A fault detection system of extracting fault signature of a motor operating at varying speed or varying load conditions is provided. The fault detection system includes a sensor interface configured to acquire sensor signals from sensors arranged at predetermined positions of the induction machine, wherein the sensor signals are indicative of an eccentricity level of a rotor of the induction machine, a memory coupled with a processor. The instructions include steps a sensor interface configured to acquire operation signals of the induction machine; a memory configured to store a computer-implemented fault detection method by extracting fault signals in the frequency domain from the frequency spectrum formed by a minimum variance beam-forming method.