Research On Current Field Distribution Of Circular Ring Grounding Electrode In HVDC Transmission System

With the emergence of large-capacity,long-distance high-voltage,ultra-high-voltage and ultra-high-voltage power grids,the working current of the DC grounding system will become larger and larger,which will affect the safe operation of the electrodes,the safety of humans and animals,and underground metal pipeline facilities.The safe operation poses a threat.The DC system ground current damages the electrical facilities around the pole site and even affects the safe operation of the entire AC-DC hybrid power grid.Compared with the linear grounding electrode,the current distribution density and potential distribution of the toroidal grounding electrode are relatively uniform,and there is no serious concentration of local current.Therefore,the circular ring grounding of the HVDC transmission system is studied.Current field distribution has practical engineering value.The shape and embedding mode of the DC grounding electrode are determined.The calculation formula of the ground potential distribution in different soil structures when the circular grounding electrode is not unequal buried is proposed.The ground potential distribution and stride voltage level around the grounding pole are studied.The method of calculating the soil structure simplification when calculating the surface potential distribution is discussed.The research results show that the calculation formula of the grounding potential of the ring-grounding pole of the HVDC system can be obtained on the basis of the point current source.The soil structure is different,and the obtained double-circular ring-shaped ground mirror image is also different.The simplification of the soil structure can improve the complexity.The speed at which soil stratification is calculated.The equivalent circuit is used to simulate the electrical characteristics of the buried metal pipeline,and the Kirchhoff theorem is used to derive the voltage on the buried metal pipeline.The formula of the diffuse density along the different axial directions of the DC double-circular grounding electrode in the semi-infinite uniform medium and the double-circular grounding pole overflow current density formula are proposed.The influence of the current density of the DC ground current on the surface interference voltage of the buried metal pipeline is discussed.The results show that when different soil structures are stratified,the double-circular grounding electrode leaks current through the ring to the ground,and the leakage current will increase the potential of the metal pipe.The grounding pole ring overflow current density is concentrated in the ring,and the maximum value of the grounding pole ring overflow current density is the radius of the grounding pole ring,the grounding pole overflow current density change and the buried metal pipe The change in surface potential is closely related.The calculation method for calculating the current shunt of the DC system into the ground is studied.The CDEGS software was used to establish the AC-DC hybrid grid model for the unipolar operation of the HVDC transmission system.The relationship between the influence of the DC current into the substation and the soil structure was discussed.The results show that the DC current into the ground is related to the soil structure.