Analyzing Characteristics Of Half-wavelength Transmission System With Tuning Network

At present,the distance between western energy center and the eastern load center may reach or exceed 3000 km in China.There are more and more plans for long-distance transmission in the world.The high-power,long-distance power transmission technology needs to be studied urgently.Half-wavelength AC transmission technology as an ultra-long-distance transmission mode,its research has important significance.Based on the model of long transmission line,the transmission characteristics of uniform and non-uniform transmission lines have been analyzed in detail.The mathematical expression of the position and extremes of the voltage and current amplitude along a uniform transmission is given at different power levels.A sufficient condition for half-wavelength transmission has been proposed for nonuniform transmission lines.In order to analyze the transient characteristics of the half-wavelength transmission system,a discrete dynamic equivalent numerical simulation model has been established by using the split theory,based on half wavelength lumped parameter model.The model has the characteristics of simple structure,good numerical simulation stability and high precision.With this model,the no-load reclosing,load rejection and single-phase reclosing operation of the half wave transmission system have been simulated.When the uniform transmission line is less than half wavelength,the type of tuning network and its parameter determination method have been studied in detail.The parameter determination method of T type,? type and capacitive tuning network is given,based on the transmission parameter matrix of the uniform transmission.In the steady state,increase the electrical length by using capacitive tuning network,reducing the equivalent characteristic impedance and the increasing the equivalent natural power.for the use of T-type or ?-type tuning network compensation line length,the equivalent characteristic impedance and the equivalent natural power is unchanged.The influence of the number of capacitive tuning network and the location of T-type or ?-type tuning network on the voltage ratio,the line loss and the voltage distribution along the line have been analyzed.For the nonuniform transmission line,the tuning network structure has been given,and the parameter determination method has been given based on the transmission parameter matrix of the transmission line.For the half wavelength transmission line with tuning network,the transient characteristics of the ?-type and capacitive tuning networks have been analyzed.The transient overvoltage of the system with capacitive tuning network is smaller than that with ?-type tuning network.The influence of the number of capacitive tuning network,the fault current at the head-end bus and the length of the line on the transient process have been analyzed.For the problem of ?-type and capacitive tuning network internal capacitor voltage is too high,a reduction method has been proposed.The simulation results show that the ?-type and capacitive tuning network neutral point by resistance grounding can be effectively suppressed the transient overvoltage of the capacitor.