Analysis On Electromagnetic Characteristics And Optimized Layout Of Common Corridor Consisting Of EHV/UHV AC/DC Transmission Lines

Transmission lines in common AC/DC transmission corridor, is an effective way of increasing the active power of corridor unit, and solving the contradiction between transmission project construction and land shortage. In common corridor, transmission lines of differing voltages are built densely relatively in this limited space. It will cause the coupling relationship between the lines is more complex, and the interference level is much higher. What’s more, there is more serious effect on power transmission and transformation equipment and transmission line maintenance. Recent research on electromagnetic characteristics, such as grounding electric field, electromagnetic coupling and electrical unbalance degree of AC and DC lines in common corridor, is not sufficient, leaving the problem unsolved. Based on the rapid development of EHV/UHV AC/DC transmission lines, it is important to investigate the electromagnetic characteristics and optimized layout of common corridor consisting of EHV/UHV AC/DC transmission lines.In this paper, the grounding electric field, electromagnetic coupling and electrical unbalance degree of AC and DC lines in common corridor have been investigated, and arrangement scheme was proposed based on the grounding electric field analysis.For the grounding electric field of AC and DC line in common corridor, the superimposed effect between AC power frequency electric field and DC total electric field was elaborated. The calculation method of hybrid electric field over the ground was studied, and its distribution characteristics were analyzed. It is concluded that hybrid electric field is affected greatly by the line parameters of structure, height and phase sequence arrangement. After analyzing the relationship of the power frequency electric field’s spatial vector distribution and voltage phase in the conductors, the influence of the lines’phase sequence arrangement on the electric field was investigated. The optimal phase sequence arrangement, corresponding to a minimum peak of the electric field in the corridor area, has been found.The effects of soil layer structure and electrical parameters on the calculation accuracy of the impedance of conductor-earth circuits for overhead line system have been analyzed. Based on distribution parameter theory, the method to calculate the electromagnetic coupling components of high voltage (HV) transmission lines in common corridor was put forward. It is applicable to HV transmission lines, which are not entirely parallel erected, and their nearby line section of a certain length. The distribution regularities of transverse voltage, longitudinal electromotive force and fundamental frequency current on the DC line were analyzed, and it is concluded that changing the topological structure of transmission line will have great influence on the coupling components. The principle, for HVAC and HVDC lines erected partially in parallel in common corridor, was proposed.In common corridor, the generation unbalance current in AC transmission line and its influential factors were analyzed. The calculation model of electrical unbalance degree of AC transmission lines in common corridor has been built. Through the research, the relationships between the unbalance degree and line arrangement, corridor path, active power, and so on, have been made clear. It is concluded that the nearby section’s length should be set according to the electrical unbalance degree, the number of nearby sections should be limited, and the relative ratio of active power should be limited at a low level. The mechanism, that the electromagnetic coupling between the lines influences the unbalance degree, was revealed. And the improvement effect of coupling ground wire on the electrical unbalance degree of AC line was studied.Based on typical parameters of transmission lines of differing voltages, the calculation models of grounding electric field have been established. And then, in common corridor, the grounding electric field in the optimal phase sequence arrangement was calculated. According to the limits of current standard in China, the minimum approaching distance of AC and DC line in common corridor was obtained. The level of coupling interference between transmission lines was evaluated, upon which the optimized arrangement scheme was proposed.