Research On Switching Overvoltage Of UHU AC Double Circuit Transmission Lines On The Same Tower

Ultra high voltage (UHV) transmission lines have higher voltage class and switching overvoltage level, more stringent request for allowable value of overvoltage level. Compared with single circuit, the electromagnetic transient process of double circuit transmission lines on the same tower is more complicated. The level of switching overvoltage determines the insulation level of UHV AC system. Therefore, it is necessary to research on the overvoltage level, influence factors and restrictive overvoltage measures of UHV AC double circuit transmission lines on the same tower.On the basis of Huainan-Shanghai UHV AC transmission project, this paper build the Ⅱ-type chain equivalent circuit model with distribute parameter characteristics. The principle is to divide the long lines into many segments, which equivalent to Ⅱ-type lumped parameter circuit model, and also consider line coupling capacitance and self-inductance. Then obtaining the differential equations of node voltage and branch current, and simplifying them into matrix form for numerical calculation. In this paper, using the phasor method to calculate the initial value of node voltage and branch current, and selecting the improved Euler method for solving differential equations by MATLAB.The switching overvoltage including ground fault, no-load closing, single-phase automatic reclosing, load shedding and fault clearance overvoltage. Their overvoltage value and waveform were obtained by program calculation. The no load closing overvoltage is most serious and the no fault load shedding overvoltage value is the lowest. The switching overvoltage level will be affected to different degrees by many factors, such as the length of lines, transport capacity, closing phase, operation condition and other factors. Studies have shown that high-voltage reactor, MOA, closing resistance and opening resistance have different effect on limiting overvoltage, and the combination of various measures to use more effective than a measure.Finally, use the software ATP-EMTP to model and simulation verification, compare the simulation results with the numerical results, it is proved that errors of the numerical results are in the accepted range. The results demonstrate that the Fl-type chain equivalent circuit model, formula derivation and the improved Euler numerical mothed are feasible and correct.