Latvian Maritime academy

The mechanical defects in the running slots of the bearing rings, rotating bodies and separators result
in slowing down of the rotor, micro changes of its angular velocity and acceleration, changing in the
space position of rotor in the stator boring. It results in different electromagnetic interaction of rotor and
stator, in the oscillations of rotating electro-magnetic torque. The harmonics (typical frequencies) the
amplitude and frequency of which depend on the technical condition of the bearing unit appear in the
spectrum of the consumed current. The frequency and amplitude of these harmonics are the diagnostic
parameters.
The operating rolling bearing generates mechanical oscillations divisible by basic frequency of
rotation of the three-phase electric motor. These frequencies are called typical.
f = k 1 *f n , (1)
where: f – are the typical frequencies;
k 1 = 1…5 – coefficients;
f n – the typical frequencies when there are defects in the bearings elements. In some cases
coefficient k 1 can get a value within the range 04…-0,8 f n .
The basic characteristics of the spectral analysis of vibro-acoustics as well as the spectral
components of the consumed currents are the frequency and amplitude. 5 typical frequencies, the
amplitudes of which are very different for the bearing unit with defect and for that being defect-free, can
be calculated for the rolling bearing [1, 13].
Figure 1. The basic parameters of the rolling bearings. 4 rolling bodies are conditionally given
f 1 - the rotation frequency of the rotor (of the inside ring of the bearing);
f 2 - the frequency of the rolling of the bearing bodies along the running slots of the outside rings
(Formula 2).
f
1 d4
f3
* Z f1(1
*cos
)* ;
(2)
2 d
2
Z
where:
3
f is the frequency of the separator rotation;
3
d - the diameter of the rolling bodies;
d
4
3
the diameter of the separator (diameter of the circle going through the centres of the
rotation bodies), and
d
d
d
2
1 2
3
;
d1
- the diameter of the running slot of the outside ring;
d
2
the diameter of the running slot of the inside ring;
α – the angle of the rolling bodies contact with the running slots;
Z- the number of rolling bodies.
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