Using preloading to protect bearings against lightning damage

Abstract

When a radar system onboard a ship is struck by lightning the current has to be conducted via defined paths to prevent damage. A key element to protect is the bearing system between the rotating and stationary part. The conventional way of protecting bearing is to provide a bypass current path via additional measures such as a slip ring. The main cause of damage to the bearing system is the arcing due to high voltage difference between rollers and raceway. It is commonly assumed that, if the radar is rotating, the lubrication between the rolling elements and the raceway is a non-electrical conducting hydrodynamic lubrication layer, and high voltages can be developed. But if the bearing is sufficiently preloaded it is still providing a conductive path via boundary lubrication. No arcing occurs, and no damage. The concept of pre-loading the bearing system has been evaluated using many experiments on stationary and rotating bearings, and after performing endurance testing.