EXPERT
ANALYSIS & RECOMMENDATION
Faulty
Rotor Assembly
Aluminium
die-cast rotor, no visible damage.
Analysis
of the Motor Current Spectra in Figures (b-3) and (b-4).
Figure b-3 shows Motor (A);
No ±2sf1
sidebands, a perfectly healthy rotor
Fig
b-4 shows Motor (B);
There are ±2sf1
sidebands due to a faulty rotor winding.
The sidebands
are 34.35 dB (average) down on the supply frequency component (f1 )
and this corresponds to an unhealthy rotor winding.
Corrective
action had to be taken but several factors need to be considered in the
decision making process.
Since this was a die cast aluminium rotor the chance of secondary damage
to the stator winding is considerably less than with a copper fabricated
rotor (see Industrial Case History - 1).
Consideration
has to be given to the effects of the forces and subsequent vibration
caused by the rotor winding problem.
The pulsating
vibration on the bearings, gearbox, and drive shaft system can result
in accelerated mechanical wear and damage.
The process
demand had to be considered
and in this case the average load demand could be provided by the healthy
unit.
The RECOMENDATION was that Motor "B"
could be used as a standby and on light load
and that Motor "A" should take the load.
A
new rotor should be immediately ordered and installed upon delivery.
Back to Case History
|