Research On The Optimization And Layout Of Lines In The UHVDC Transmission Corridor

With the continuous development of electric power industry and the rapid increase of electricity consumption, a group of UHVDC transmission projects have been build and planned. It will inevitably lead to a shortage of the transmission line corridor resource. Transmission line corridor is designed for stable operation in order to ensure the safety of transmission and reduce the electromagnetic impact to the human body. A single transmission corridor includes two parameters, which are wire minimum height and corridor safety width. For multiple lines corridor, it also includes a proximity distance of the lines. In order to save the corridor resource and improve the power transmission capability of unit corridor, it can be used to optimize the DC line tower or plan the AC lines into UHVDC transmission corridor. But compared with the un-optimized corridor, the parameters in the transmission corridor will change and also have impact on electromagnetic environment. The electric field on the ground is one of the important indexes to control the corridor parameters and measure the personnel safety. Therefore, it is necessary to study the reasonable optimization and layout of the transmission lines in the resource-scarce regions, which can provide a reference for engineering practice and construction planning.Firstly, based on the assumption of Deutsch, the simplified algorithm of electric field distribution on the ground of UHVDC transmission line was derived and calculated. And the algorithm was validated with using the actual measurement parameters in the literature. At the same time, the impact of sub-wire radius, the number of sub-conductors, distance between the line and the height on the electric field of±800kV DC transmission line were analyzed. Through the research, it is recommended that a few split can be taken when the radius of conductor is large and a large split can be taken when the radius of conductor is small. Reducing the inter-electrode distance appropriately not only can reduce the electric field on the ground effectively, but also can save the width of transmission corridor. The minimum height of transmission line must be different in the different area.Then based on the second chapter, the optimization arrangement of pole wires which is vertical arrangement was put forward. The electric field intensity on the ground of the optimization arrangement was studied and compared with the situation of bipolar horizontal DC transmission line. The impact of horizontal spacing, vertical spacing and height of the pole line on the electric field was analyzed. The minimum height of line and safety corridor width which are the most important parameters were calculated and compared. Through the research, the DC transmission line which uses the optimized arrangement can greatly reduce the safety width of line corridors and improve the utilization of it. However, the maximum ground electric field with using this mode is larger than the horizontal ordering.Finally, a method to calculate the ground electric field when the±800kV DC transmission line and AC transmission line are parallel constructed in the same corridor was put forward. The impact of AC tower structure and phase sequence arrangement on electric field was analyzed. The limit standards to control the mixed electric field on the ground were discussed. The suitable close distance between lines and safety corridor width of hybrid lines when different voltage AC lines and DC transmission lines in the same corridor were studied. And the proposal of optimize and layout the hybrid lines in the same corridor was given in the paper. If the impact of AC lines on the ions that produced by the DC corona was ignored, the distribution of electric field on the gound of hybrid lines through the cycle is oval-shaped, which is similar to the AC transmission line. The impact of different structure of AC lines on the maximum electric field on the ground is small, but it will have a greater influence on the width of the entire corridor. In order to meet the electric field limit, the close distance are at least50m and80m when500kV and1000kV AC transmission lines close to the UHVDC transmission line. When AC transmission lines of different voltage appear in the UHVDC corridor, the AC line with low voltage was proposed to put in the middle of corridor. And increasing the height of AC lines apprppriate can effectively control the width of corridor.