Wind power coupling with integrated safety brake
With extensive experience in provide bespoke solutions for both horizontal and vertical axis wind turbines, Mayr Power Transmissions has taken a new look at overload protection, with a new modular coupling and braking system.
Wind power plants place high demands on the connection between gearbox and generator. Substantial shock torques together with high shaft misalignments must be adequately catered for during the running life of up to 20 years. The profitability of wind power plants, particularly in offshore installations, is dependent both on the wind conditions and on operational reliability and the impact of any downtime.
Downtime can be minimised through appropriate drive components. As an example, it is important to develop low maintenance solutions that offer protection against unpermitted overloads and electrical isolation to prevent leakage currents damaging the driveline.
Instead of simply offering a customer specified brake disk integrated to a coupling, Mayr Power Transmissions has taken the logical step of offering a complete modular system, drawing on its decades of experience with torque limiters, shaft couplings and electromagnetic safety brakes. Although conventional hydraulic brakes can apply high brake torque, they are more prone to failure due to leaking callipers, damaged hoses and wear on the valves resulting in downtime and high maintenance and repair costs. Mayr's alternative is the ROBA-diskstop electromagnetic brake, which has proven its worth in the safety critical elevator industry over many years. A viable alternative for small and medium wind power installations, the Mayr ROBA-diskstop combines high reliability with high braking torques in a cost-effective patented design.
Under normal conditions, the turbine rotor is slowed by feathering the pitch of the blades, reducing the rotor speed before engaging the brakes. On emergency stop, the brakes have to engage at full generator speed and absorb very high frictional work. To cope with this, Mayr has developed special sintered brake linings which offer high thermal stability, more reliable surface pressures and very low wear rates.
At the core of the module is the patented ROBA-DS coupling featuring an electrically isolating GRP intermediate sleeve which can be disassembled without moving the gearbox or generator radially. The high performance density means the coupling can deliver high torque from a highly compact design.
Wear free and maintenance-free, the coupling can accommodate up to 4° of misalignment and, using the latest computer modelling tools, the coupling's torsional and compensation rigidity values can be optimised in line with customer and operational requirements at the design stage. Overload protection is achieved by an integrated frictionally locked sleeve. The special friction material has been designed to maintain a stable and repeatable release torque exhibiting a tolerance of ±15% over 1000 releases. For security, the overload module is calibrated during manufacture to prevent the possibility of adjustment errors during installation.
The disk packs and the intermediate sleeve can be radially installed and removed without axial displacement of the hubs being required. The use of special clamping nuts makes it possible to install the disk packs with low tightening torques. The whole wind power module is designed to be maintenance-free over its entire service lifetime when used under normal turbine operating conditions. Where high friction work is encountered all that is required is periodic inspection and renewal of the brake linings.
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