Electric motors faults, analysis and predictive maintenance 1.

Hello and welcome to this video about the 
failure and analysis of asynchronous motors. Asynchronous motors are the most common type of 
motors used. They are known for their advantages   such as low purchase price, high efficiency, easy 
regulation and simple but robust construction.  Despite their high reliability, asynchronous 
motors suffer from some malfunctions of   machine parts. We can divide failures in 
an asynchronous motor into failures of   mechanical and electrical origin, as well 
as stator, rotor and bearing failures.  Let´s start with the bearings.
All parts of the bearing are subject to   degradation. The cause of bearing failures can be 
considered as mechanical stress during rotational   movement and bearing currents. Mechanical 
stress can be caused by poor installation,   poor assembling, or by improper use, 
overloading, and poor maintenance.   The bearing currents can 
be caused by shaft voltages   (due to asymmetric electrical circuits or 
power supplies) and capacitive currents   (caused by the pulse frequency from the power 
supply control of semiconductor converters).  All mechanical (and some electrical) 
motor faults have a unique signature   in the vibration spectrum of the machine 
and vibration analysis can recognize them.   Failures such as misalignment, looseness, 
unbalance and bearing faults are diagnosed   according to the same rules applicable 
for all other machinery parts.   How do we analyze mechanical faults? Get the 
answer for example from our video named How   to become an expert in Vibration Analysis and our 
other tutorial videos.

What is vibration analysis?   Our series of Vibration analysis for beginners 
videos will help you to understand this topic.  Some electrical faults are recognizable 
in the vibration spectrum too.   You should measure the motor with and 
without a power supply in order to find them.   Some vibration signatures could disappear after 
power off – those with an electrical origin.   You can also focus on the exact 
frequency of peaks in the spectrum.   If you find a peak with your exact current 
supply frequency (for example 50Hz and more   often on its harmonic frequencies) it is probably 
an electric issue because there is always some   slip on a loaded electric motor and the motor 
isn´t running on its exact rotation frequency.  Electrical (and some mechanical) 
motor faults have a unique signature   in the frequency spectrum of the motor 
current. The MCSA method can recognize them.   MCSA stands for: Motor Current Signature Analysis.  Excessive sidebands are created in electric 
motors, which distort the frequency spectrum.   Each fault then has its specific signature. 
Individual defects can be distinguished   from each other according to the amplitude 
bands and the frequency or other signatures.  The basis of this method is to measure the 
course of the stator current of one or more   phases in the time domain and 
its subsequent spectral analysis.

pexels photo 11039667

Stator faults
Stator winding faults cause the   majority problems in stators. Broken winding 
insulation is the most common stator fault.   MCSA can recognize broken 
insulation between threads,   which can lead to broken insulation between 
phases and it is fatal for the motor.   Thermal stress has the greatest impact 
on the life and quality of insulation.   Another undesirable effect is the 
electrical stress of the transient voltage.   In the case of more and more frequent 
use of inverters for soft-start,   rectangular voltage pulses are 
modulated at the output of the inverter.  Rotor faults
The rotor of an asynchronous motor   consists of a shaft, insulated sheets pressed on 
the shaft which form the rotor magnetic circuit   and windings. Mostly the winding of 
the rotor consists of a cage structure,   which is formed by bars, which 
are connected at the ends.  Rotor eccentricity (meaning the unevenness of 
the air gap between the rotor and the stator)   and rotor bar interruption 
are the most common faults.   The cause of these faults can be 
the use of poor-quality materials,   overloading or heavy starts.   In the case of rotor bars, the fault may increase 
the resistance of the bar, or completely break   the bar electrical circuit.

Rotor bar failures 
result mainly in engine starting deterioration   and generating parasitic moments. Also, the broken 
bar causes additional faults in other bars because   the current in them is greater due to the missing 
bar current path (where one bar is broken).  The ADASH VA5Pro vibration analyzer offers 
the unique capability of analyzing vibration   and current in one device. In addition, the MCSA 
module expands the capabilities of the analyzer   and allows you to do analysis of the current 
signature from the spectrum – based on your   knowledge and experience, or you can use the 
automatic detection function. It is a similar   feature to the ADASH automatic Fault Source 
Identification Tool (FASIT) for vibration   analysis. The device can automatically recognize 
the main causes of failures such as unbalance,   looseness, misalignment and bearing faults. 
The MCSA module of the VA5Pro device is able   to automatically identify rotor and stator faults, 
eccentricity, broken rotor bars and power quality.

As found on YouTube

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