用于抑制直流偏磁的接地电阻优化配置研究

我国天(生桥)—广(州)、三(峡)—常(州)等直流工程单极大地回路运行时均出现了直流偏磁问题,只在电流超标的变压器中性点安装抑制装置不能从根本上解决该问题。文章以全网变压器中性点接地电流不超标为目标,在分析直流网络的基础上提出基于伴随网络的接地电阻优化配置方法。在每次迭代求解过程中,在考虑了接地支路的约束条件下修改灵敏度最高的接地支路接地电阻,直到所有接地支路的中性点电流小于其限值。最后用南方电网的数据对该方法进行了验证,结果表明中性点电流被限制在限值以内,从而避免了直流偏磁的发生。

Optimized Grounding Resistance Configuration against DC Magnetic Bias of Large Capacity Power Transformer

In some domestic HVDC projects, e.g. HVDC from Tianshengqiao power station to Guangzhou and that from Three Gorges power station to Changzhou, the DC magnetic bias of large capacity power transformers occurs under monopole operation mode with earth return. This phenomenon cannot be settled at the root by installing suppression device at transformer's neutral only. Taking the grounding currents of transformers' neutrals of whole power network, which should not excess the specified value, as objective and on the basis of analyzing DC network, an adjoint network based optimized configuration method of grounding resistance is proposed. In each iteration solution process the grounded branch's grounding resistance with the highest sensitivity is modified until the neutral currents of all grounded branches are less than their specified value, while the constraint condition of grounded branches are taken into account. The proposed method is verified by the data from Southern China Power Grid, the verification results show that all neutral currents are limited within the specified value, thus the DC magnetic bias of power transformer is avoided.