Broken Bars - Case History 1
Sea Water Injection Pump on an Offshore Oil Production Platform

Faulty Rotor AssemblyMultiple broken rotor bars
The rotor cage was in an extremely unhealthy state.

Secondary damage to the motor was possible from copper parts of the rotor hitting the stator winding end region at high velocity.

As this was a high voltage motor operating on an oil production platform safety implications were also considered.

Upon inspection it was found that 20 of the 46 rotor bars were broken.

This Case History proves that MCSA is a highly effective on-line diagnostic tool for the detection of rotor winding problems in comparison to vibration analysis.

EXPERT ANALYSIS & RECOMMENDATION

  • Figure b-2 shows the sidebands are only 26dB down on the supply frequency component.

  • This corresponds to an extremely unhealthy rotor cage in a SCIM, 2-pole motor with 46 rotor rotor bars.

  • The rotor was copper fabricated and there was a risk of secondary mechanical damage to the high voltage (6.6 kV) stator winding due to copper parts hitting, for example, the end winding region at high velocity.


Based on the Current Spectrum, design features of the motor and its operating environment it was recommended that this motor be...

REMOVED FROM SERVICE AS SOON AS PRACTICALLY POSSIBLE

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