Sparking, electrical discharge, and heating in synchronous and induction machines: can it be controlled?

It is impossible to eliminate all occurrences of sparking and localized heating from the interior of electric machines during the 20-40 years that they are normally in service. One can minimize the probability of sparking and localized heating by exercising precautions which will eliminate or minimize the sources of these conditions in AC machines. Most new machines have a low probability of sparking, but some design steps can be taken which condition the machine as a sparking type or a nonsparking type. This paper discusses the aspects of arcing between rotor and stator in the air gap, sparking between rotor parts, sparking between frame components, sparking due to broken or open bars and endrings, and surface discharge on the stator winding. Also discussed is what action, if any, can be taken in design, application, and maintenance to eliminate or control these problems.