Study on the effect of different internal corona protection on electrical properties of generator stator bar

Dielectric loss factor (tanδ), largest repeatedly occurring PD magnitude and breakdown voltage of large generator stator bars with different internal corona protection were studied in this paper. It was found the electric properties which, the increment of tanδ, breakdown voltage and partial discharge magnitude etc. of the bars with internal corona protection were excelled than the bars without the structure. The loss factor of the bars fully shielded was smaller than those with partial shield layer. The dielectric loss factors of the fully shield bars were similarly but the partial discharge magnitude and breakdown voltage are very different depending on different structure of internal corona protection. These parameters could effectively characterize the electrical properties of large generator stator bars. The study had important reference for designing internal corona protection structure of large generator stator bars

INTRODUCTION

Stator bar is one of the most important parts in large generator. Rational insulation structural design of it plays a crucial role to the properties of generator. However, the conductor cross-section of the bars is rectangular, and the mutation of the rectangular cross-section caused electric field density concentration at the four corners. It will greatly reduce the electric strength and long-term running life of the insulation of the bars. Therefore, it is very important to research the method to improve the electric field distribution of conductor. It can improve the electrical performance of large generator stator bar and guarantee the generator running efficiently and reliably. In this paper, we studied the bars with different internal corona protection structures, and researched the dielectric parameters and partial discharge of these bars. According to the testing results, we discussed the effect of different internal corona protection structure on electrical properties of stator bars. This research will provide a reference structure for designing internal corona protecting for the stator bar of large generator.