复杂接地系统冲击接地特性的数值计算及试验

为抑制变电站开关操作时产生的瞬态电磁场对站内二次设备的干扰,通常将二次电缆的屏蔽层双端接地。而雷击变电站接地网时,由于接地网的高频接地阻抗较大,在屏蔽层的两个接地点会产生很大的地电位差,这一电位差将通过二次电缆的转移阻抗耦合至二次设备,影响二次设备的正常工作。将矩量法与传输线理论相结合,将无穷远处视为零电位参考点,提出了分析复杂接地系统冲击接地特性的理论计算模型,该计算模型在频率不高或电缆长度较短的情况下,可简化为集中参数电路模型。为验证计算模型的正确性,还在试验接地网上进行了冲击接地试验,理论计算与测量结果比较吻合。该计算模型及方法可用于实际变电站接地网的冲击接地特性研究以及二次电缆电磁干扰的数值预测。

Numerical Calculation and Experimental Research of Impulse Grounding Performance of Complex Grounding System

To reduce the interference to secondary equipments caused by transient electromagnetic field due to switching operation in substations, generally the metal shields of secondary cables are connected to grounding grid at both ends. When lightning current injects into grounding grid, theoretically high ground potential difference between two grounding points of the cable shield will appear due to the high impedance of the grounding grid under high frequencies, and such a high potential difference will be coupled to secondary equipments through transfer impedance of secondary cables, thus the normal operation of secondary equipments will be affected. Combining the method of moment with transmission line theory and looking upon the position at infinite distance as the reference point of zero potential, a theoretical calculation model to analyze the impulse grounding performance of complex grounding system is proposed. To verify the correctness of the proposed calculation model, impulse grounding tests are performed by experimental grounding grid and the measured results can well coincide with the results from theoretical calculation. The proposed model and method can be applied in the research on impulse grounding performance tests of grounding grid in practical substations as well as the numerical forecasting of electromagnetic interference on the secondary cables.