Título: Very Accurate Time-Frequency Representation of Induction Motors Harmonics for Fault Diagnosis Under Load Variations
Autor: Bonet-Jara, Jorge; Fernández-Cavero, Vanessa; Vedreño Santos, Francisco Jose; Morinigo-Sotelo, Daniel; Pons Llinares, Joan
Resumen: [EN] Induction motors work under steady-state in many
applications. Nevertheless, in some cases they experience periodic
load fluctuations, which generate constant frequency harmonics
close to variable frequency bar breakage harmonics. In these cases,
time-frequency (t-f) transforms are better suited than steady-state
analysis since the fault harmonic frequencies change in time. Even
if the healthy and faulty frequencies do not overlap in the spectrum, if the speed is unknown, it is difficult to distinguish the
constant frequency healthy harmonic from the variable frequency
bar breakage harmonic. On the other hand, transient techniques
present in technical literature are not precise enough to deal with
both the changing frequency of the bar breakage harmonic and
a close constant frequency (as the one generated by most of the
periodic load fluctuations). To achieve reliable results under these
challenging situations, a very precise time-frequency transform
must be used, enabling to simultaneously draw the constant and
variable frequencies, even if they are very close in the t-f plane. The
Dragon-Transform is here proposed to address the problem. It is
shown through simulation and experimental results, how it enables
to very accurately plot up to five faulty harmonics evolutions,
distinguishing at the same time the constant frequency of the load
oscillation, traced as a very thin horizontal line. Precision is so high
that even the oscillations caused by ripple effect can be observed
for the first time in technical literature, enhancing the reliability of
the diagnosis performed, and opening the path for a true solution
of the problem.
