| Along with the electricity load continuously growth in china, the requirements of the voltage level and transmission capacity in the whole network is constantly improved. At the same time, the area of heavy load and energy in china is serious uneven distribution. The long distance, high power and cross-regional electric transportation properties in china, make the transfer capability of the whole power network under great pressure.HVDC transmission system has many advantages:the cost of transmission line is low, without the system stability problems, limiting short-circuit current, regulating the speed is faster, operation performance is reliable, low frequency oscillations can be eliminated in DC interconnection. AC fault can’t be transferee! in DC transmission system, chain effect in HVDC system contained the possibility of blackouts in large area is lower, So dc transmission technology is very suitable for long distance, high power and cross-regional transmission.As there is strong direct current injecting into the earth for HVDC to operate on ground-between return status, the potential on the surface would change widely and produce unfavorable effects on the transmission lines earth electrode, and the key to solve the problem is to discover the rules for the current in the earth. When DC current flows through the earth, there will be potential difference among different positions of the ground. If the DC earth electrode site near the transmission corridor, the DC current will flow among the towers with different equipotential surfaces through the shielding wires, which would lead to the corrosion of the tower is earth electrode.This paper takes CST EM STUDIO into the calculation of the ground current field, then we build a typical soil model and an accurate multi-layer soil model using CST EM STUDIO,A comparison is made between typical and multi-layer soil models of the earthy characters and near site surface potential. In addition, make the electrical model of the DC earth electrode, transmission line, ground wire tower grounding body and corresponding soil model are built under CST program in this paper.The DC current flowing through each tower and its distribution character are fully and syste-matically researched. According to the earth electrode design as the operation total number of years and the calculation result of current value from tower into the ground, under ratio of anode operation, the corrosion quantity of each tower and the total corrosion quantity of the transmission are obtained. Some conclusion can be gotten from the calculation results:the erossion quantity will be more with the increase of the resistivity of the middle earth layer and decrease of the grounding resistance of the tower. |
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