The Electromagnetic Influences Of Geoelectric Field Observation From UHVDC Power Systems

China locates in an earthquake-prone zone, and the seismic electromagneticmonitoring stations throughout the country assume the important task of forecasting andmonitoring seismic activities. With more and more construction and commissioning ofUHV transmission lines, it has been unable to avoid the electromagnetic interference toseismic observations that surrounding the lines. In this paper, the electromagneticinterference from HVDC systems to seismic geoelectric field observation station arestudied in-depth, the mechanism of interference from HVDC system to the geoelectricfield observation is analyzed, the potential distribution model of earth-fault current inthree-dimensional combined-layer soil is proposed and a solving method for the potentialdistribution model is derived. Based on previous results, the correction system ofinterference from HVDC systems to the geoelectric field observations is developed. Themain contents are as follows:(1) The working principles of geoelectric field observation instrument are analyzed,and the characteristics of interference from DC transmission system to geoelectric fieldobservation is studied, it is believed that the total field of DC transmission line, ions intothe ground and earth-fault currents of grounding electrode are impact factors of theinterference.(2) Based on the assumption method of Deutseh, the lateral attenuation of total fieldand ion flow are studied by the method of simulation calculation and field measurementverification, it is believed that ion inflow may have a weak affect in the geoelectric fieldobservation and cause the interference amplitude of observation is uncertain. But theexistence of the DC lines will not make interference to the geoelectric field observations atkilometers away.(3) The potential distribution model of earth-fault current in three-dimensionalcombined-layer soil model is established, the complex multilayer soil structure’s Greenfunction can be get with infinite order Taylor series. Based on equivalent complex imagemethod, the potential distribution formula of grounding electrode’s earth-fault current inthree-dimensional combined-layer soil model is derived. The results show that theearth-fault current from ground electrode of transmission lines is the decisive impactfactor of the interference.(4) During the live debugging of±800kV Jinping-Sunan UHVDC transmission line,China Electric Power Research Institute (Wuhan), Three Gorges University, Institute of Earthquake China Earthquake Administration organize and carry out the interferenceexperiments of total field of DC transmission line and earth-fault currents of groundingelectrode to geoelectric field observation by the way of unite-observation with converterstation, seismic stations and field distribution. Comparative analysis of simulation resultsand experimental data found that the maximum error of interference calculation model isless than15%, and the correction system of interference from HVDC systems to thegeoelectric field observations is developed.