500kV自耦变压器中性点小电抗接地在广东电网的应用研究

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。

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

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.