Evaluating the Effects of Motor Starting on Industrial and Commercial Power Systems

The motors being applied on modern industrial systems are becoming increasingly large in size. Starting these large motors, especially across-the-line, will produce a transient voltage depression that can substantially reduce the motor output torque while severely influencing the operation of any locally connected load, as well as loads served by buses electrically remote from the point of motor starting. Motors with special starting characteristics and reduced voltage starting equipment may reduce motor inrush and the associated voltage dip, but the starting performance of the motor may be unacceptably altered. How computer aided studies are of benefit in exploring the problems associated with starting large motors on industrial systems is discussed. Several types of studies that are presently available are described, and the data or information required to perform these studies are reviewed. Finally the results that can be expected from a motor starting study effort are examined.