EVALUATION AND IMPLEMENTATION OF A SYSTEM TO ELIMINATE ARBITRARY LOADEFFECTS IN CURRENT-BASED MONITORING OF INDUCTION MACHINES

This paper presents a method for removing the load effects from the mo nitored quantity of the machine, Fault conditions in induction machine s cause the magnetic field in the airgap of the machine to be nonunifo rm. This results in harmonics in the stator current of the motor which can be measured in order to determine the health of the motor, Howeve r, variations in the load torque which are not related to the health o f the machine typically have exactly the same effect on the load curre nt. Previously presented schemes for current-based condition monitorin g ignore the load effect or assume it is known, Therefore, a scheme fo r determining machine health in the presence of a varying load torque requires some method for separating the two effects, This is accomplis hed by comparing the actual stator current to a model reference value which includes the load effects, The difference between these two sign als provides a filtered quantity, independent of variations of the loa d, that allows continuous on-line condition monitoring to be conducted without concern for the load condition, Simulation and test results i llustrate the effects on the spectrum of the monitored quantity for bo th constant and eccentric airgaps when in the presence of an oscillati ng load.