How to sizing an Archimedean Screw turbine with HPP-Design

What is an Archimedean Screw Generator (ASG)?

An ASG is a positive displacement machine, which consists of a rotor in the shape of an Archimedean screw rotating in a semicircular trough. By filling the buckets of the screw, incoming water provides a tangential force, thus a torque, on the shaft of the turbine.

Thanks to its robust design, cheap construction, good efficiency, and tolerance to floating object transit, the ASG is a good solution for low heads and medium discharges.

When to use an ASG?

An ASG can be used for heads ranging from 1 to 5 m and discharges from 0.5 to 7 m³/s, as depicted by the red line in the picture below. Multiple ASGs are commonly used in side-by-side arrangement in order to increase the plant discharge, up to 30 m³/s (green area in the picture below).

How to select an Archimedean Screw Generator in HPP-design?

Just create a new sizing, enter a value of net head [H] and maximum discharge [Q] suitable for ASGs (e.g. H=3m, Q=5 m³/s), click “create sizing” and select the icon of the Archimedean Screw.

Why it is not possible to select the ASG icon?

Check the values of net head [H] and maximum discharge [Q] you entered, probably they are out of the range of the ASG (H = 1-5 m and Q = 0.5-30 m³/s)

Why there is more than one possible solution when I select ASG icon?

Because the required discharge can be achieved with different numbers of generators. More generators require more space and the cost of the plant is normally higher, nevertheless the single generator will be smaller and easier to transport, plant efficiency higher at partial loads and the maintenance easier.

What is the “Suggested configuration”?

Is the solution that allows minimizing the number of generator in the plant, thus the width and the total cost.

Why is there a limit in the maximum discharge of the single Archimedean screw?

Because of construction and transportation limits. Moreover, the lower the available head, the lower the maxim discharge per turbine due to aspect ratio constraints.

Once I have selected the turbine on the list, are there other possible options?

Yes, on the sizing-detail page, you can choose between a fixed-speed and a variable-speed regulation of the turbine. You will see a change in the part load efficiency on the graph.

Which turbine should I choose if both Kaplan and ASG are available?

What are pro and cons of an ASG as compared to a Kaplan turbine?

For heads between 2 and 7m, both a Kaplan turbine and an ASG are available. The first one has a slightly higher efficiency and smaller dimensions. On the other side, ASGs are frequently cheaper (lower CAPEX and OPEX), easier to inspect and allow the transit of debris without the needing of an automatic trash rack.

Through HPP-Design you can compare multiple solutions, check the features of each machine and ask for a quotation!

What is the expected efficiency of an ASG?

Despite its simple construction, an ASG is able to achieve hydraulic efficiencies over 80%. Main losses are related to hydraulic frictions, turbulence at intake and discharge section and water leakages between the screw and the through. Provided that water velocity in the screw is one order of magnitude lower then in reaction turbines, friction losses and kinetic energy loss at discharge are low.

How to regulate an ASG?

An ASG is rather different from traditional turbines, such as Kaplan, Francis or Pelton, since it is a positive displacement machine. Thus, it is regulated without the need of adjustable blades or gates. The screw self-adapt to the decreasing flowrate through a lower filling of the buckets and a lower water level at intake section.

A speed regulation through an inverter system allows achieving higher efficiencies at partial loads by keeping a constant level at intake section. 

Is an ASG reliable?

Although ASG is a relative newcomer to the hydro world, having only arrived on the scene over the last 25 years, they have been around for many centuries as pumps where tens-of-thousands unit have been installed worldwide, particularly in sewage treatment works. The same manufacturers that dominate the pump market are now the main suppliers into the hydropower market as well, providing reliable machines with very low operative costs.

HPP- Design will help you in this choice, providing accurate sizing data and energy calculation for every type of turbine!

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Doubts or questions? Read our [FAQ]

Hydraulic turbine range

 

This is the  range of application for the main hydraulic turbines. Have you seen how complex and overlapped it is? For a given head and discharge even three or more turbines could be suitable.

So how to choose the right one?

A good design should consider, alongside the nominal efficiency, the following aspects:

• Plant layout for the given location and layout related costs
• Annual average efficiency, matching the partial load efficiency curve with discharge and head variation over time
• Cost of the turbine and the mechanical equipment
• Operation and maintenance costs
• Water screen requirements as compared to the amount of debris carried by the river

By carefully considering all those aspects one can choose the optimal turbine and layout in order to maximize the energy and economic performance of the plant.

HPP- Design will help you in this choice, providing accurate sizing data and energy calculation for every type of turbine!
Need more information? You can follow us on Facebook, Twitter or send us an email.

Doubts or questions? Read our [FAQ]

 

 

A simple tool for Hydro Power Plants Design

Welcome to the HPP DESIGN BLOG

This is my blog, where I share information on HPP-design. I created this tool to help whoever wants to design a hydroelectric plant.

HPP-design is an automated tool to provide basic information on water turbines. It’s a very useful tool if you want to understand size, performance and specifications of hydroelectric turbines such as Pelton, Francis, Kaplan, Archimedes screw and Cross Flow. You can use it as a testing tool, for example to see if the size of the powerhouse is correct. Or if the assumed efficiency curve suits the turbine you chose. You can even try various hypotheses of turbine for the same installation, to determine which is the most appropriate range of operation to maximize production, dimensions and costs. All sizes will be saved online and you can access it whenever you want from any platform.

HPP-design has a simple interface and is very intuitive, to allow everyone work in the world of hydropower starting from its heart: the turbine.

In order to size a turbine we need two parameters: the net head (H) and the water flow rate (Q). To be more precise, we would also need the grid frequency (f). In Europe, f is normally 50HZ, but for more information take a look here.

With H, Q, and the frequency f, the tool displays a range of possible turbines. The variable data at this stage will be the fourth basic parameter for a hydroelectric turbine: the number of revolutions (n).

At this point, it is necessary to make a choice: the tool suggests a possible configuration, but the proper choice depends on the size of the plant, the price of the generator, the efficiency curve and other variables. If you are not experienced, choose the suggested configuration. Later I will explain the variables for the choice.

That’s it!. The tool shows main dimensions, data specification, and efficiency curve of the hydraulic turbine and some data for the generator’s configuration.

If you try to use the tool now, you will see that it only works for Pelton turbines and gives you several information that may be useful for a preliminary sizing of your power plant.

Please send feedback here. Information, suggestions and comments are welcome!