ESB Logo

To view this presentation, you will need to upgrade your browser to a modern version for security and performance improvements. Visit Browse Happy to find out more.

If you are using a legacy version of Internet Explorer, please also ensure that 'Compatibility Mode' is turned off.

 

To view this website, please turn your device around into 'landscape' mode.

ESB Logo

Unfortunately you cannot view the presentation unless your browser window is 1024 x 700 pixels or bigger in size. Please try resizing your browser or using a bigger screen.

You may also try adjusting the 'zoom' value to 90% or less if your browser supports this feature, but please be aware that this will reduce the visual clarity of the presentation.

 
Water from
Main Inlet Valve
 
Coupling Shaft
 
Inlet Guide Vanes
 
Pump Turbine Blades

The Cavern

Pump Turbine Unit

The water strikes the Turbine blades causing the shaft to rotate at 500 revolutions per minute.

Inlet Guide Vanes are adjustable, and used to regulate the flow of water thus controlling the blade speed and therefore power output.

  • What is a Turbine?

    A turbine is a mechanical device which rotates under the influence of a flowing fluid. It converts the kinetic energy of fluids into useful work.

    The technology used here is known as a Francis Turbine. It is by far the most popular type of pump that is used in hydroelectric stations around the world. It is, in fact, used in the generation of about 60% of the world’s hydropower. This turbine operates with an efficiency of about 88%.

  • The Turbine in Detail (1 of 2)

    When the valve (akin to a domestic tap) is fully open the fast flowing water can travel the final short straight towards the inlet nozzle on the spiral casing (that resembles a snail shell) of the Pump Turbine. The spiral case is a circular pipe that gradually decreases in diameter along the flow path. It is widest at the entry point and far narrower at the exit.

    There is a very specific reason why the pipe narrows and this is to keep the flow rate of the water at a constant speed. The steady flow rate is essential in order that each blade on the 'runner' is hit by the same force from the water. This allows the runner to rotate smoothly and it avoids jumping or stalling of the instrument. This is similar to how a keen rower knows that each blade of their oars must be doing an equal amount of work in the water for the boat to move fluidly.

  • The Turbine in Detail (2 of 2)

    While the water travels around the external circumference of the runner the fluid is drawn inwards through openings in the structure. On its own this would cause the flow of the water to steadily decrease if the width of the pipe was uniform. But the engineers know that fluids increase their velocity when traveling along a narrowing pipe. This is why a petrol funnel does not overflow when you are filling up your lawnmower. The flow rate increases as the funnel narrows - helping to avoid an overflow when you are pouring in the fuel. In the case of the Pump Turbine the narrowing diameter is a counterbalance to the influence of the runner.

    The water enters the runner radially (along all parts of the circumference) but it exits the runner axially as it free falls vertically away from the runner. The guide vanes are moveable, and within the turbine they are used to control the rate of flow which in turn controls the electrical output of the station. The station does not have to operate at full capacity every time the intake gate is opened.

  • Continuity of Water Flow Rate

    If a fluid is travelling along a pipe where the diameter is changing then it will speed up or slow down depending on the degree of change. This is to ensure that the pipe doesn't burst or back up. This idea is known as the Continuity of Flow.

    In summary, the product of fluid velocity and a pipe's cross sectional area is a constant. This is why water sprays out of a hose when you cover some of the front section with your thumb. The water speeds up so as to pass the full volume of fluid travelling in the hose.

The Cavern - Pump Turbine Unit