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.
Article Source: Renewables First (click to read full article)