spear valve and maximum power output

[ThomasS]

Question: 

The available water flow varies greatly. A spear valve needs to be adjusted according to the available water, in order to always achieve the maximum possible power output (= maximum efficiency, best use of the available water).

If possible, we want to avoid a water level sensor at the water intake, because it means additional cabling and equipment.

The valve should be controlled automatically for maximum power output.

Solution:

A microcontroller which measures the output amperes of the generator, and possibly also the water pressure before the valve.

The spear valve can be moved with a stepper motor or a gear motor.

The microcontroller controls the motor.

The software algorithm follows this procedure:

Measure the amperes, turn the spear valve and observe if the ampere decrease or increase. Now it knows the direction it needs to turn. Then it keeps turning, until the ampere decreases again. Then it turns back to the maximum ampere point. This is your maximum power output.

 

If you do a series of test measurements at different flows, and enter

- the maximum power output (= ampere) at any given flow

- and the corresponding pressure just before the valve

 

into a diagram, then you will get a correlation, which will depend on the kind of turbine and the shape of the spear valve which you are using.

 

If you have an electric pressure sensor, then you can use this pressure graph to improve the effectiveness of the software adjusting algorithm. E.g. if the pressure rises aboe the graph without a change in ampere output, then it's time to open the valve a bit again.

 

Make sure that the generator output voltage is constant for all the measurements, so you get valid results.

The correct adjustment of the spear valve is especially important with pelton turbines.

Crossflow turbines generally can maintain a good degree of efficiency over a wider range of water flows than pelton turbines.

If you need to manage a really wide range of water flow, consider using a small and a big turbine on one axle.