Non-Invasive Technologies for Condition Monitoring of Synchronous Motors

Abstract: The modern industry today is highly dependent on electric motors of differenttypes and sizes. Synchronous motors are used in applications where a fixedspeed is desired. These machines are often found in high power applicationswhere they are preferred over induction motors due to their higher efficiency.Synchronous motors represent large investments and typically drive processeswhere downtime results in significant capital losses. Thus, detecting faults atan early stage can help avoid catastrophic failures and be useful in thescheduling of maintenance. In order to detect faulty conditions before theyterminate in a failure, machine operators must perform some kind ofmonitoring on the machines. Typically, the more critical the machine is for aprocess, the more effort is put on monitoring it. Before building a monitoringsystem for a machine, one must first decide what parameters that should bemonitored. The obvious desire is to find a parameter that is easy and cheap tomeasure and at the same time can give detailed information about the workingstate of the machine.The aim of this thesis is to evaluate whether the exciter stator current is anadequate parameter to use within a monitoring system for synchronous motors.The evaluation has been made through simulations of two different setups;One using a synchronous motor in the 20 MW range fed by a synchronousmachine type exciter. And the other using the same motor but instead fed byan induction machine type exciter. It has been found that the exciter statorcurrent can be used for detection of faults associated to the rectifier and statorshort circuit of the main machine stator winding. It has not been possible todetect turn-to-turn faults in the main machine rotor.The work has been performed at ABB Corporate Research in Västerås fromJune until December 2013.