A Mathematical Model to Simulate Vertical Motors and Calculate Reed Critical Frequency

This paper provides a mathematical model for calculating the reed critical frequency (RCF) of vertical motors on a massive rigid base. Typical methods of predicting RCF of vertical motors are performing a bump test on the motor or performing a full model simulation using Finite Element Analysis (FEA) or following the method given by NEMA where a motor could be considered as a single degree of freedom spring-mass system and static deflection at its center of gravity. However, these methods can sometimes prove to be expensive as well as time consuming. Another challenge is to predict RCF accurately so as to avoid any chance of harmonic interaction with driven equipment. This makes it crucial for motor manufacturers to submit motor outlines with RCF within +/-10% accuracy. The discussed model in this paper considers a vertical motor as a two degree of freedom spring-mass system and calculates RCF after simplifying the complete motor into equivalent structures using beam theory. This mathematical model is developed for calculating static deflection, the center of gravity and RCF for vertical motors where a user could select different enclosures, configurations and predict RCF. This model not only optimizes resources but provides accurate RCF.