Experimental technique for estimation of mechanical load unbalance level: Based on time analysis of induction machine stator current

Traditional fault diagnostic techniques using motor current signature analysis is, generally, based on the assumption of a constant load torque. In fact, due to the design, construction, and ageing phenomenon of loads, torque imposed to the motor can not be strictly constant and, in most of cases, varies according to the machine rotor position. These variations of the load torque, which are not related to the health of the motor, involve amplitude modulation of machine stator current at rotational frequency. In this paper we propose a technique based on the introduction of a supplementary known mechanical unbalance on the motor rotor axis to estimate the unknown load unbalance level from time analysis of stator current signal. Simulation and experimental results show the effectiveness of the proposed method.