Motor analysis and thermal protection

A motor starting study can be completed in a matter of minutes using a PC program written for the purpose. The study uses readily available nameplate, load, and thermal-limit data and determines the most significant motor protection criterion: rotor temperature rise plotted per unit of thermal limit. The parameters for the electrical, mechanical, and thermal models are determined from the source data and used by the program to produce plots of current, torque, speed, and rotor temperature versus time. The author identifies the necessary source data and explains the method of analysis using a 6000 hp, high-inertia draft fan motor as an example