The stator ground protection faults occurred twice in a 600MW generator. After extraction of rotor, it was found that the connection part of the stator bar with lead wire had been blown, and two fixed bolts fitting the lead wire have completely loosened. For analysis of ground-fault reasons, the generator stator end vibration analysis system was installed for on-line vibration monitoring of both sides end winding. The test results shown that the vibration of stator end winding exceeded the standard, and the main frequency component was the rotational frequency. The over-speed test and modal analysis determine that the resonance frequency of stator end wire was close to 50Hz. By increasing the stator cooling water temperature and adding sandbags, the resonance frequency of stator end wire avoid the generator operating frequency, and the end vibration was reduced to a safe level.

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