Starting high inertia loads on adjustable speed drives

Abstract

When starting motors with high inertia loads across the line, it is common practice to determine load inertia and then make acceleration time calculations. Comparing acceleration time to the motor's maximum allowable time to accelerate, the motor can be used or, if necessary, the next larger rating may be required because the acceleration time with a particular inertia is too long. It is not uncommon to find a motor to be sized for the starting/accelerating load instead of the running load in applications with high inertia loads. What should be done differently when an adjustable speed drive (ASD) is applied on these loads with high inertia? In this article, a method is established to calculate running torque, calculate starting/accelerating torque, and size the motor and the ASD appropriately.