Results / Turbine design for variable speed operations

Design and optimization of the runner in Francis- turbines

HydroCen researcher Igor Iliev has designed a turbine that can change gears. It can be used in new and upgraded hydropower plants to ensure more variable operation and is an important step to ensure a stable power supply in a renewable energy system with both water, wind, and solar energy.

Design and optimization of the runner in Francis- turbines

The PhDs Gro, Igor and Johannes are studying turbines at NTNU's Hydropower Lab.
The enormous forces of water rushing through the tunnel and into Norwegian hydropower plants are almost 100 percent utilized to produce power. Only 4-6 percent of the energy in the water is wasted when it passes through a Francis turbine. It has worked perfectly for a hundred years, but climate change is leading to both more unstable weather conditions and cuts in fossil energy sources. This means that hydropower must now operate in a new way.
Conventional water turbines are designed to operate continuously at a fixed speed to produce an expected amount of electricity for the grid. When today's hydropower is to function more like a green battery that is switched on and off depending on how much solar and wind energy is produced, the turbine faces a major challenge.
It performs less well when exposed to water volumes greater and less than it was designed for. This leads both to energy/power production becoming less efficient and to increased wear and tear on the turbine parts. This wear and tear leads to expensive repairs and can lead to reduced confidence in the power plant, which then cannot deliver the services needed when they are needed. One solution to this is to provide turbines and generators that can operate just as well at variable speeds as current technology does at constant speeds.

FACTS ABOUT FRANCIS

The Francis turbine has been the most used turbine type in Norway in recent years, partly because of its simplicity.
Designed by the English engineer James B. Francis in 1894.
It is more like a paddle wheel than a propeller in design.
Further developed at, among others, the Hydropower Laboratory at NTNU (NTH).
Can be adapted to large and small hydropower plants but is most common with drop heights from 30 to 70 metres.
The water is led onto the turbine wheel through a spiral tube (spiral drum).
Directly before the turbine, there are guide vanes that can regulate the amount of water and thus also the speed of the turbine.

Old ideas in new guise

Although the idea of using variable speeds/speeds is not entirely new, it has become more relevant today when you can earn more by being flexible. In addition, it has been realized that turbines designed for constant speed do not work optimally when they are operated at variable speeds, so new designs and methods are therefore needed to increase efficiency. This is where Igor Iliev comes in.
In his PhD project, based on the Francis turbine model, he looked at the possibility of improving the design of the runner of the turbine. The runner is the turbine part that experiences the most losses when operating at non-design speeds. He created an algorithm that simulated various possible changes for optimal design of the runner to find the full potential of the turbine if it were to be operated almost exclusively at variable speeds.

Recommends new turbine design upgrading and new hydropower plants

The results from the project show that there are designs and modifications to the Francis turbine that can make it better adapted to operate at variable speeds. These modifications will be individually dependent on the power plants they will operate in but are recommended when building new - and when upgrading old power plants for the most flexible and optimal energy production possible at variable speeds.

The figure shows a comparison between the reference design for the Francis turbine (left) and the optimal design for variable speed (right).

FACTS ABOUT THE DESIGN

The figure describes the driving pattern with variable speed which has maximum efficiency, where speed variation is used to balance the dominant partial losses in the turbine. Watch Igor explain this in the GodForskerMorgen webinar.

Using traditional and new methods, Igor has produced hundreds of digital simulations of the runner to find the optimal design for variable speed. What he found was that the main dimension of the impeller in the turbine is what determines how well the turbine performs, while the turbine blade design was what retained the full potential of the turbine at variable speeds.

Do you want to know more about the design? Read Igor's doctoral thesis HERE.