Drop in Motors, What You Need to Consider Beyond the Bolt Pattern

The push to improve efficiency and lower cost has impacted electric motors. It is not uncommon to see a reduction in mass for modern medium voltage machines, and the actual footprint of the newer machines is smaller in most cases as well. Many drop in motors (mechanically interchangeable) perform very well. There are design constraints that may be overlooked when ordering a functional drop in replacement machine. Depending on the power, size, and speed of the motor, failure to meet the minimum base stiffness requirements can cause severe vibration issues. The combination of a transition base with a machine of a different mass can cause resonance issues, which can cost more than the motor to resolve. Changing from a stiff to a flexible rotor can cause unexpected vibration issues without an easy solution. The case study issues described in this paper could be experienced by any end user regardless of the original equipment manufacturer.