M&C's stator rewind yield best ever test results

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IBG - SA Instrumentation & Control Buyers' Guide

November 2019 News

Marthinusen & Coutts recently provided a solution to an irregularity that occurred in the stator of a large 36 MW compressor motor deployed at Sasol’s Secunda plant.

Initially, a Sasol maintenance team discovered during a routine inspection that the flux shield mountings on the stator were faulty, whereupon Sasol awarded M&C; a contract to identify the cause of the irregularity and offer a solution.

“We tested the stator winding, which we found to be fine, but confirmed that there was a defect in the flux shield and recommended that it be repaired, as there was a risk of it damaging the winding if left to continue operating in its existing condition,” said Rob Melaia, M&C’s engineering and technical executive. “To repair the flux shield meant also having to remove the winding and perform a rewind on the stator.”

Sasol accepted M&C’s recommendation and assigned it to perform the required repairs. “In addition to replacing the old bars with new ones, we did a very specific modification to repair the flux shield to prevent a recurrence of the defect in the future,” explained Melaia.

“On investigating the defect we found that the electrical current, instead of flowing only in the flux shield as it ought to have done to prevent the core from overheating, had started flowing in the mounting bolts, so causing wear by electrical arcing in the mounting holes and the mounting studs,” he added.

The solution M&C’s repair team provided was to fit copper braid straps from several points on the flux shield to the stator body to reroute the current in such a way as to prevent a repeat of the damage as witnessed. To confirm the effectiveness of the solution M&C; arranged to have the refurbished stator tested by local independent test authority H.V. Test Field Services.

The results of the final tests were found to be the best among many conducted on similar equipment over a period of several decades. “We have every reason to be proud of this outcome as it says volumes about M&C’s expertise in this field, both in terms of correctly diagnosing and repairing faults in a wide range of large rotating equipment, as well as providing the appropriate and most effective solutions for them,” concluded Melaia.

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M&C's stator rewind yield best ever test results

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