Research On Flexible Measures To Depress Overvoltage In UHV Transmission Lines

With the rapid development of our country’s economy and society, the contradiction between energy demand and energy supply is more and more outstanding. Due to energy uneven distribution and load center power supply nervous, make UHV(Ultra High Voltage) transmission project will start large-scale construction and put into use in the "125" period, the voltage stability of UHV grid is worth to pay more attention.Take the first1000kV UHV AC transmission pilot project of Jin Dongnan—Nanyang—Jingmen as an example, the closing and power frequency over-voltage of no-load transmission line is investigated by PSCAD_EMTDC power-system simulation software.This paper first analyzes the composition, produce mechanism and their characteristics of the power line overvoltage, lists several extensive use of restrictive measures of the frequency overvoltage and operating over-voltage in engineering, and compares the implementation effect of various types of over-voltage restrictive measures.Secondly, put forward the flexible measures to limit power frequency overvoltage, a small percentage of controlled reactor cooperate to use with a large percentage constant reactor. Accord operation mode of the line to control reactor, and the result shows that the small proportion controlled reactor used together with constant reactor not only save the project cost effective, and balance reactive demand of the transmission line. It can achieve the stability and reduce the reactive power flow in a variety of situations.Finally, given the lack of conventional methods on limiting UHV switching over-voltage, an effective and flexible method of restricting switching over-voltage is put forward in this paper, which substitutes time-controlled non-linear resistor for traditional closing resistor and multi-stage closing resistors. In selection of nonlinear resistors, seven types of representative change path of time-controlled nonlinear resistors are selected to lucubrate, and then analyze and compare with single-stage and multi-stage closing resistors which is a hotspot of study. The results of simulation indicates that time-controlled non-linear resistance Rt=R0-(Kt)1/3is markedly superior to single-stage, multi-stage and other types time-controlled non-linear closing resistors in terms of the limitation effect on switching over-voltage, and it takes over the complicated work of controlling multi-stage breaker circuit of multi-stage closing resistors.