ABSTRACT
Oil is used on circuit breakers and transformers as an insulation to smooth the stress that results from electric voltage. In the case of rotating machines such as motors and generators, there is no oil insulation and the windings are equipped with dry insulation. Therefore, rotating machines are more vulnerable to high stress and failure compared to circuit breakers or transformers. With the fast front transients, the winding structure can cause surge reflections and oscillations that can damage winding insulation. There are rotating machines connected directly to overhead lines and exposed to lightning surges. Other electrical machines are connected through transformers and are exposed to traveling waves produced by lightning strikes. There are overvoltages generated due to insulation failure of the electric motor. Such effects are important in the reliable operation of the motor. Almost all rotating machines are exposed to lightning surges, switching surges, and internally generated surge voltages [1-5].
