Research On Several Technology In UHV Transmission

To promote the intensive development of western coal and hydro resources, meet the growing demand for electricity in the eastern and middle part, alleviate enormous pressure of environmental pollution and shortage of land, China's UHV AC and DC transmission projects have entered steady construction period. But UHV transmission is still facing a lot of technical problems.With the improvement of the system operating voltage, Very Fast Transient Overvoltage (VFTO) in GIS is more harmful to the GIS insulation and transformers. Therefore, the VFTO problem in UHV power grid must been taken seriously. In this paper, VFTO limit level of insulation and characteristics of VFTO amplitude and steepness were combined to analyze the hazard to GIS insulation, transformer main insulation and longitudinal insulation in 1000kV and 500kV GIS system. Targeted and cost-effective suppression measures for VFTO were proposed. The relationship of sequence of operations and generated VFTO was analyzed. The results show that VFTO will endanger UHV GIS insulation and transformer longitudinal insulation except transformer main insulation. Transformer onnected by short overhead lines with GIS to protect transformer longitudinal insulation is proposed particularly. And the installation of shunt resistor in disconnector or ferrite bead in mentioned to protect the GIS insulation. In 500kV GIS system VFTO in only harmful to the transformer longitudinal insulation, Using short overhead lines connecting transformer and GIS can eliminate threat of VFTO to the entire 500kV GIS system.UHVDC transmission lines is facing severe lightning stroke in mountain area, and the trip-out rate of shielding failure for common T tower was high, thus the lightning protection of UHVDC transmission line in mountainous area has become a key technology for UHVDC transmission project. So a new tower called Z tower was designed specially for improving lightning withstand performance of shielding failure. Study on the Lightning Protection Performance and electromagnetic environment of Z tower has important significance to reasonable circuit design, safe and reliable line operation and requirements of environmental protection. Compared with T tower, the lightning withstand performances of back striking, shielding failure for Z tower of Zhexidu-Zhexi UHVDC transmission lines as well as related influencing factors were calculated and analyzed with EGM (Electro-geometrical Model) and EMTP (Elector-Magnetic Transient Program), and the electromagnetic environment of Z tower was evaluated with CDEGS and fomulas. The results show that Z tower's lightning withstand performance of shielding failure is better than that of T tower, and its lightning withstand performance of back flashover is high, overall the. lightning withstand performance of Z tower is superior to that of T tower. Under the lowest nominal height of the tower, all the electromagnetic environment parameters of Z tower can satisfy the requirements in national environmental standards, and all better than those of T tower. Z tower is more suitable for the mountain area.