25-08-2017, 09:32 PM
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I. Abstract
Induction motors are widely used in industries for the conversion ofelectrical energy into mechanical energy. Fault
detection and diagnosisof asynchronous
machine has become a central problem in
industry over the past decade.The proposed
bearing method detects the faultsof three
Phase induction motor byanalysis of byanalysis of themotor. The experimental data from theinductionmotor are acquired under healthy andfaultyconditions of the motor.The experimental results show that these impacts are so strong that even simplefrequency-domain indices are able to
detect bearing defects.
I. Introduction
Bearing failures are the most common failure mode in Induction motor that may lead to motor breakdown, equipment defect, and even human casualties [1] and [2] .
Zhou et.al [3] have reviewed different bearing condition monitoring (BCM) methods for electric machines and
concluded that vibration and current monitoring are more popular in industry
and research. Vibration monitoring has some problems such as being expensive, limitation of proximity vibration sensors to machine, and sensor failure. On other hand, motor current monitoring is non-invasive, and can be implemented from motor control center remotely. It is important to mention that the possibility of false fault detection using motor current signal analysis (MCSA) is high because fault signal have small amplitudes and are buried in noise [4]. In addition, extracting the fault signal from current signal involves utilizing advanced digital signal processing(DSP) techniques and it is usually computationally expensive.
In [5], the application of MCSA is used for the detection of bearing damage in IMs. The method of has used MCSA in IM for fault diagnosis. It proposes an algorithm for motor fault detection which analyzes the spectrogram based on a Fast Fourier transform and Short – time Fourier transform. The method of proposed an approach to detect in bearing fault via motor signal.
The proposed method detects bearing faults using analysis of frequency spectrum of motor current signal. It is shown that bearing defect has impacts on the frequency of motor current signal. These effects are obviously visible in FFT and STFT of signal.
This paper is structured as follows: In section II, theoretical background including bearing faults, Impact of bearing defects on the frequency of motor current signal. The experimental setup used in this research is addressed in section III. In section IV the experimental results are presented. Finally, the conclusions are made in section V.
II. THEORETICAL BACKGOOUND
A. Bearing Faults
Typical structure of a ball bearing is show in fig.1. The main components of ball bearing are inner raceway, outer raceway, and ball elements. If a fault occurs in the bearing components, proportional to the type of the bearing components a unique frequency will be produced. The value of this fault frequency depends on the operating speed and geometry of the bearing.
B. Impact of bearing defects on the frequency of motor current signal
There are two magnetic fields in the induction motor air gap, stator winding and rotor bars. The angular speed of stator magnetic field is affected by the frequency of stator current. But the angular speed of rotor magnetic fields is affected by the rotor bar current frequency and mechanical rotor angular speed. When the rotor rotates, impulsive forces caused by defective bearing to high frequency vibration with short- time duration in the rotor bearing system. The impact of impulsive forces is immediately revealed on the rotor speed as periodic high frequency disturbances. These disturbances cannot be rapidly compensated in the rotor bar currents. Therefore, the angular velocity of the resultant air gap magnetic field contain these disturbances and induced voltage in stator windings are affected. Thus the frequency of motor current is affected by bearing defects.