双频式定子接地保护的分析与改进

Analysis and improvement of the dual frequency stator ground fault protection

介绍了基波零序电压保护原理、三次谐波电压幅值比保护原理、三次谐波电压幅值比突变量保护原理以及三次谐波电压矢量比较保护原理等四种定子接地保护原理,并根据三台汽轮发电机的参数,对上述原理进行灵敏度分析。分析表明基波零序电压保护原理与三次谐波电压矢量比较保护原理相配合时灵敏度最高,但该保护方案在大型机组采用接地变接地时灵敏度仍显不足。针对高压侧三次谐波电压的干扰,为了同时提高保护方案的灵敏度与可靠性,提出了一种改进方案。该方案在降低制动系数的同时增加了自适应制动门坎判据,仿真结果表明该方案能够兼顾灵敏度与可靠性。所得结论为定子接地保护的研发改进提供了参考。

Four protection principles for the stator ground fault are introduced： the fundamental frequency zero-sequence voltage principle, the third harmonic voltage amplitude ratio principle, the fault component of third harmonic voltage amplitude ratio principle and the third harmonic voltage vector comparison principle. The sensitivity of the four principles is analyzed based on the parameters of three turbine generators. Analysis shows that the best combination on sensitivity is the fundamental frequency zero-sequence voltage principle and the third harmonic voltage vector comparison principle. However, their sensitivity may be still insufficient in the case of large generator connected with the grounding transformer. In order to improve the sensitivity and the reliability of the dual frequency stator ground fault protection while considering the disturbance of the high side third harmonic voltage, an improved design is introduced. In this design, the braking coefficient is reduced and the threshold criterion is adaptive, which guarantees both the sensitivity and reliability. The conclusion of this paper can provide reference for the research and development of the stator ground fault protection.