Long-term high resolution wear studies of high current density electrical brushes

With renewed interest in sliding electrical contacts for application in doubly-fed asynchronous induction wind turbine generators, focus on optimizing the wear life of high current density electrical brushes has re-emerged. This is due to the service and maintenance costs associated with some wind turbine sites, especially offshore. An automated test apparatus has been built and tests conducted to study the long-term wear behavior of silver-graphite brushes running on tin-bronze slip rings with high time- and spatial resolution. The results of the tests have shown that the tribo-film deposited on the slip ring adapts rapidly to changing operating conditions such as current load. The tests have also indicated that the long-term brush wear behavior is surprisingly dynamic and that the wear process may be subject to tribo-film instabilities which account for short periods of rapid wear separated by longer periods of mild wear.