Start-Up Simulations for Induction and Synchronous Motor Driven Compressor Trains

Abstract

3-phase motors (both induction and synchronous) have remained the workhorse of the turbomachinery industry for several decades now. It is well known that motor driven centrifugal compressors give rise to transient torques during start-up of the drive train. The torsional nature of the shaft torques necessitates a thorough analysis at the design stage in order to adequately size the mechanical components of the drive train. This paper summarizes the mathematical equations to predict the air-gap torque for induction and synchronous motors that are available readily from electrical engineering literature, and extends it to present the electro-mechanical equations of motion for the motor-compressor system. Drive train studies have been simulated for both the traditional across-the-line start voltage systems and a simplified version of the more modern soft-start (variable frequency drive) systems.