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A wind power coupling with integrated safety brake

06 October 2010

While conventional hydraulic brakes apply the greatest braking force on a wind turbine shaft, they are inherently unreliable. Electromagnetic brakes, on the other hand, have proved themselves over many years in the safety-critical elevator industry and could offer a more reliable alternative

Wind power turbines place high demands on the connection between gearbox and generator. Substantial shock torque, together with high shaft misalignments, must be adequately catered for during the running life of the installation, which can be anything up to 20 years. It is therefore important to develop a low maintenance solution to this problem that not only offers overload protection but also electrical isolation to prevent leakage currents from damaging the driveline.

Instead of simply offering a specified brake disk integrated with a coupling, Mayr Power Transmissions has taken the logical step of offering a complete modular system, drawing on its applications knowledge of torque limiters, shaft couplings and electromagnetic safety brakes.

Although conventional hydraulic brakes can apply high braking forces, they are more prone to failure due to leaking callipers, damaged hoses and valve wear, resulting in downtime and high maintenance and repair costs. Mayr’s ROBA-diskstop electromagnetic brake, which has proven its worth in the safety critical elevator industry over many years, is a viable alternative for small and medium sized wind power installations.

Under normal conditions, the turbine rotor is slowed by feathering the pitch of the blades, thus reducing the rotor speed before engaging the brakes. On emergency stop, the brakes have to engage at full generator speed and are subject to very high frictional forces. To cope with this, Mayr has developed special sintered brake linings that offer high thermal stability, more reliable surface pressures and very low wear rates.

At the core of the module is its ROBA-DS coupling, featuring an electrically isolating glass-reinforced plastic intermediate sleeve, which can be disassembled without having to move the gearbox or generator. The coupling can accommodate up to four degrees of misalignment and, using the latest computer modelling tools, its torsional and compensation rigidity values can be optimised according to customer requirements at the design stage.

Overload protection is achieved by an integrated frictionally locked sleeve fabricated from a special friction material that maintains a stable and repeatable release torque that varies by no more than +/-15% in 1,000 release cycles. For security, the overload module is calibrated during manufacture to prevent the possibility of adjustment errors during installation.

The whole wind power module is maintenance free over its entire service lifetime when used under normal turbine operating conditions. Where abnormal friction work is encountered, all that is required is periodic inspection and renewal of the brake linings.

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