Research On Steady State And Transient Overvoltage Characteristics And Control Technology Of Half-wavelength Transmission Lines

The imbalance of energy resources and load demand in China determines that China must seek a new breakthrough in the long distance and UHV transmission technology of 1000km-3000km in the future.Due to its remarkable technical and economic advantages,half wavelength AC transmission technology has a strong competitive power and application prospect in the point to point distance and UHV transmission mode.However,the overvoltage problem is a major obstacle to the application of half wavelength transmission technology.On the basis of the existing research,this paper carries out innovative research on the overvoltage problem of the half wavelength AC transmission line:From the viewpoint of reactive power theory,the formation of overvoltage in the vicinity of the neutral point of the half wavelength transmission line is revealed.By introducing the equivalent impedance and power factor of the system,the formulas for calculating the amplitude and the position of the steady-state overvoltage are derived.A simulation model for the construction of UHV half wavelength AC transmission system is built with ATP-EMTP.According to the typical line fault and load rejection,the influence mechanism of transmission power on the overvoltage level is revealed.The influence of the equivalent power supply impedance and the actual length of the system on the half wavelength steady state characteristics of the transmission line is considered,Considering the influence of the equivalent power supply impedance and the actual length of the system on the steady state characteristics of the half wavelength transmission line,on the one hand,there may still be some overvoltage at the end of the line which shouldn't have existed.On the other hand,due to the influence of equivalent power supply impedance,the electrical distance of half wavelength AC transmission line increases,and the steady state characteristics and reactive power balance are destroyed.This paper puts forward the solutions to these two problems,adopting shunt reactor and reactive power compensation at the end of the line,respectively,to eliminate the no-load overvoltage at the end of the line and to relieve the steady-state overvoltage around the midpoint of the line.On the basis of the typical UHV metal oxide arresters(MOAs),overvoltage suppression effect of installing MOAs and circuit breaker with gate resistances are compared when single-phase reclosing and single-phase grounding fault happened,respectively.With the example of the overvoltage induced by single-phase grounding fault,over voltage suppression effect of lightning arrester installation and circuit breaker and gate resistance.The influence of the installation numbers and installation position of MOAs on the overvoltage suppression effect is simulated and analyzed for engineering reference.This paper focuses on the research aiming at exploring the key problems of voltage and power transmission characteristics,the steady state overvoltage along the midpoint of the line,power frequency overvoltage and overvoltage caused by fault simulation and suppression technology,reactive power and voltage control and so on,in order to build the foundation of theory and technology for the future development of half wavelength transmission.