In December 2009 , synchronous abnormal variations in geoelectric field observation and Z-com-ponent difference of geomagnetic field in central China were observed. After a careful investigation, it was confirmed that this phenomenon was caused by the trial operation of Baoji-Deyang ±500kV DC transmission project. HVDC is an important means to solve power transmission of long distance, but it can cause new interference in seismic geoelectric and geomagnetic field observations. In this paper,we analyzed the geomagnetic observation data from the stations nearby this HVDC project and calculated the impact of HVDC on geomagnetic observation under ideal conditions based on Amp theorem and Biot-Savart law. According to the calculations, the theoretical values are basically identical with the observed values, so the results are explanatory to the mechanism of the impact of HVDC on geomagnetic field observation. However,we did not take into account in the calculation the influencing factors, such as the difference between different geomagnetic observation systems and underground electrical structure,etc. So,the calculation method remains to be improved.%2009年12月,甘肃天水、陕西乾陵等地磁台Z分量观测差值出现台阶式异常变化,同期陕西关中地区宝鸡、乾陵、周至等台站地电场观测也出现同步异常变化.经调查落实,确认此变化是由宝鸡—德阳±500kV直流输电工程试运行引起的.高压直流输电是近年来新出现的地磁观测中的一类干扰异常.根据对宝鸡—德阳高压直流输电线路邻近区域各地磁台站实际观测资料的分析,并结合安培定理和毕奥-萨伐尔定律计算了理想状态下高压直流输电对地磁观测的影响.结果表明,理论值与实际观测值基本相符,从而从机理上解释了高压直流输电对地磁观测影响的原因.由于计算时没有考虑不同地磁观测系统的差异和地下电性结构等因素的影响,因此计算方法有待进一步完善.
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