500kV自耦变压器中性点小电抗接地在广东电网的应用研究

Research of Installing Small Reactors on Neutral Points of 500 kV Autotransformers in Guangdong Power Grid

广东电网500kV主网中自耦变压器的大量应用,使得系统零序阻抗迅速减小,导致单相短路电流超过三相短路电流,甚至超过了断路器遮断电流。针对部分站点三相短路电流较小、单相短路电流超标的特殊情况,本文提出在广东电网相关站点采用500kV自耦变压器中性点小电抗接地的方式,以降低单相接地短路电流水平,从而避免使用分母的方式限制短路电流。以广东电网典型500kV站点为算例,分析和计算该方法对短路电流的限制效果,并进一步对中性点电抗器的小电抗取值、主变中性点的过电压保护和绝缘配合问题进行了探讨。

With the extensive application of autotransformer in 500 kV power grid in Guangdong, the zero sequence impedance is reduced greatly, which makes single-phase short-clreuit current greater than three-phase short-circuit current, even greater than the maximum rated through current of the breaker. In order to reduce single-phase short-circuit current and avoid implement of bus split , this paper proposes to install small reactors on neutral points of 500 kV autotransformers in Guangdong power grid, and then analyzes and calculates the effect on short-circuit current limitation of this method. In addition, the impedance value of the small reactors, the protection of the neutral and autotransformer entrance, and insulation coordination are particularly discussed.