Torque sensor monitors output of prototype tidal turbine

A small proportion of the Thames is to be illuminated using power generated by the flow of the river itself, as Kingston University tests prototypes of a new hydroelectric turbine design. The turbine will sit on a pontoon and provide a floating test and measurement laboratory. On this will be an array of sensors and monitors, including a TorqSense wireless torque sensor from Sensor Technology.

Rod Bromfield, Senior Lecturer, of the Faculty of Engineering, Kingston University, states: "To say that this is a harsh environment for laboratory equipment is a bit of an understatement. We can only use robust kit with a proven industrial pedigree."

The turbine under test has been developed by Hales Marine Energy near Eastbourne on the English south coast and is expected to be deployable in tidal seas as well as rivers. The design application of this turbine is to sit on a submerged tank on the sea bed, though it can be floated up to the surface when required. Significantly, the design is described as 'almost infinitely scalable': the unit under test is 1m diameter and produces about 1kW; 5m turbines suitable for inshore deployment would generate round 20kW; smaller units would be suitable for river use.

With access to the test site being by small boat, Bromfield knew that his test regime had to be both simple and comprehensive: "The critical measurement is torque, as this indicates the power we can derive from the system. We had to be certain that we would get continuous measurements over an extended period of time, because we need to map power production against actual river flow. Also for this technology to succeed in the emerging green power market it must be capable of continuous and predictable energy production."

One of the engineering issues that Bromfield faced was the relatively slow revolution of the turbine (below 50rpm in this test). This helped define the choice of the TorqSense, but it is also a key feature of the Hales turbine - the slow speed means less stress on moving parts and therefore less servicing. It also minimises habitat disturbance, so that the ecological impact is low. Torqsense transducers work using surface acoustic wave technology.

Bromfield comments: "When I contacted Sensor Technology I was very concerned about vertical mounting and harsh environment performance. Fortunately there have been TorqSenses installed vertically, including several high up on vertical-axis wind turbines, where they have to withstand gales, hurricanes and lashing rain."

Turbine design

The design of the Hales turbine is reassuringly simple, and therefore likely to survive underwater installation with long service intervals. It was developed by Paul Hales, a design engineer who has spent a career associated with the sea. he explains: "It is based on the traditional water wheel, but mounted on a vertical axis - on its side.

"Using modern engineering and materials it is possible to take this effective early turbine and by turning the output shaft to the vertical to immerse the whole turbine into the tidal flow. To overcome the high resistance on the wheel blades that on one side are trying to move against the water flow, they are shaped and hinged to present a minimum resistance. The large blade area on the drive side produces very high amounts of torque (rotational force) at low speed, in the range of 10-20rpm.

"Coupled with modern permanent-magnet generators that can start producing electricity rotations as low as 2rpm, my turbine can offer the possibility of tidal generation worldwide.

"Water is nearly 800 times denser than air so it carries far more energy, making water turbines a very attractive alternative to wind energy. Notably seabed systems are not an impediment to shipping, nor do they have any visual impact and ecological issues are minimal for low-speed systems."

"When, over the test period, people stand on Richmond Bridge and watch a modest array of lights bobbing about on a buoy, they may not know it but they will be seeing the future!"

Follow the link for more information about the TorqSense torque transducer or use the form on this page.