You’ve been Screwed !

Headline caught your attention? Don't worry, we just wanted to grab you and tell you about a recent, project, so please read on. ITL has just completed another successful G59 commissioning project, this time for the Achranich Bridge Hydro Scheme, Ardornish Estate, Morvern.
 Our highly qualified engineers, predominately work on Wind Turbine & Photo Voltaic projects, the Archimedean Screw technology used in renewable energy generation is a first for us.
The Archimedean screw hydro turbine is a relative newcomer to the small-scale hydro world having only arrived on the scene over the last ten years. However, they have been around for many decades as pumps where tens-of-thousands have been installed worldwide, particularly in sewage treatment works. The same manufacturers that dominate the pump market are now the main suppliers into the hydro-power market as well.
As the name suggests, Archimedes is widely acknowledged as the inventor of the screw back in 250 BC, though the credit has been wrongly attributed because they were actually in use in Egypt many years before then. Historically they were used in irrigation to lift water to a higher level and were generally powered by oxen, or even humans on smaller versions. The basic principle of an Archimedean screw pump is shown in the diagram above. Basic-layout-of-an-Archimedean-screw-pumpIf the handle at the top was turned in an anti-clockwise direction it would draw the water up from the lower level to the top.
When used as a hydro turbine the principle is the same but acts in reverse. The water enters the screw at the top and the weight of the water pushes on the helical flights, allowing the water to fall to the lower level and causing the screw to rotate. This rotational energy can then be extracted by an electrical generator connected to the main shaft of the screw.
Archimedean screws for hydro-power are used on low head/high flow sites. They can work efficiently on heads as low as 1 metre, though are not generally used on heads less than 1.5 m (more for economic reasons than technical ones). Single screws can work on heads up to 8 metres, but above this multiple screws are generally used, though in many cases for
heads above 8 metres there may be more appropriate turbines available with much smaller footprints.

The maximum flow rate through an Archimedean screw is determined by the screw diameter. The smallest screws are just 1 metre diameter and can pass 250 litres/second, then they increase in 250 mm steps all of the way up to 5 metres in diameter with a maximum flow rate of around 14.5 m3/s. The 5 metre maximum is really based on practical delivery restrictions, and in many cases 3 metres is the maximum diameter that can be delivered to a site. If there is more flow available, multiple screws can be installed in parallel.

In terms of power output, the very smallest Archimedean screws can produce as little as 5 kW, and the largest 500 kW.

The main parts of an Archimedean screw used as a hydro generator are shown below. The actual screw is below the upper bearing. The helical screw or ‘flights’ are made from rolled flat steel plate that is then welded to a central steel core. Most Archimedean screws have three flights, or three separate helices winding around the central core.


Archimedean screws typically rotate at around 26 rpm, so the top of the screw connects to a gearbox to increase the rotational speed to between 750 and 1500 rpm to make it compatible with standard generators. Even though they rotate relatively slowly Archimedean screws can splash water around, though this is reduced significantly by the use of a splash guard shown running down the left-hand side of the screw as shown below.


ITL continues to work with contractors throughout the UK, commissioning & testing G59 as well as traditional switchgear Protection Relays from leading manufactures Schneider Electric, ABB, Siemens, CEE.

FP-g59 relay testing and commissioning