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Design, construction and testing of a simple blade pitch measurement system for small wind turbines

Whale, J. (2007) Design, construction and testing of a simple blade pitch measurement system for small wind turbines. In: Renewable energy for sustainable development in the Asia Pacific region, 4-8 February, Fremantle, Western Australia

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Reliability in performance is a key factor in ensuring the sustainable operation of a small wind turbine. Despite the great potential of small wind turbines to provide electric power, particularly in remote areas, many small wind turbines have short lifetimes due to technical failures or the excessive costs of numerous maintenance visits. In developing countries where the support infrastructure for wind turbine operation and maintenance has yet to be established, turbine reliability has a higher priority than efficiency of the turbine or, to quote from Schläpfer, “10% efficiency of something is always better than 80% efficiency of nothing”.

For wind turbines to be reliable they must have in place good mechanisms to protect themselves against very high winds or sudden removal of load. Both these scenarios can lead to “over-speeding” of the turbine rotor where the rotor experiences speed excursions that exceed the rated speed of the blade manufacturer. Over-speeding can lead to blade collapse with the possibility of damage to other turbine components and people and structures in the vicinity. For small horizontal-axis wind turbines (typically in the size range 0.1 – 30 kW), passive or mechanical protection systems are often used. One common protection method is that of blade feathering where the turbine reacts to very high rotor speeds by reducing the pitch of its blades, thus regulating rotor speed by reducing the aerodynamic torque on the rotor.

Turbine reliability not only relies on using protection methods like blade feathering but it is vital that the blade pitching mechanism is tested before the turbine is installed in the field. The Research Institute of Sustainable Energy (RISE) has an Outdoor Test Area specifically designed for the field testing of renewable energy technologies. Researchers at the Outdoor Test Area have 10 years of experience in testing small wind turbines and have played a key role in the demonstration of small wind turbine technology in remote areas such as Exmouth in Western Australia and the Cocos Islands.

Measuring the degree of blade pitching produced by a blade pitching mechanism on a small wind turbine involves a number of challenges including the fact that all or part of the measurement equipment would need to be located on the rotating hub or rotor of the wind turbine. Mahmmud, Dutton and Infield report on an optical slip-ring telemetry system designed to transfer pitching moment and teeter data from the rotary frame of reference of a 16kW turbine. In general, however, manufacturers of small wind turbines cannot afford this level of detailed turbine instrumentation and rigorous testing.

The aim of this work was to develop a simple blade pitch measurement system (BPMS) that could be used to measure the changes in blade pitch produced on a small wind turbine by a blade pitching protection mechanism. The specific objectives of the work were to build a BPMS that was inexpensive and uncomplicated in design that would provide enough resolution to give a small wind turbine manufacturer clear feedback about the performance of the turbine’s blade pitching mechanism. The methodology was to design, construct and bench test the BPMS and then install the system on a small wind turbine at the RISE Outdoor Test Area in order to conduct some field testing.

Publication Type: Conference Paper
Murdoch Affiliation: School of Engineering and Energy
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