500kV自耦变压器中性点小电抗接地应用研究

Study on 500kV Auto-Transformer Neutral Reactance in Hunan Power grid

限制单相短路电流的相关措施主要有限制变压器中性点直接接地数目、限制或不采用自耦变压器、发变组升压变压器中性点装快速接地开关、Y/Y/△接线自耦变压器三角形绕组侧开口以及变压器中性点经小电阻或小电抗接地等方式。变压器中性点经小电抗接地不仅不受电网运行的限制,还可降低变压器中性点绝缘水平,便于变压器制造。同时还可避免大量更换断路器的繁杂工作以及资金的浪费,具有良好的社会经济效益,而小电抗参数的选择是其中的关键环节。本文通过理论推导得出中性点经小电抗接地后的等值零序电抗计算公式,在此基础上采用电力系统分析综合程序(PSASP)计算主变经不同阻抗值小电抗接地时单相短路电流,并绘制曲线直观显示短路电流抑制效果。

Single phase short circuit current can be limited by reducing number of neutral ground,avoiding auto-transformer,fast grounding switch on boosting transformer in generator-transformer unit,Y/Y/△ auto-transformer △ side open circuit,and transformer neutral point grounded by small reactance. Transformer neutral point grounded by small reactance can be done without affecting power flow in power grid and can also lower the transformer insulation requirement and building costs.Meanwhile,it can avoid breaker changing,which means heavy workload and money waste,and the key is to choose the right parameters for the small reactance. This paper comes up with the equivalent zero sequence reactance formula through theoretical derivation. Based on the formula,power system analysis software package（ PSASP） is used to calculate single phase short circuit current with different reactance parameters,and curves are used to directly show the reactance limiting effect.