A NEW METHOD OF CURRENT-BASED CONDITION MONITORING IN INDUCTION MACHINES OPERATING UNDER ARBITRARY LOAD CONDITIONS

Fault conditions in induction machines such as eccentric air gaps and broken rotor bars result ire harmonics in the stator current of the mo tor which can be used to monitor the health of the machine. However, v ariations in the load torque at multiples of rotational speed typicall y have the same effect on the motor current spectrum. When monitoring a single phase of the stator current, this load effect can prevent the detection of a fault condition by producing current components that o bscure those harmonics related to the condition of the machine. This p aper presents a new method for removing the load effects from the moni tored quantity of the machine. This is accomplished by comparing the a ctual stator current to a model reference value which includes the loa d effect. Simulation results illustrating the effects on the spectrum of the monitored quantity are given for both constant and eccentric ai r gaps when in the presence of an oscillating load.