Research On Relay Protection For Series Compensation Transmission Line

Due to the increasing demand for electricity,the transmission capacity is increasing.The series capacitor compensation technology is widely used in high-voltage long-distance transmission lines because of its advantages of reducing electrical distance,increasing the transmission capacity of transmission lines,and improving the stability of power systems.in.However,the introduction of series capacitors changes the structural parameters of the power grid,destroys linear distribution of the impedance of the transmission line,and has a great influence on the electrical characteristics after the fault,resulting in problems such as voltage reversal,current reversal,and occurrence of low-frequency transient components.This brings the relay protection technology of the transmission line with series capacitor compensation great challenges.In this paper,the structure and working principle of the series compensation device are briefly introduced,including fixed series compensation(FSC)and thyristor controlled series compensation(TCSC).On the basis of understanding the series compensation structure,according to the actual series compensation transmission engineering parameters,relying on the PSCAD/EMTDC simulation software,a system simulation model including the series compensation device and the transmission line was built,and the theoretical derivation and simulation verification were used to illustrate the changes to the electrical characteristics of the transmission line with series capacitor compensation after failure.Then the article introduces the existing protection function of the series capacitor compensation circuit,and analyzes the impact of the series compensation.In addition,it points out the defects of the current two-terminal protection in the application of big supplemental transmission lines,such as insufficient sensitivity and lack of directionality.Aiming at the shortcomings of the two-terminal protection of the series-compensated transmission line,this paper proposes a series-compensated line protection based on the difference of double-end harmonic distortion rate and a new method of series-compensated line protection based on double-end harmonic amplitude fluctuation.The new method calculates the current measured at both ends of the line,and directly uses the difference characteristic of the current harmonic calculation amplitude to judge the fault position.It does not need to consider the voltage and current phase,realizes the full line protection of the series-compensated transmission line,and improves sensitivity and reliability of series-compensated line protection.The digital simulation results of PSCAD/EMTDC verify the correctness and effectiveness of the above protection algorithm.Finally,the paper concludes with a summary of the work done in the paper,and points out some problems in the series-compensation line protection method proposed in this paper and the next research direction.