直流偏磁和剩磁同时作用下保护用电流互感器的暂态特性研究

Research on the transient characteristics of the protective CTS with co-impacts of DC bias and remnant flux

电力系统中电磁式电流互感器的暂态特性关系系统的安全稳定运行,通过建立直流偏磁条件下电流互感器的等效电路模型,利用基本电磁关系方程导出了剩磁和偏磁对保护用CT起始饱和时间和暂态饱和系数影响的定量数值关系。分析表明,直流偏磁将加速保护用CT的饱和,且偏磁电流越大互感器饱和越快。同时,剩磁与偏磁共同作用使得暂态饱和系数增大,如不考虑其变化,选择的CT可能不能满足偏磁条件下系统对CT的要求。通过仿真验证了理论分析结果的正确性。该研究为保护用CT的选择、继电保护的整定提供了参考依据。

The transient characteristics of protective electromagnetic current transformers are pivotal factors to ensure the stability of power systems. Equivalent circuit models of electromagnetic type protective CTs are established with DC bias. Combined with electromagnetic equations, the co-impacts from both DC bias and remnant flux on the time-to-saturation and the transient factor of protective CTs are deduced with quantitatively numerical expressions being given. The analysis indicates that the DC bias current will accelerate saturation of the protective CTs up to several milliseconds, and the CTs will saturate more quickly while the DC current becomes larger. In the meanwhile, the transient factor will be enlarged by the co-impacts, which results in that the selected CT won＇t fulfill the system demands. Simulations are presented to verify the above analyzed results. The proposed research presents useful reference for proper selection of protective CTs as well as reliable setting of corresponding relay device in power systems.