First Hydro Company
Ffestiniog Power Station
Commissioned in 1963, Ffestiniog Power Station was the UK's first major pumped storage power facility. Although of an older generation to those at Dinorwig, Ffestiniog's four generating units are still capable of achieving a combined output of 360MW of electricity - enough to supply the entire power needs of North Wales for several hours.
The Generation Cycle begins at Llyn Stwlan - Ffestiniog's upper reservoir. Large screens inside the intake towers are opened to activate the high-pressure downflow.
27 cubic metres of water per second are discharged through two high-pressure shafts (each 200 metres in depth), which are connected to four concrete-lined tunnels. Steel penstocks then direct the discharge into the station via inlet pipes and valves to start generation.
Water is captured in Tan-y-Grisiau and pumped back to Llyn Stwlan, usually overnight, to complete the cycle.
FFESTINIOG FACTS & FIGURES (STWLAN DAM & RESERVIOR)
Dam: |
|
| Type | Massive buttress gravity |
| Material | Mass concrete Total |
| Length including spillway | 373.4m |
| Maximum height of dam above foundations | 34m |
| Maximum thickness | 4m |
Reservoir: |
|
| Designed live storage | 2 million cu metres |
| Designed maximum operating above water level | 502.4m ordnance datum |
| Designed minimum operating above water level | 482.5m ordnance datum |
| Average annual rainfall | 3m |
| Catchment area | 65 hectares |
Pressure Shafts, Tunnels and Pipelines Intakes: |
|
| Number of intakes | Two |
| Number of intake towers/intake | Two |
Vertical Shafts and Tunnels: |
|
| Number of shafts | Two |
| Depth | 195m |
| Internal diameter | 4.4m |
| Lining | Concrete |
| Number of tunnels | Four |
| Internal diameter of steel pipe linings | 2.8m |
| Gradient of tunnels | 1 in 40 |
Pipelines: |
|
| Number of pipelines | Four |
| Length of each pipeline | 213m |
| Thickness and material | From 22m to 26m |
| Coltuf 32 steel internal diameter | 2.3m |
Tan-y-Grisiau and Reservoir: |
|
| Dam type | Gravity |
| Material | Mass concrete |
| Length including spillway | 549m |
| Length of spillway | 79m |
| Maximum height of dam above foundations | 12.2m |
Reservoir: |
|
| Designed live storage | 2 million cu metres |
| Designed maximum operating above water level | 187.9m ordnance datum |
| Designed minimum operating above water level | 182.3m ordnance datum |
| Average annual rainfall over catchment area | 2.2m |
| Catchment area including that for Stwlan reservoir | 951 hectares |
Power Station Plant Generator/Motors: |
|
| Number | Four |
| Rating as generator | 90 MW at 0.95 PF |
| Rating as motor | 75 MW at unity PF |
| Output as motor at 50 cycles/second | 104,000 bhp |
| Speed | 428 rpm |
| Rated voltage | 16 kV |
| Cooling system | Closed circuit air cooled with air/water heat exchangers |
Excitor Main: |
|
| Speed | 428 rpm |
| Drive | Direct |
| Rated Voltage | 181 |
| Rated current | 1050 |
Turbines: |
|
| Number | Four |
| Type | Vertical shaft reaction |
| Design Net head | 296m |
| Discharge at design net head and maximum efficiency | 29 cu metres/sec |
| Speed | 428 rpm |
Turbine Inlet Valve: |
|
| Operation | Hydraulic servomotor |
| Inlet diameter | 1.8m |
| Opening time | 60 seconds |
| Closing time | 60 seconds |
| Weight | 86.3 tonnes |
| Spiral casing construction | Welded plate |
| Number of guide vanes | 24 |
Runner: |
|
| Construction | Cast stainless steel |
| Exit diameter | 1.8m |
| Number of vanes | 13 Storage |
Pumps: |
|
| Number | Four |
| Type | Vertical shaft centrifugal |
| Number of stages | Two |
| Number of inlets | Two |
| Design head | 305m |
| Discharge at design head | 22 cu m/sec |
| Power required at coupling at rated discharge | 93,600 bhp |
| Speed | 428 rpm |
Pump Discharge Valve: |
|
| Type | Straightflow |
| Operation | Double hydraulic servometer |
| Outlet diameter | 2m |
Turbines: |
|
| Opening time | 60 seconds |
| Closing time (normal) | 60 seconds |
| Spiral casing construction | Welded plate |
Diameter of Impellers: |
|
| First stage | 2.4m |
| Second stage | 2.5m |
| Number of impeller blades | 10 each stage |
| Maximum diameter of shaft | 0.7m |
Generator Switchgear: |
|
| Type | SF6 circuit breaker |
| Breaking capacity | 174 MVA |
| Voltage between phases | 16 kV |
| Current rating | 6200 amps |
Generator Transformers: |
|
| Number | Two |
| Rating | 160 MVA |
| Ratio | 16 kV/275 kV |
| Cooling system | Water circulation from lower reservoir |
| Weight as delivered | 122 tonnes |
| Oil capacity | 27 cu m |
Auxiliary Transformers: |
|
| Number of station transformers | Two |
| Rating | 1 MVA |
| Ratio | 16 kV/415 V |
| Number of local supplies transformers | Two |
| Rating | 1 MVA |
| Ratio | 11 kV/415 V |
