March 2012
Reliable holding brakes for wind turbines
Braking in extreme conditions
Brakes manufactured by INTORQ are in use for wind turbine installations across Europe and worldwide. There are two particular applications where normally-on spring applied holding brakes are needed. Firstly on the blade pitch drives where servo motors continually adjust the blade angle to maintain the running speed - here the brakes hold the blades in a fixed position during periods of shutdown. Secondly brakes are needed on the azimuth drives which rotate the nacelle into wind. Here the brakes hold the position except when adjustment is needed. In both cases brakes must withstand extremes & temperature and damp conditions with minimal maintenance.
INTORQ BFK series brakes are used by several wind turbine manufacturers with torques from 14 to 200Nm. These brakes are often customised but are always single disc design with multiple engagement springs and DC coil release. They are mounted onto the back of the motors; servo motors for the pitch drives and standard asynchronous motors for the azimuth drives of which there are typically 4 or 5 on a wind turbine. They are designed for 100% running time with coil engaged and the rated torque can be applied with either dynamic or static brake engagement.
Brake modifications to suit the environment start with what is known as the ‘Cold Climate Version’ allowing operation with ambients from -20∘C to +40∘C. Corrosion resistant friction surfaces are used together with zinc plated housings. Low backlash is important to prevent oscillations from wind loadings. Here INTORQ provide a plastic coating to the splines of the brake disc which reduces backlash to almost zero and extends the service life. To ensure reliable brake release, even with large air gaps, a specially developed brake rectifier is used which gives a temporary over-excitation of the brake coil. This also helps reduce the brake engagement time.
Wind turbines present some of the most challenging conditions for industrial brakes, and the need for reliability and low maintenance is evident. INTORQ brakes are developed to meet these challenges as can be seen from B10d lifetime ratings of up to 20 million hours. The full INTORQ range covering spring applied brakes from 0.1 to 2400Nm is available in the UK through Techdrives, www.techdrives.co.uk
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