Motor Design Slip Performance on Cyclic Loads

Cyclic loads such as eccentric pumping units cause a varying torque on the driver. Determination of the most efficient induction motor for the load is discussed. Ultrahigh-slip motors as well as NEMA (National Electric Manufacturers Association) design motors are evaluated. Comparisons of operating costs and investments are presented. The following is concluded: (1) any motor design will work on a pumping unit; (2) the motor must be carefully sized to provide minimum operating cost; (3) the lowest operating cost and the least investment come from the motors with the least slip; (4) the lower-slip motors cause an increase in peak torque on the unit; and (5) an accurate computer model with an easy-to-use program that allows what-if options is highly desirable.