Invasive Methods to Diagnose Stator Winding and Bearing Defects of an Induction Motors

Invasive Methods to Diagnose Stator Winding and Bearing Defects of an Induction Motors

Muhammad Aman Sheikh, Nordin B. Saad, Nursyarizal Mohd Nor, Sheikh Tahir Bakhsh, Muhammad Irfan
DOI: 10.4018/978-1-5225-6989-3.ch006
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Condition monitoring in an induction motor must concentrate on the root causes of the failure modes that exhibit a slow failure sequence. According to published surveys, two-fifths of the faults are due to bearing failures. Inter-turn short circuit faults in stator windings are approximately responsible for one-third of the motor faults. In the last few decades, various methods and alternative techniques have been proposed and implemented to diagnose induction motor faults. In an induction motor, stator winding and bearing faults account the largest percentage of motor failure. Due to the fact these faults can lead the motor to catastrophic failure that are expensive in term of maintenance cost, wastage raw material, and unplanned shutdown. Thus, to diagnose the state of motor and overcome existing problem, the chapter provides detailed invasive methods which are proposed and are currently in practice. Moreover, the chapter also highlights the limitation, scope, and the challenges of existing invasive condition monitoring techniques.
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Invasive Fault Diagnosis Methods

The faults have various effects on physical, electrical, and magnetic properties of the induction motor. Thus, the variation in the properties or behaviour of the motor help to extract the fault index. The fault can be properly identified by detecting and measuring the effects on the properties of the motor. Mostly in invasive fault diagnosis methods, the fault index detection and measurement require special sensors to be installed on the frame of the induction motor. Next subsection introduces the approaches adopted in invasive method to identify the fault.

Acoustic Noise

Acoustic noise is a transient flexible signal that is generated due to permanent deformation of an equipment and these signals can propagate through solid materials. The frequencies associated with acoustic noise are beyond the audible range 20 KHz. Winding and bearing faults can be identified by acoustic noise (Kharche & Kshirsagar, 2014; Germen, Basaran & Fidan, 2014; Mirafzal, Povinelli & Demerdash, 2006). Acoustic noise spectrum of induction motor includes electromagnetic motive (EM) and air conditioning noise. The air conditioning noise relates the distortion of periodic air pressure affected by the rotational parts. While the EM noise refers Maxwell stress on the metal surfaces in the presence of a magnetic field. These stresses in the presences of a magnetic field, induce vibration in the structure of the induction motor that in result emits noise radiation. The mechanical noise and aerodynamic noise are in the range of 12 dB per ester of the speed of induction motor. The higher the speed of induction motor the higher will be EM noise. A limitation of this technique is the requirement of special sensor and acquisition system that should capture acoustic signals with sufficient resolution because the sampling rate is very high typically 2 MHz. This subsequent constraint the diagnosis system to employ more advanced and expensive acquisition systems. Therefore, for long term installations of the senor with limited lifetime in order to manage large volumes of data with extremely fast data rate should be proposed to deal such a huge data rates. Moreover, this technique does not highlight the segregation issue of the stator winding and bearing raceways defects.

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