Lightning protection analysis of main shaft bearings in wind turbine generators

One of the major reasons for downtime of wind turbine generators is damage due to lightning strikes. As a result, main shaft bearings at the interface between the rotor and the nacelle have to be protected with a proper lightning protection system. This paper uses wind turbine simulations in PSCAD to evaluate various protection techniques for the main shaft bearings. Lightning protection of bearings by the use of spark gaps, sliding contacts, and a combination of both are quantitatively analyzed here. Finally, an efficient solution for protecting the bearings is recommended. This involves the parallel connection of spark gaps and sliding contacts by which lightning current conduction can be almost completely bypassed from the bearings. Sliding contacts carry the current until the ignition of spark gaps takes place and then current will be shared by the spark gaps to reduce the stress and damage to the sliding contacts.