Torque sensor helps ensure reliability of tidal turbine

Non-contact torque sensors from Sensor Technology are playing a key role in the development of commercial-scale in-stream tidal turbines produced by OpenHydro. This Irish company is using TorqSense torque sensors, which are based on surface acoustic wave (SAW) technology, to accurately measure rotational speed and frictional forces in a simulator for the turbine bearings, thereby enabling it to optimise the performance and reliability of its innovative products.

OpenHydro designs and manufactures marine turbines to generate renewable energy from tidal streams. The company's vision is to deploy farms of tidal turbines under the world's oceans, where they will dependably generate electricity with no cost to the environment. This method of producing electricity has many benefits.

Reliably and efficiently harvesting energy from the tides, however, requires the use of novel technology and, in the case of OpenHydro, this takes the form of open-centre turbines that can be deployed directly on the seabed. Clearly, installation in such an inaccessible location makes reliability a prime consideration in the design and construction of the turbines. For this reason, OpenHydro carefully and comprehensively evaluates the performance of all of the components used in its turbines.

Simulator

For the bearings, this evaluation involves the use of a simulator that enables the company's engineers to determine how frictional forces in the bearings vary with different loads and rotational speeds. Central to the operation of this simulator is the measurement of torque in a shaft from the motor that drives the bearing under test. With conventional sensors, it is difficult to carry out this type of torque measurement accurately and reliably, but OpenHydro found that Sensor Technology's TorqSense RWT320 series sensor was suitable.

Kevin Harnett, a Mechanical Engineer at OpenHydro, comments: "We chose the RWT320 because of its convenient wireless operation, and because it was easy for us to fix in line with an existing shaft in our experimental set up. In addition, this model of sensor has integral electronics and a serial output, which means that we can link it directly to a laptop computer in our test laboratory. This is a very straightforward and convenient arrangement."

OpenHydro uses the RWT320 sensor in conjunction with Sensor Technology's TorqView software. This offers a choice of dial, digital bar and chart graph format display for torque, RPM, temperature and power. It also provides facilities for real-time plotting and for data recording, and can output stored results as files that are compatible with Matlab and Excel.

Harnett states: "We have found both the sensor and the software very easy to work with, and the sensor has proved itself to be well able to withstand the tough operating conditions in our laboratory. We have also received excellent technical support from Sensor Technology, which was very helpful as we have never previously worked with sensors of this type. Overall, we are very happy with product and the service we have received, and the sensor is providing invaluable data for our development work."

Proof that this development work is yielding dividends was amply provided late in 2009, when OpenHydro deployed the first commercial-scale in-stream tidal turbine in the Bay of Fundy, Canada, on behalf of its customer, Nova Scotia Power. This 1MW unit arrived on site on 11 November and was operational, rotating with the tides, collecting data and producing energy by 17 November.

Follow the link for more information about the TorqSense RWT320 series torque sensor or use the form on this page.