Mitigation of Torsional Oscillations Hazard in Cascaded Induction Motors Driving a Large Mechanical Load

This paper presents a mitigation method for the torsional oscillations and stresses occurring in a cascaded set of 2 induction motors driving large mechanical load through elastic mechanical shafts. The idea of using cascaded induction motors connected through mechanical shaft sections can be used to drive a large mechanical load. The usage of such electromechanical system is popular in industrial applications like mining, oil and gas industry. However, a little scope of work was introduced to present a mitigation method for torsional stresses that may be appeared on the mechanical shaft sections while the system starts against full load condition. The analysis of transient performance for such electromechanical system is essential to ensure the operational reliability of the system parts. An effective starting technique by using variable frequency drives is introduced to mitigate the destructive effects of high torsional oscillations that has a bad effect on the mechanical shaft sections. The electromechanical system was implemented using Matlab/Simulink. The electrical & mechanical system mathematical models were developed in ABC reference frame. Results indicate that torsional stresses are minimized and suppressed while using variable frequency drives to start the induction motors instead of direct online starting.

I. Introduction

Three phase induction motors are considered the most common used motors in industrial applications. Due to their simplicity, reduced maintenance, high performance & cheap price, they are considered the most widespread electrical machine for industrial applications. Different industrial applications requires the usage of induction motors to drive mechanical and inertia loads such as compressors, pumps, fans, conveyors, crushers & mills.