First Hydro Company

Dinorwig Power Station

Dinorwig Power Station

When it was fully commissioned in 1984, Dinorwig Power Station was regarded as one of the world's most imaginative engineering and environmental project.

Today, Dinorwig's operational characteristics and dynamic response capability are still acknowledged the world over. Dinorwig is the largest scheme of its kind in Europe.

Dinorwig is comprised of 16km of underground tunnels, deep below Elidir mountain. Its construction required 1 million tonnes of concrete, 200,000 tonnes of cement and 4,500 tonnes of steel.

The station's six powerful generating units stand in Europe's largest man-made cavern. Adjacent to this lies the main inlet valve chamber housing the plant that regulates the flow of water through the turbines.

Dinorwig's reversible pump/turbines are capable of reaching maximum generation in less than 16 seconds. Using off-peak electricity the six units are reversed as pumps to transport water from the lower reservoir, back to Marchlyn Mawr.


Surge Pond Data:

Dimensions of surge pond 80x40x14 metres deep
Diameter of surge shaft 30 metres
Depth of surge shaft 65 metres


Type Vertical shaft, salient pole, air cooled
Generator rating 330 MVA
Motor rating 312 MVA
Terminal voltage 18kV
Excitation Thyristor rectifier
Starting equipment Static variable frequency

Generator-Motor Transformer:

Number Six
Approximate rating 340 MVA
Voltage ratio 18 kV/420 kV

Underground Caverns:

Distance of power station inside mountain 750 metres
Depth of turbine hall below top level of Llyn Peris 71 metres

Machine Hall:

Length 180 metres
Width 23 metres
Height 51 metres max

Transformer Hall:

Length 160 metres
Width 23 metres
Height 17 metres
Diversion tunnel length 2,208 metres
Width 6.5 metres
Height 5.5 metres
Maximum flow 60 cubic m/s
Normal flow 1-8 cubic m/s
Fall 1:1500


Type Reversible Francis
Number 6
Plant orientation Vertical spindle
Average pump power input 275 MW
Pumping period (full volume) 7 hours
Synchronous speed 500 rpm
Average full unit over all heads (declared capacity) 288 MW Generation potential at full load
Output 5 hours
Station power requirements when generating 12 MW
Standby operational mode
Synchronised and spinning-in-air emergency load pick-up rate from standby 0 to 1,320 MW in 12 seconds

Transmission Switchgear:

Type SF6 metal clad
Breaking capacity 35,000 MVA
Current rating 4,000 A
Voltage 420 kV


Main underground excavation 1 million cubic metres (approx. 3 million tonnes)
Total scheme excavations 12 million tonnes