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Tracing the defects
As we mentioned in the previous article, we will continue the presentation of other concrete cases of vibrodiagnosys where defects of the electrical engines were noticed - unalignment, cam gear, loosening of the connections at the electrical installation, etc - cases validated after the repairment.

In the vibration spectrum, the unalignment is expressed through the increase of the second and the third harmonics in regard to the amplitude of the fundamental 1X. The higher the harmonics are, the more severe the unalignment is. In the image from Fig. 1 it is represented the spectrum before the alignment and after the alignment (Fig. 2).

Although the unalignment is not just an electrical defect, the functioning in these conditions determins additional filling on the bearings (specially on the semicouple bearing), followed by their accelerated wearings and the emergence in the spectrum of specific frequences of the electrical defect (variable electrical gap, etc). Depending on speed of the electric motors, deviations from the nominal accepted position vary within 0.03 ... 0.07 mm - for deviations from parallelism - and 0.04 ... 0.06 mm for the angular deviations. Recommended tolerances for alignment may be obtained using appropriate equipment. From experience, we can say that good results can be obtained using laser alignment equipment. Alignment results can be stored and reports can be issued, an example being rendered in Fig. 3.

Electric motor rotor eccentricity is manifested by the appearance of large amplitude at twice the power line frequency, in 100 Hz, and multiple harmonics, dominant frequencies in the spectrum. Rotor eccentricity occur even at new engines due to improper mounting - engine casing deformation in fixing the engine on hard (the phenomenon of "soft foot"). Vibration measurements made, if the rotor is eccentric, highlight the fundamental frequency spectrum (corresponding to the work revolution) and its harmonics are small compared with those caused by the frequency electric power grid. In the images in Fig. 4, the spectrum is presented prior to surgery and after surgery - removal of soft foot (Fig. 5).

Loose connections in the electrical installations have the effect of heating the contacts. The fastest determining of this type of fault is done by the thermographic camera. Thermographic camera produces an image on its display, the image that can be seen easily contacts unfit. Such an example is present in Fig. 6.

Thr thermographic camera can be used to investigate technological processes from the facilities, and proper functioning of dynamic equipments rolling bearings.

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Tracing the defects
As we mentioned in the previous article, we will continue the presentation of other concrete cases o
  • Read...  
The description of the solution of defections identification through the vibration analysis
For the collection of vibration spectra it was used a collector-analyser produced by SKF, type MICRO
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Vibrodiagnosis 2
As we mentioned in the previous article, the parameters of the vibrations that are collected from th
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