土壤电阻率的负温特性及冻土对接地极冲击响应的影响

doi:10.19595/j.cnki.1000-6753.tces.222233

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摘要

西藏地区由于独特的气候与地理环境,冻土地区存在雷电与低温共存现象。低温下冻土作为含冰复杂体系,在雷击下冲击散流性能仍不明晰,因此该文就冻土电阻率的负温特性以及接地极的冲击特性开展研究。首先研究了不同含水量、含盐量的土壤其电阻率随温度的变化规律;然后在冲击电流作用下,以永冻土试品的表层土壤融化厚度和季节性冻土试品的表层土壤冻结厚度为变量,探究了其对相应冻土中垂直接地极暂态电位的影响规律;最后通过结合冻结条件下土壤冲击放电的形貌特征与地中电场强度和电流密度的分布特性,探讨了负温下接地极暂态电位变化的本质原因。试验研究表明：考虑盐分对土壤的影响,当其温度在一次冻结温度T_f与二次冻结温度T_s之间时,电阻率随温度下降缓慢上升,只有当温度降至二次冻结温度时,才存在突增现象;在永冻土中,当冻土温度高于Ts时,接地极仍具有较好的散流性能。由此可知降低T_s可以减小水分冻结对土壤电阻率的影响,为避免极寒地区接地极失效提供了新思路。

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关键词 ：接地, 冻土, 冲击电流, 极寒低温, 土壤电离

Abstract：

Due to the unique geographical location and climate environment in Tibet, the coexistence of frozen soil and lightning current exists in the low temperature area, and the green energy transmission channel is difficult to avoid the low temperature area. However, as a complex system of water, ice, air and soil particles containing ice at negative temperature, the variation of soil resistivity with temperature under different water and salt contents and the impulse characteristics of grounding devices in frozen soil under lightning current are still unclear.
Therefore, in view of the above problems, on the one hand, the change of resistivity with temperature of 16 soil samples with different water content and salt content was measured by the quadrupole method, and the reasons for the change of soil resistivity were analyzed by combining the soil conductivity mechanism and the calculation formula of unfrozen water content; on the other hand, based on the similarity principle of the scale experiment, taking the surface soil freezing thickness of the seasonal frozen soil sample and the surface soil melting thickness of the permafrost sample as variables, the influence law of the vertical grounding electrode transient potential in the corresponding frozen soil sample was explored. Furthermore, the X-ray imaging device was used to observe the discharge image of the impulse current in the frozen soil sample and the numerical simulation results of electric field intensity and current density in the frozen soil were combined to explain the experimental law.
The measurement results of soil resistivity at different temperatures show that when the temperature of saline soil is higher than the secondary freezing temperature (T_s), its resistivity increases slowly with the decrease of temperature; when the temperature is lower than T_s, the resistivity has a sudden rise. The results of impulse current dispersion experiment of grounding electrode in permafrost show that when the temperature of permafrost layer is higher than T_s, the permafrost still has good current dispersion performance; the melting thickness of surface soil increases, and the potential of grounding electrode decreases slowly; when the melting thickness exceeds its end, the potential decreases greatly; however, when the temperature of the frozen soil layer is lower than T_s, the frozen soil with great resistivity will force the current to disperse in the surface thawing soil, and the grounding electrode potential is very small. The impulse current dispersion test results of the grounding electrode in seasonal frozen soil show that the grounding electrode potential will rise slowly with the increase of the freezing thickness of the surface soil; when the freezing thickness exceeds its end, the potential rise becomes larger.
The following conclusions can be drawn from the analysis of the results: (1) When the temperature of saline frozen soil decreases to T_s, a large amount of non-conductive ice and water salt will be generated, and the water content will decrease sharply, resulting in a sudden increase in soil resistivity. (2) The discharge image observation results and numerical simulation results of impulse current in frozen soil show that the current dispersion performance of frozen soil is inferior to that of thawed soil, and the soil ionization degree around the grounding extreme is the most serious, while the soil ionization is beneficial to the end current dispersion, therefore, when the thickness of the surface soil is greater than the length of the vertical grounding electrode, the change range of the transient potential of the grounding electrode will be greater. It can be seen from the above that by reducing the T_s of the soil, the grounding performance of the grounding device can be avoided to fail under extremely cold conditions.

Key words： Grounding frozen soil impulse current extremely cold temperature soil ionization

收稿日期: 2022-11-29

PACS:

TM863

基金资助:

国家自然科学基金面上项目资助（51777020）

通讯作者: 袁涛男,1976年生,副教授,博士生导师,研究方向为电力系统过电压防护及防雷接地技术、电磁兼容技术。E-mail：yuantao_cq@cqu.edu.cn

作者简介: 任健行男,1998年生,硕士研究生,研究方向为输电线路防雷接地。E-mail：1109073216@qq.com

引用本文:

袁涛, 任健行, 司马文霞, 常飞童, 蔡永翔, 肖小兵. 土壤电阻率的负温特性及冻土对接地极冲击响应的影响[J]. 电工技术学报, 0, (): 222233-222233. Yuan Tao, Ren Jianxing, Sima Wenxia, Chang Feitong, Cai Yongxiang, Xiao Xiaobing. Negative Temperature Characteristics of Soil Resistivity and Influence of Frozen Soil on Impulse Response of Grounding Electrode. Transactions of China Electrotechnical Society, 0, (): 222233-222233.

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