Research On Ground Current Dispersion Characteristics And Monitoring Device Of Dc Grounding Electrode In Extremely Cold Region

DC technology develops rapidly these years,the number and voltage levels of DC transmission systems are increasing rapidly.When the DC transmission system is constructed in single pole mode during the initial stage or in a fault state,a larger current will flow directly from the ground electrode to the ground.If the current dispersion characteristics of grounding electrode are not good,it will seriously affect the nearby power equipment and buried metal pipelines.Moreover,there are seasonal frozen soils in Inner Mongolia,Xinjiang and other places.The frozen soil and its formation and melting process will seriously affect the effect of ground electrode current dispersion.And the maximum allowable value of ground electrode ground current in different frozen soil periods is different.It is of great significance to study the current dispersion characteristics of grounding electrodes under seasonal frozen soil conditions and to develop a monitoring device for grounding current.In this paper,the current dispersion characteristics of the common ground electrodes are studied.Then the effect of seasonal dynamic frozen soil on the grounding electrode is studied with a ring-shaped grounding electrode.A DC grounding electrode monitoring device was developed for monitoring the grounding current and environmental parameters in different frozen soil periods.And field tests were carried out.The main work of this article is as follows:(1)The ground electrode current field calculation model is established,and the common horizon,cross,and ring grounding electrodes with different ring numbers are compared and analyzed.It is found that a double ring ground electrode with an internal and external ring ratio of 0.725 has the best effect.(2)Aiming at the influence of seasonal frozen soil on the grounding electrode,a seasonal dynamic frozen soil model was established.The influence of the frozen soil on the ground electrode current dispersion during the formation and melting process is analyzed.It is found that the effect of ground electrode dispersion is the worst under completely frozen soil state,and the effect of current dispersion is best under melting state of frozen soil.Finally,the influence of frozen soil on the grounding electrode in Zhalut converter station is analyzed.;(3)The current dispersion characteristics of grounding electrode are different in different periods of seasonal frozen soil,and a DC grounding electrode current monitoring device has been developed.This device can measure the grounding current and environmental parameters.It can effectively warn in the seasonal frozen soil environment,which can effectively reduce the indirect economic loss caused by the failure.At the same time,the measurement results of the grounding current combined with the ground electrode current field calculation model can calculate the real-time ground electrode current state such as the ESP,step voltage,and surface current distribution characteristics.We conducted tests and verifications at Ximeng converter station.