A novel high-impedance neutral grounding method for medium- or large-size hydroelectric generators

Abstract

As the capacity of medium or large hydroelectric generators increases, conventional grounding methods face challenges in effectively limiting single-phase to earth fault current and neutral displacement voltage within acceptable range. Excessive fault current and neutral displacement voltage pose threats to the stability and safety of power generation and transmission systems. Inherent design deficiencies in conventional grounding methods lead to failures in meeting fault current and voltage requirements. To address this, this paper proposes a novel grounding method utilizing high impedance to restrict excessive fault current and neutral displacement voltage. The method minimizes both fault current and neutral displacement voltage by optimally selecting device parameters through minimal iterative trials. Additionally, a novel indicator is introduced to evaluate the effectiveness of grounding method by monitoring changes in neutral displacement voltage. The method is tested through theoretical calculation and field experiments, successfully implemented in large-size hydroelectric generator.