How to sizing a Kaplan turbine with HPP-Desing

 

What is a Kaplan turbine?

A Kaplan turbine is the most common type of propeller turbine, in which the angle of the blades and the gates to the flow can be adjusted. This type of turbine is most frequently used in the low- to moderate-head range and medium- to high- discharges.

 

When to use a Kaplan turbine

A Kaplan turbine can be used for heads ranging 2 to 50 m and discharges 1 to 100 m³/s (see the yellow line in the picture). Multiple turbines allow to increase the total discharge.

 

 

How to select a Kaplan turbine in HPP-design?

Just create a new sizing, enter a value of net head [H] and maximum discharge [Q] suitable for Kaplan turbines (e.g. H=20m, Q=10 m³/s), click “create sizing” and select the icon of the Kaplan turbine.

 

Why is not possible to select the Kaplan icon?

Check the values of net head [H] and maximum discharge [Q] you entered, probably they are out of the range of the Kaplan turbine ( H = 2 to 50 m and Q = 1 to 100 m³/s).

 

Why there are two numbers on the icon of Kaplan turbines?

The first refers to the number of available turbines without the gearbox while the second, if present, refers to the number of available turbines with the gearbox.

 

What is the “enable gearbox” switch?

When switched on it allows to use a gearbox between the turbine and the generator in order to better match the optimal speed of the turbine. The switch is enabled only for turbines with nominal power below a given value, when a low rotation speed is suggested for efficiency reasons. For high nominal powers a multiple pole generator is more effective and less expensive.

 

What is the “Suggested configuration”?

Is the optimal solution in terms of efficiency and it’s highlighted in green in the list.

 

Once I’ve selected the turbine on the list are there other possible options?

Yes, on the sizing-detail page you can choose the regulation strategy of the turbine and the type of generator.

 

How does the regulation strategy affects my turbine?

There are different possibilities concerning the regulation strategy:

·         Full Kaplan

·         Semi Kaplan rotor

·         Semi Kaplan stator

·         Helix

From the top to the bottom the equipment becomes cheaper while the efficiency at partial loads decreases, as you can see on the efficiency graph just below the sizing details.

 

How does the choice of generator affects my turbine?
For small powers only asynchronous generator are available, while for high power only synchronous are adopted. In between the user can choose a synchronous or asynchronous generator, the first one being capable of reactive power control and a bit more efficient, while more expensive than the second one.
 

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, or send us an email.

Doubts or questions? Read our [FAQ]

How to choose a hydroelectric turbine, a specific speed question!

The two main data needed to design a turbine are the maximum flow rate and the net head associated to this flow. However, these two values do not allow to uniquely define the type of turbine that must be designed; the designer is required to choose a third fundamental parameter: the number of revolutions.

Then it will be possible to define what we call the turbine specific speed.

But what is the specific speed? Leaving aside the theory about mechanical similarities, let's briefly explain what it is.

The specific speed of a turbine is defined as:

Where

    Q    maximum discharge     [m^3/s]

    H    net head  [m]

    g     gravity  (normal 9.806[m/s^2])

angular velocity of turbine [rad/s] calculated as:  

This parameter relates to each other the characteristic data of the turbine, and has the peculiarity of identifying families of geometrically similar machines (and then to scale them), having very different powers and sizes, but with one fundamental common characteristic: they are part of the only family of turbines that can process the available head and the discharge with the highest performance possible.

With simple calculations you can use the characteristic data of the turbine (H, Q and n) to find a value of specific speed  that uniquely identifies the most efficient type of turbine and its main dimensions. All this thanks to the experience gained in the design of more than a century of hydropower construction and excellent theoretical studies that have enabled the development of the theory of similarity at the basis of the specific speed calculations.

This does not mean that all turbines manufacturers build the same equipment once given the same typical number. After choosing the type of turbine and the main dimensions defined, each manufacturer has developed its own geometry and parameters that differentiate the turbines in terms of operation, reliability, cost and efficiency. Over the years, various design schools have proposed many definitions of the specific speed. The UNI-ISO has tried to standardize them into a single parameter, but in fact the definitions remain different.

In HPP-Design we use the parameter k, seen above, and nq

In the picture, every value of typical number of machine k (or nq) corresponds to a very specific type of turbine, exception made for some overlapping areas in which there is no univocal choice and the experience has shown that they can adapt well to different types of turbines (Pelton / Francis and Francis / Kaplan).

The question that arises is: how is this value really used?

Known the head and discharge, a preliminary study is made to define the appropriate number of revolution, taking into account some possible rotation speeds, and then calculating the relative specific speed which corresponds to a well-defined design solution. The possible solutions are then compared, in terms of performance, cavitation behaviour, main dimensions, etc.  and finally the choice is made for the solution that best suits the specific project. Once the rotation speed is fixed, starting from the specific speed it is possible to choose the type of turbine and start the detailed design.

Hpp-design is the tool that helps the designer to make a preliminary choice by comparing these elements directly into the chosen page. Try it out!

For information contact us here or send us an email here, you can also read the FAQs. Hpp-design is constantly updating and I recommend you to register to our newsletter here to keep up to date on new releases.