Application of Piezoelectric Sensors to Rotor Fault Diagnostics in Squirrel-Cage Induction Machines

In this paper, application of a piezoelectric vibration sensor to induction motor fault diagnostics is investigated. More specifically, a piezoelectric sensor is used to diagnose broken bar faults in squirrel-cage induction machines. The piezoelectric vibration sensor described in this paper offers a number of advantages when compared to other conventional vibration monitoring devices, such as accelerometers, velomitors, proximity probes, etc. These advantages can be summarized as follows: low cost, ease of implementation, and relatively high bandwidth. Use of a vibration signal as a medium for rotor fault diagnostics may result in a simplification of the diagnosis procedure, since both the fault index and the slip (speed) can be estimated from one signal. It is well known that rotor faults result in torque and possible consequent speed oscillations at twice the slip frequency, 2sf. These torque and speed oscillations/pulsations, in turn, produce detectable vibrations that can be utilized for purposes of rotor fault diagnostics. Moreover, radial forces produced as a result of such faults may result in increased vibration amplitude at the same, 2sf, frequency, which can further amplify the fault index, and hence make the proposed technique more reliable. Experimental results on broken bar diagnostics are presented here to demonstrate the validity and efficacy of this approach.