500kV及220kV自耦变压器对电网单相短路电流的影响

Impact of using 500 kV and 220 kV autotransformers to the single-phase short circuit current

江苏部分500kV枢纽变电站220kV母线单相短路电流大于三相短路电流较多,且已经逼近了断路器的额定开断能力。主要是由于大量采用自耦变压器引起的,考虑更换自耦变为非自耦变以降低单相短路电流,实质是减少零序网接地支路。通过序网图原理分析发现更换500kV自耦变为非自耦变比更换220kV站内的自耦变为非自耦变对单相短路电流的抑制作用大,算例也证明了理论分析的正确性。但是更换500kV自耦变在技术和经济上可行性都不强,所以抑制单相短路电流的最有效措施是500kV自耦变中性点加装小电抗。

The single phase short circuit current is bigger than the three-phase short circuit current of 220 kV buses in some key 500kV stations of Jiangsu grid, and the single phase short circuit current exceeds the rated breaking ability of breakers. It is due to mass use of autotransformers, so the measure of using non-autotransformers instead of autotransformer to decrease the single-phase short-circuit current is considered. The essential of the measure is to reduce the earthing branches. It is found that the effect of replacing the 500kV autotransformers into non-transformers is better than that of replacing the 220kV autotransformers. As replacing 500kV autotransformers is not feasible, adding small reactance is still the most effective way to decrease the single-phase short circuit current.