VMI VIBER X5 MKIII, Instrument Manual, Page: 86 / 121

86
As you can see in the example the upper
and lower sidebands present in the
bottom picture at 23hz from the motors
frequency are have an amplitude of
53.9dB. They are caused by shorten
turns in the stator which produce
magnetic variations in the rotating field
similar to the effect on the rotor when it
has broken bars.
As the breakdown of insulation increases
these sidebands will increase in
amplitude more and decrease the
amplitude of the motors running
frequency, reducing torque eventually to
a point where the motor will be unable
to run. By detecting this breakdown of
insulation early we are able to take
corrective measures at an opportune
time to repair or replace the motor.
Full Range view is used to detect frequency components that are a function of airgap eccentricity.
There are two types of simultaneously occurring eccentricity, Static and Dynamic. Static eccentricity
is where the radial position of the minimal airgap length is fixed. This is caused by manufacturing
and part tolerances. Dynamic eccentricity is caused by the rotation of the minimal airgap with the
rotor and can be caused by non concentric outer rotor diameters of thermal bowing of the shaft.
The airgap eccentricity specified by a manufacturer is the radial airgap eccentricity (static plus
dynamic) and is
normally given
as a
percentage (e%) of the
nominal radial
airgap length (g).