Bars - Case History 1
Sea Water Injection Pump on an Offshore Oil Production Platform
In this case history the current spectrum of a motor when in a healthy state is compared to the spectrum after a stall and 'direct-on-line' starts.
3-phase, star connected, SCIM,
6600 V, 60 Hz, 3.6 MW/4825 h.p.,
376 Amp, 3580 r.p.m
Copper fabricated rotor,
Single Cage, 46 rotor Bars,
Nose Joint rotor design of Bars to End-Ring,
Low full-load slip (0.0055, or 0.55%)
within this image for in-depth analysis
Original Current Spectrum from healthy unit
within this image for in depth analysis
Current Spectrum - high number of broken bars
MCSA FFT Current Spectrum
Dynamic Range = 80 dB
Frequency Resolution = 15 milliHertz/line
twice slip frequency sidebands for a nameplate frequency of 60 Hz and
a full-load speed of 3580 r.p.m. was ±0.66 Hz.
are greater than 45 dB down on the supply current.
Sidebands are due to inherent rotor assymmetry caused by differences in Bar to End-Ring joints.
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