多层水平土壤对交流电网直流分布的影响

Influence of Horizontal Multi-layer Soil on DC Current Distribution in AC Power Grid

直流输电入地电流在交流系统内分布,对变压器和电网造成不良影响。为探讨多层水平土壤情况下直流分布的规律,建立了直流分布的完整计算模型,通过数值计算分析了直流极的简化处理方法案和4层水平土壤对直流分布的影响。计算结果表明:在变电站距离大于10倍直流极尺寸的情况下可以用点电流源代替具体的直流极;场参数的求解是本模型关键,直流模型的场参数实质就是互阻,大型交流电网直流分布不能忽略变电站间互阻的影响;变电站接地电阻和地电位分布均受到大地参数作用呈现一致变化,但受影响程度不同,两者对交流电网总体直流分布的作用相反,造成直流分布呈现非线性变化;大地参数变化至一定程度时不会明显直流分布改变。

DC distribution in AC grid is caused by earth-return current of HVDC transmission.Adverse effect of transformer and AC grid is led by DC distribution.We established a complete model to analyze the laws of DC distribution under horizontal multi-layer soil,and used numerical methods to simplify the calculation of earth surface potential induced by DC electrode and to evaluate the DC distribution under 4-layer horizontal soil.The results reveal that,if any substation is away from 10 times as the DC electrode＇s dimension,the point source can be used as the specific DC electrode to obtain earth surface potential.Field parameter is the key point of the model while mutual resistance is the essence of field parameter.As to a large-scale power grid,mutual resistance can not be neglected.Soil parameters have the accordant influence on grounding resistance and ESP.But the influential degree is different.As grounding resistance and ESP has the adverse effect,DC distribution is nonlinear with grounding resistance and ESP.When soil parameters change to some extent,DC distribution is saturated.