Research On The Calculation Of Electrical Imbalance And Transposition Method Of Ultra-high Voltage Transmission Line

With the rapid development of China’s economy,the electricity load continues to increase,and the power grid continues to extend and expand.With the gradual increase of the voltage level,the length of transmission lines has increased year by year,especially for high-voltage and UHV lines.At present,there is no relevant provision on the allowable value of the electrical imbalance of a single line,according to the "110k V-750 k V overhead transmission line design code"(GB50545-2010)stipulates: "the neutral point directly grounded power grid,the length of more than 100 km of transmission lines should be transpositioned." According to this provision,a single-loop transmission line model is constructed,and the electrical imbalance of 100 km horizontal transmission lines is calculated,and then the allowable value of the electrical imbalance of the transmission line is stipulated.Electrical Power imbalance is a key indicator to judge the performance level and power quality level of high-voltage transmission lines,and reasonable control of this index is of great significance for transmission lines and the entire power system.In the transmission line,due to the imbalance of the parameters of the three-phase overhead line,when the line is running normally,the impedance and admittance of each phase of the wire are not equal,which causes the negative sequence and zero sequence current,too large the negative sequence current will cause the overheating of the motor in the system,it is possible to cause the ground relay with high sensitivity to malfunction,in accordance with the national standard "Power Quality Three-Phase Voltage Allowable Unbalance"(GB/T 15543-1995)requirements,it is necessary to control the imbalance of the system voltage and current.The paper conducts research and analysis on the imbalance of line voltage and current,and provides certain theoretical data support for future engineering design and construction.In view of the characteristics of transmission lines,this paper studies the electrical imbalance and transposition mode of single loop,double circuit of the same tower,single and double hybrid line and π line,and gives reasonable suggestions on the transposition mode and transposition point for various forms of transmission lines.