Effect of cyclic loading on motor efficiency

A method of sizing motors is proposed which is intended to provide the least energy consumption and more starting torque. The technique compares steady-load motor efficiency with the efficiency when operated on various cyclic load configurations. The performance of unconventional and conventional pumping units is compared for calculated and measured torques. Field data are used to verify the model. For cyclic loads, motors are more efficient when operated near half-load. The reason for improved efficiency when using unconventional units is shown. It is shown that the best efficiency will be achieved with a motor operating at 40-50% of its rating. A ten-point improvement in efficiency is obtained when the motor load changes by a factor of 2 and the final load is near 50%. A motor provides adequate starting torque for a conventional unit only when the motor rating is two times the average load.<>