Abstract:

Single-phase grounding fault is the most common fault causing insulation damage to generator stator windings. The grounding transformer high-resistance grounding mode widely used in China cannot address the problem of excessive grounding fault current induced by the increase in generator-to-ground capacitive current, while the combined grounding mode has the limitation of poor parameter adaptability in its application to large hydropower stations with different unit models. This paper proposes a flexible combined grounding mode, and takes the generators of five models in a hydropower station as the research object to optimize the design of their grounding devices, which verifies the feasibility of the flexible combined grounding device. This grounding mode can not only effectively limit key indicators such as single-phase grounding fault current, but also make up the deficiency in the universal adaptabilityof grounding device parameters, significantly reduce the costs and pressures of equipment installation and spare parts purchase and storage, and is of great significance to ensuring the operational safety of generators in large hydropower stations.

Key words: generator neutral point grounding, combined grounding mode, stator single-phase grounding fault, grounding device parameter design, restrike arc transient overvoltage