Minimizing the Phenomenon of Vibration Sparking through Reinforcement to Correct Partial Discharge Inception Voltage: A Case Study

Offline and online testing revealed that the generator tightening mechanisms had loose parts and there was an increase in the level of online partial discharge. The discharge was concentrated around 0° and 180° or around 90° and 270°, and the vibration-sparking was assumed to be a disturbance in the stator winding of the generator. Several findings were obtained from field observations, including the presence of black grease at the core end, greasing at the binding on the circuit ring, and end winding. It was also found that the partial discharge inception voltage (PDIV) of the stator winding occurred at 1 kV, which was an unusual PD inception voltage for a 20 kV rated voltage of a turbogenerator. The purpose of this case study was to reduce the vibration-sparking symptoms on a 300 MW turbogenerator by reinforcing the stator end winding. The following methods were applied to reduce the vibration-sparking symptoms: identifying problems, reinforcing the end winding, measuring direct bump tests along with reinforcement, comparing PDIV before and after reinforcement, and comparing online partial discharge tests before and after reinforcement. The reinforcement on the end winding shifted the resonant frequency of the stator end winding away from the power frequency of 95110 Hz. It also reduced vibration in the slot bar to some degree, which decreased the online PD magnitude compared to previous levels. PD inception voltage of stator winding increased from 1 kV to 6 kV, which is normal for a 20 kV turbogenerator. Reinforcement of end winding has been proven as a method to reduce the vibration-sparking symptom, decrease online PD magnitude, and increase partial discharge inception voltage of stator winding.