Wind energy has grown to be the major source of renewable energy and safe operation of wind turbines is increasingly important. It is essential for wind turbines to stop operating in the case of failure of critical components and, importantly, at wind speeds over a critical limit. Failure to brake the wind turbine rotation may result in catastrophic damage, jeopardising investments, reputation and reliability of wind energy assets. Wind turbine brake systems are generally monitored by the operator's manual incpections and observations. Automated online performance and condition monitoring of braking systems leads to early fault detection of the system components and also helps to minimise the number of major breakdowns, reducing downtimes. In this paper the braking mechanisms of a stall- and a pitch-regulated wind turbine are discussed. The present study explores an online condition monitoring approach of the braking system hydraulic power currents and the speed of the high speed shaft as a comprehensive method of brake system fault diagnosis. Measurements of the high speed shaft and electrical currents in the hydraulic unit can be effectively used to monitor the condition of the brakes and lead to successful detection of faults.
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