Carbon brush performance on slip rings

Carbon brushes are commonly used on DC or AC applications such as commutators and slip rings. The commutator application has been studied extensively and there are many trouble shooting tools to assist the technician at resolving motor or generator problems. Slip ring applications have been widely used on high speed turbine generators, slower speed synchronous motor/generators and wound rotor motors. In recent years, with the aid of modern electronics, the doubly fed asynchronous generator and wound rotor motor have increased in popularity. Troubleshooting tools for the slip ring application used on this type of equipment are limited. This paper will address the modes of failure for carbon brushes and slip rings and the root cause analysis for these failures. The information for this paper was generated from motor/generator inspections over a large range of applications. The intent of this paper is to assist the technician with the evaluation of slip rings and carbon brushes in order to reduce maintenance cost and increase uptime.