 100% of the required electricity to the town. In recent years, Sitka has experienced load growth due to rising oil prices and as the oil prices continue to rise, the small island town of approx. 10,000 residents, relies more on electric heat.
The two existing Blue Lake hydro power turbines would no longer supply enough power to the city and additional power sources were explored. To satisfy the additional and future power requirements of the city it was decided that a new, larger hydro power scheme would be installed to replace the existing two units.
In 2010 Gilkes were awarded the contract to supply the new turbines and associated equipment. Primarily the arrangement would be 3 x 7.140 MW Francis units but also a smaller 1625 kW Francis unit would be installed to utilise the water that must be pumped into the river down from the Blue Lake dam to conserve the Salmon population.
The project was reliant on a vast civil project that was undertaken by the City. The height of the dam had to be increased by 83’, there was to be a new power house, new intake, new penstock and new surge chamber.
To aid efficiency, Gilkes upgraded the runner design as well as increasing the number of segments that made up the turbine case.
Commercial operation started November 2014 and since then the units have exceeded their guaranteed average efficiency value by over 4%.
Scope of supply
• 3 x 1050mm G150 Francis reaction turbines fitted with hydraulic actuators
• 3 x Set of inlet pipework up to the flange of the main inlet valve
• 3 x Main inlet valve, double flanged 1400mm butterfly valve, weight to close hydraulic actuator
• 3 x Weld prepped Inlet Pipe upstream of MIV
• 3 x 9511 kVA Synchronous Generator
• Individual control panels, Individual hydraulic power units
• Individual cooling water and pressure sensing panels
• Full set of O&M manuals
• Additional ‘Fish Valve Unit’ 1625 kW Francis Turbine
DOWNLOAD FULL CASE STUDY
- Commissioned 2014
- Power (kW) 7.140 MW Each
- Net Head 356 ft
- Flow 255 cfs
- Turbine Type Francis G150