Preventing lightning damage in bearings by using mechanical preloading

High positioned systems such as wind turbines or radar system onboard a ship can be easily struck bylightning. The lightning current has to be conducted via defined paths to prevent damage. A key elementto protect is the bearing system between the rotating and stationary part. Providing a bypass currentpath via additional measures such as a slip ring is the conventional way of protecting bearing. The arcingdue to high voltage difference between rollers and raceway is however the main cause of damage to thebearing system. It is commonly assumed that, if the wind turbine blades, or the radar, is rotating, thelubrication between the rolling elements and the raceway is a non-electrical conducting hydrodynamiclubrication layer, and thus high voltages can be developed. But if the bearing is sufficiently preloadedit is still providing a conductive path via boundary lubrication. No arcing occurs, and no damage. Theconcept of pre-loading the bearing system has been evaluated using many experiments on stationaryand rotating bearings, and after performing endurance testing.