三相三柱变压器零序阻抗的场路耦合计算与分析

Calculation and Analysis of Zero-Sequence Impedance of Three-Phase and Three Limbs Transformer Based on Field Circuit Coupled Method

变压器的零序阻抗是电力系统进行短路电流计算和继电保护整定的重要参数。对于变压器零序阻抗的计算,磁路法无法考虑外壳的弱磁作用,而单独的有限元方法又存在激励加载的困难。本文以YN联结的三相三柱电力变压器为研究对象,基于场路耦合的方法建立了变压器零序阻抗的有限元模型和统一的场路耦合数学模型,在此基础上分别计算了二次开路、短路情况时的一、二次绕组电流以及一次的零序阻抗,并对零序磁场的分布特点进行了深入研究,零序阻抗的计算与试验结果一致,验证了本文方法的正确性;同时,计算结果还表明:变压器油箱对主零序磁通有弱磁效果,当二次开路时,油箱的弱磁效果明显,而二次短路时的零序阻抗几乎不受油箱弱磁的影响。

Transformer zero-sequence impedance is an important parameter for short-circuit current calculating and relay protection setting in power system. In the conventional methods for calculating transformer zero-impedance, magnetic circuit method can not take into account the tank＇s field weakening effect and finite element method has the difficulty loading excitation. Based on field circuit coupled method, the finite element model and a unified mathematical model of YN connected three-phase and three limbs transformer are established, and the zero-sequence magnetic field and impedance are analyzed and computed under several conditions. The calculated results are well matched with the measured values, so the method in this paper is demonstrated to be effective. At the same time, this research also shows that the transformer tank has field weakening effect on the main zero-sequence magnetic flux. When the secondary winding is open, the tank field weakening effect is more obviously compared with that of short circuit.