97-10: Mechanical Damage Caused by EMF Generated from Fast Bus Reclosure

Energy conservation considerations have led to the increasing use of two speed motors and variable frequency drives for mechanical draft cooling towers. While this practice has resulted in improved efficiency, its proper application has several hidden pitfalls that must be considered when specifying the motor control and mechanical components in the system. The potential damage tooth electric motors and the connected equipment that is caused by fast switching or fast bus reclosure can be quite extensive. This paper discusses the details of motor reaction to fast switching, illustrates damage caused to mechanical components and recommends prevention.