The Dinorwig power station


The Dinorwig power station was constructed in an abandoned slate quarry which was located deep inside the Elidir Fawr Mountain which has 6 massive pump turbines that are housed inside a man made cavern that is blasted out of 40 million years old Cambrian slate and from a standstill it takes just a minute for the pump turbines to produce 317MW each making a total of 1800MW.


The dinowig power station is a 1800MW pumped storage hydroelectric scheme that was commissioned in 1984 and was regarded as one of the world's most Imaginative engineering and environmental project, it was managed by First Hydro Company. The power station generates electricity using the principle of a simple water pump storage which requires two reservoirs at different altitude linked with a series of shafts and tunnels. In other to generate electricity, the water is released from Marchlyn Mawr i.e. the upper reservoir to Llyn Peris (the lower reservoir) and these water flows powers the generators. The Dinorwig power station has the ability to generate electricity depending on the volume of water available to power the engine in other to respond to the demand of electricity during the day. When the process for generating electricity ends, the water has to be pumped back to from Llyn Peris to Marchlyn Mawr at night when the demand for electricity is at the lowest.

2:History of Dinorwig power station

The history of the power station is dated back to the 1930s where there was an unsuccessful campaign to extend Dinorwig quarry. Dinorwig is a small village that has a long history of slate quarry located near Llanberis in Gwynedd, North Wales. The word Dinorwig means "fort of ordovices" because it was thought to be a part of the territory of the ordovice tribes. In the late 1770's until 1969, the slates from the valley are used by the Romans for construction until after the First World War where alternate roofing materials was available, the production and the used of these slates from the Valley declined and the people living there relocated to a nearby town. Today the village share its name with a pumped storage hydroelectric power station known as Dinorwig power station.

3:Construction of the power station

The dinorwig power station was constructed on an abandoned slate quarry located at deep inside the mountain Eldir fawr. The project was awarded by the Uk government to a British construction firm known as Alfred Mc Alpine and it took up to ten years to complete the construction of the power station because about 12 million tonnes of rocks were excavated inside the mountain creating tunnels and caverns of about 51m tall, 180m long and 23m wide known as "concert hall". The dinorwig power station is connected to the national grid substation at Pentir by a 400kv cables that are buried approximately 6 miles rather than use unsightly transmission towers to transmit electricity to the area with an outstanding natural beauty.

4:Environmental constraints at the site

During the construction of the site, the scientist ensure the protection of the welsh Arctic Charr, a native to Llyn Peris, a programme was devised to ensure the protection of these rare fish that are found in nearly four lakes in Wales to a safe location; a nearby glacial lake and they also ensure continuous monitory of the environmental issues such as the water quality and wildlife protection within the site. The architects and engineers find it difficult also in disposing approximately one million tonnes of rocks during construction and sites were chosen were the rocks could be dispersed and the contour of the local landscape; grasses, trees and shrubs were planted in order to improve and preserve the rich and varied natural life that surrounds the power station.

5:Detail description of operation.

The Dinorwig power station is a pump hydroelectric storage system that consists of one high reservoir and one low reservoir connected by tunnels containing generating plant, the water is released from the upper reservoir to the low reservoir through the turbines that drives the electric generators and when production exceed demand, the water is pumped back up to the upper reservoir ready to be released when needed. The power station uses more electricity to pump the water back than it generates on the way down and the pumping is usually done during the periods of low electricity demands and when the energy is cheaper to consume. Dinorwig comprises of 16km of underground tunnels, deep the Elidir Mountain with three main caverns

  • The main inlet valves gallery
  • The machine hall
  • The transformer hall.

The main inlet valve gallery at the upstream end links to the machine hall, whereas the transformer hall lies on the down stream end with the machine hall located below them.

5.1:The machine hall

Dinorwig machine hall was designed so that the pump/turbines will be sited below the level of the lower reservoir in other to minimise the damage to the turbine blade caused by entrapment of air bubbles, this machine hall houses six pump/turbines and generator motors; the control room, the low voltage switchgear, maintenance workshops and the power stations heating and ventilation systems. The machine hall has a length of 180m and a width of 24m and a height of 51m.

5.2The transformer hall

The transformer hall contains the massive transformer which converts the 18,000 volts current produced by the generator to the required voltage for transmission through the national grid which is usually 400,000 volts. The transformer are connected to the metal-clad switchgear on the floor above with a height of about 17m,a width of 23m and a length of 160m.

5.3:The control room

This is located within the machine hall and is the centre of all system management and operation, it controls each generating unit, programming the 300 individual steps that guide each from shutdown to full power output. The operations here are usually in contact with the national grid and a single operation can supervise the whole six units of the turbines.

5.4:The Hydraulic system

During the generating process, the system has to accelerate the 2km water column from standstill to full flow in just 11 seconds as well as dealing with a maximum demand of 390 cubic metres of water per seconds through the inlet valves providing sustained and reliable electricity output.

5.5:The surge pond

Its major function is to act as a safety valve when the generation process is complete and the inlet valve closes. The surge pond also provides reserve water for the high pressure effect as the generation starts.

5.6:Main inlet valves

This houses all six inlets valves and these Hugh construction controls the flow of water into the station to drive the turbines. The valve can be opened to 50% capacity within 5 seconds releasing up to 65m3 of water per seconds into the turbine system, inside each valve there is a huge ball mechanism which open and closes by two 16 tonne hydraulic counter weight arms. The inlet valves have been constructed to withstand the extreme forces and pressure of large water; it takes about 20 seconds for the valve to close.

5.7: The pump/turbines

Here the water that passes through the in-let valve at high pressure is directed to the turbine runners which is the moving part of the turbine and is essentially a horizontal water wheel connected to the turbine's central shaft. The force of the water that passes through rotates the shaft at 500rpm in a clockwise direction to the power of the generator and when this generator is run as a motor to reverse the rotation of the shaft, the unit act as a pump to transport water from Llyn Peris back to Marchlyn Marr.

5.8:The generator motors

The Dinorwig generator motor is coupled to the pump using a central shaft and this generator is magnetic rotor which spins within a circular stator, the electricity is created through the electromagnetic induction principle. During the operation of the system, the air coolers regulate the temperature of each unit which has been built with mechanical and electrical braking systems and electronic governors to control generating and pumping. At Dinorwig power station, the generating units stand vertically to make efficient use of space, each rotor weighing 445 tonnes. The generator motors are connected to a complex network of bus bar within the transformer hall which steps up the voltage for transmission using the underground cables to pertir station. The electricity that is fed to the national grid is from the generator motor.


The Dinorwig power station is enhanced by the fast response of the spinning air function which allows each of the turbines to work fast during operation. In its stationary mode the turbine are immersed to the water and since the generator is placed on standby, compressed air is injected into the turbine thereby displacing the water. The generator and the spinning-in-air are brought together using a very small amount of electricity and when instruction is received from the national grid to start generating almost immediately where the inlet valves opens and closes within five seconds as the water flows take over thereby producing electricity. This process reduces the amount of energy required to keep the turbines on a standby mode.

5.10:Dinorwig dams

Dinorwig power station comprises of two dams namely;

  • Marchly dam
  • Afor -y-Bala dam

6.0: Principle for operating generator motors and pumps turbines

The principle under which Dinorwig power station works is when two large volume of water are stored in the reservoir at different altitude, the water is then released from the top reservoir creating energy that will be used to drive the turbine which in turn powers the generator to create electricity. The water that is captured from the lower reservoir is then pumped back to the upper reservoir through the pumped shaft to the turbine shaft using a pump motor that is powered by electricity from the national grid. The water that is pumped back will be stored in the upper reservoir.

The cross-section of the Dinorwig power station scheme. During the operation, the water is released through the head gate into the concrete-line low pressure tunnel system and as the down flow reaches the surge shaft, it then pumps up to 568m before entering the high pressure tunnel system which splits into 6 separates and narrow steel-lined penstocks which then directs the water through the inlet valves and to the turbines. All the turbines are connected to their own generator and as soon as the shaft rotates the generator huge central rotor, which spins within a stator to produce electricity. This electricity produced is increased to 400,000 volts by a transformer network before it is connected to the 400kv cables about 11km underground to the national grid.

7.0 Dinorwig role in supplying electricity to the national grid

In England and Wales most of the electricity distributed to the country is by a network of power lines owned and controlled by the national grid and it their responsibility to ensure that electricity is available anytime needed. The Dinorwig power station has the ability to respond quickly to the national demand for electricity and is very important to balance the electricity supply in the UK. Since the demand for electricity is usually needed throughout the day because less power is used at night, in other to match this variation in demand, Dinorwig power station store the excess electricity generated at night to be used during the day and by so doing the plant can supply electricity to the national Grid and the power fed from the Grid can be used to recharge the reservoirs. In the "UK Energy Review" there are significant long-term increase in Renewable energy such as wind and there will be need for a reserve and Dinorwig power station has the largest flexible electricity producing equipment in the UK and will play an important role in supporting the national grid.

8.0:The economics of operating the power station

The economics includes the total costing of the project which is about 425 million and it took about ten years to complete the building of the entire site and also the electricity needed to pump the water from the upper reservoir to the lower reservoir is been paid though it is usually bought at a cheaper rate from the grid during off-peak hours and is sold back to the national grid during the day, thereby making some profits in running the power station. Some other cost includes the recreational developments of the area, maintaining of the water quality for the preservation of this historical site and protecting the aquatic/wildlife within the station.


Energy plays a vital role in our modern economy of which this energy system faces new challenges in trying to meet up the target of the Uk policy and legislation of white paper in creating low carbon economy by 2020 i.e. 20% renewable energy. The Dinorwig power station emits carbon dioxide when water is being pumped during off peak hours thereby producing less carbon dioxide compare to other power generating sources.


Directorate-General for energy and transport (2009) Legislation U k-energy white paper: our energy future-creating a low carbon economy [online] Available: (accessed December 10 2009)

The dinorwig slate quarry (2009) [online] Available: (accessed December 8 2009) e-hall-small_blog.jpg

University of Glamorgan - Prifysgol Morgannwg

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