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Decatur Industrial Electric recently received an emergency field service request from a steel industry customer to troubleshoot the controls and inspect a 750HP, 900 RPM M-G set that would not start.
During inspection we found that the generator portion of the M-G set had serious issues with the interpole insulation. Between the core iron and the coils, the core insulation had completely disintegrated and turned to powder. Additionally, the line leads on the motor portion of the unit were oil soaked and swollen. It was determined that the unit needed to be removed and repaired at Decatur Industrial because it was impossible to properly test the unit in its current condition.
Upon arrival at our shop, we completely reconditioned the M-G set, which included removal of all the interpole coils, reinsulation, and a VPI treatment. We also rewired the DC internal connection and releaded the AC motor stator. Finally, we were able to properly troubleshoot the control problem and repair the faulty contacts.
Although we were unable to initially troubleshoot the controls due to the deteriorating insulation on the generator side of the unit, we saved the customer the cost of a complete M-G set rebuild which can cost upwards of $200,000. They paid less than half of that amount for our repair.