Motor Failures due to Steep Fronted Switching Surges: The Need for Surge Protection - User's Experience

The presence of steep fronted wave surges is well documented and accepted throughout the utility and petrochemical industry. Technical literature covering this subject directs the attention of the designer and the user to the failures of many large ac motors which are caused by steep fronted switching surges such as those generated by air, vacuum, and station type circuit breakers. These surges cause severe stress on the insulation of the stator windings due to the nonuniform distribution of voltage across windings. Furthermore, it is pointed out that the absence of acceptable national standards defining the impulse voltage withstand capability of rotating machines, as applied on static equipment, has led to inconsistency, uncertainty, and failures of many large ac motors. Based on available technical literature, recent national studies, and user experience, the need to specify extra dielectric strength for turn-to-turn insulation to withstand the overvoltages and the need for acceptable national standards and testing requirements will be presented in the paper. Application of lightning arresters will not be discussed in this paper since numerous other IEEE papers have covered this subject extensively